Naval Education and Training Command
NAVEDTRA 12204 May 1990 0502-LP-2 13-11 00
Training Manual (TRAMAN)
Machinery Repairman 3 & 2
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DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
Nonfederal government personnel wanting a copy of this document must use the purchasing instructions on the inside cover.
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S/N0502-LP-213-1100
The terms training manual (TRAMAN) and nonresident training course (NRTC) are now the terms used to describe Navy nonresident training program materials. Specifically, a TRAMAN in- cludes a rate training manual (RTM), officer text (OT), single subject training manual (SSTM), or modular single or multiple subject training manual (MODULE); and an NRTC includes nonresident career course (NRCC), officer correspondence course (OCC), enlisted correspondence course (ECC), or combination thereof.
Although the words "he," "him," and "his" are used sparingly in this manual to enhance communication, they are not intended to be gender driven nor to affront or discriminate against anyone reading this text.
DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
this document must write to Superintendent of Documents, t Commanding Officer, Naval Publications and Forms Center, tention: Cash Sales, for price and availability.
MACHINERY REPAIRMAN 3 & 2
NAVEDTRA 12204
1990 Edition Prepared by MRCM Reynaldo R. Romero
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PREFACE
This Training Manual (TRAMAN) and Nonresident Training Course (NRTC) form a self-study package to teach the theoretical knowledge and mental skills needed by the Machinery Repairman Third Class and Machinery Repairman Second Class. To most effectively train Machinery Repairmen, this package may be combined with on-the-job training to provide the necessary elements of practical experience and observation of techniques demonstrated by more senior Machinery Repairmen.
Completion of the NRTC provides the usual way of satisfying the requirements for completing the TRAMAN. The set of assignments in the NRTC includes learning objectives and supporting questions designed to help the student learn the materials in the TRAMAN.
1990 Edition
Stock Ordering No. 0502-LP-213-1100
Published by
NAVAL EDUCATION AND TRAINING PROGRAM MANAGEMENT SUPPORT ACTIVITY
UNITED STATES
GOVERNMENT PRINTING OFFICE WASHINGTON, D.C.: 1990
THE UNITED STATES NAVY
GUARDIAN OF OUR COUNTRY
The United States Navy is responsible for maintaining control of the sea and is a ready force on watch at home and overseas, capable of strong action to preserve the peace or of instant offensive action to win in war.
It is upon the maintenance of this control that our country's glorious future depends; the United States Navy exists to make it so.
WE SERVE WITH HONOR
Tradition, valor, and victory are the Navy's heritage from the past. To these may be added dedication, discipline, and vigilance as the watchwords of the present and the future.
At home or on distant stations we serve with pride, confident in the respect of our country, our shipmates, and our families.
Our responsibilities sober us; our adversities strengthen us.
Service to God and Country is our special privilege. We serve with honor.
THE FUTURE OF THE NAVY
The Navy will always employ new weapons, new techniques, and greater power to protect and defend the United States on the sea, under the sea, and in the air.
Now and in the future, control of the sea gives the United States her greatest advantage for the maintenance of peace and for victory in war.
Mobility, surprise, dispersal, and offensive power are the keynotes of the new Navy. The roots of the Navy lie in a strong belief in the future, in continued dedication to our tasks, and in reflection on our heritage from the past.
Never have our opportunities and our responsibilities been greater.
CONTENTS
CHAPTER Page
1. Scope of the Machinery Repairman Rating 1-1
2. Toolrooms and Tools 2-1
3. Layout and Benchwork 3-1
4. Metals and Plastics 4-1
5. Power Saws and Drilling Machines 5-1
6. Offhand Grinding of Tools 6-1
7. Lathes and Attachments 7-1
8. Basic Engine Lathe Operations 8-1
9. Advanced Engine Lathe Operations 9-1
10. Turret Lathes and Turret Lathe Operations 10-1
1 1 . Milling Machines and Milling Operations 11-1
12. Shapers, Planers, and Engravers 12-1
13. Precision Grinding Machines 13-1
14. Metal Buildup 14-1
15. The Repair Department and Repair Work 5-1
APPENDIX
I. Tabular Information of Benefit to
Machinery Repairmen AI-1
II. Formulas for Spur Gearing AIM
III. Derivation Formulas for Diametral Pitch System AIII-1
IV. Glossary AIV-1
INDEX INDEX-1
111
CREDITS
The illustrations indicated below are included in this edition of Machinery Repairman 3 & 2, through the courtesy of the designated companies, publishers, and associations. Permission to use these illustrations is gratefully acknowledged. Permission to reproduce these illustrations and other materials in this publication should be obtained from the source.
Source
Atlas Press Company, Clausing Corporation
Brown & Sharpe Manufacturing Company
Cincinnati Milacron Marketing Co.
Cincinnati Inc. Devlieg-Sundstrand DoAlI Company
Kearney & Trecker Corporation Lars Machine, Inc.
Monarch Tool Company
Rockford Line
SIFCO Selective Plating
South Bend Lathe Works
Warner & Swasey Co.
Figures
11-3
11-8, 11-9, 11-13, 11-14, 11-16, 11-17, 13-20
11-1, 11-2, 11-4, 11-5, 11-12, 11-13, 11-15, 11-18, 11-19, 11-20, 11-21, 11-83, 13-10, 13-11, 13-12, 13-15, 13-23, 13-24, 13-25
12-1, 12-3 10-42, 10-43
5-3, 5-5, 5-6, 5-7, 5-8, 5-9, 5-10, 5-11, 5-12, 5-13, 5-14, 5-15, 5-16, 5-17, 5-18, 5-19, 5-20, 5-21, 5-22, 5-23, 5-24
11-11
12-19, 12-20, 12-21, 12-22, 12-23, 12-24, 12-25, 12-26, 12-27, 12-28, 12-29, 12-30, 12-31, 12-32, and table 12-2
7-1 12-13
14-11, 14-12, 14-13, 14-14, 14-15, 14-16, 14-17, 14-18, 14-19, tables 14-3, 14-4, 14-5, 14-6, 14-7, 14-8, 14-9, 14-10, 14-11, 14-12 and all inserts in Chapter 14
7-2, 7-5, 7-6, 7-8, 7-9, 7-10, 7-11, 7-12, 7-13, 7-14, 7-15, 7-16, 7-17, 7-27, 7-29, 7-32, 7-33, 7-34, 7-35, 7-36, 7-37, 7-39, 7-40, 8-2, 8-4, 8-6, 8-9, 8-10, 8-11, 8-16, 8-18, 8-19, 8-20, 8-21, 8-22, 8-23, 8-24, 8-25, 8-26, 8-27, 8-28, 8-29, 9-2, 9-3, 9-4, 9-5, 9-6, 9-7, 9-8, 9-10, 9-11, 9-13, 9-19, 9-20, 9-21, 9-23, 9-24, 9-25, 9-30
10-3, 10-4, 10-5, 10-6, 10-7, 10-8, 10-9, 10-10, 10-11, 10-12, 10-13, 10-14, 10-15, 10-16, 10-17, 10-18, 10-19, 10-21, 10-24, 10-25, 10-26, 10-30, 10-31, 10-34, 10-35, 10-36, 10-37, 10-38, 10-39, 10-40, 10-41, 13-3, 13-13
IV
CHAPTER 1
SCOPE OF THE MACHINERY REPAIRMAN RATING
The official description of the scope of the Machinery Repairman rating is to "perform organizational and intermediate maintenance on assigned equipment and in support of other ships, requiring the skillful use of lathes, milling machines, boring mills, grinders, power hack- saws, drill presses, and other machine tools; portable machinery; and handtools and measuring instruments found in a machine shop." That is a very general statement, not meant to define completely the types of skills and supporting knowledge that an MR is expected to have in the different paygrades. The Occupational Standards for Machinery Repairman contain the require- ments that are essential for all aspiring Machinery Repairmen to read and use as a guide in planning for advancement.
The job of restoring machinery to good work- ing order, ranging as it does from the fabrication of a simple pin or bushing to the complete rebuilding of an intricate gear system, requires skill of the highest order at each task level. Often, in the absence of dimensional drawings or other design information, a Machinery Repairman must depend upon ingenuity and know-how to successfully fabricate a repair part.
One of the important characteristics you will gain from becoming a well trained and skilled Machinery Repairman is versatility. As you gain knowledge and skill in the operation of the many different types of machines found in Navy machine shops, you will realize that even though a particular machine is used mostly for certain types of jobs, it may be capable of accepting many others. Your imagination will probably be your limiting factor and if you keep your eyes, ears, and mind open, you will discover that there are many things going on around you that can broaden your base of knowledge. You will find a certain pleasure and a source of pride in develop- ing new and more efficient ways to do something that has become so routine that everyone else simply accepts the procedure currently being used as the only one that will work.
The skill acquired by a Machinery Repairman in the Navy is easily translated into several skills found in the machine shops of private industry. In fact, you would be surprised at the depth and range of your knowledge and skill compared to your civilian counterpart, based on a somewhat equal length of experience. The machinist trade in private industry tends to break job descriptions into many different titles and skill levels. The beginning skill level and one in which you will surely become qualified is "Machine Tool Operator," a job often done by semiskilled workers. The primary requirement of the job is to observe the operation, disengage the machine in case of problems and possibly maintain manual control over certain functions. Workers who do these jobs usually have the ability to operate a limited number of different types of machines. Another job description found in private industry is "Layout Man." The requirement of this job is to layout work that is to be machined by some- one else. An understanding of the operation and capabilities of the different machines is required, as well as the ability to read blueprints. As you progress in your training in the Machinery Repairman rating you will become proficient in interpreting blueprints and in planning the required machining operations. You will find that laying out intricate parts is not so difficult with this knowledge. A third job description is "Set- up Man," a job which requires considerable knowledge and skill, all within what you can expect to gain as a Machinery Repairman. A set- up man is responsible for placing each machine accessory and cutting tool in the exact position required to permit accurate production of work by a machine tool operator. An "All Around Machinist" in private industry is the job for which the average Machinery Repairman would qualify as far as knowledge and skill are concerned. This person is able to operate all machines in the shop and manufacture parts from blueprints. Some Machinery Repairmen will advance their knowledge and skills throughout their Navy career
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to the point that they could move into a job as a "Tool and Die Maker" with little trouble. They also acquire a thorough knowledge of engineer- ing data related to design limitations, shop math and metallurgy. There are many other related fields in which an experienced Machinery Repair- man could perform — instrument maker, research and development machinist, toolroom operator, quality assurance inspector, and of course the supervisory jobs such as foreman or superintendent.
The obvious key to holding down a position of higher skill, responsibility, and pay is the same both in the Navy and in private industry. You must work hard, take advantage of the skills and knowledge of those around you, and take pride in what you do regardless of how unimportant it may seem to you. You have a great opportunity ahead of you as a Machinery Repairman in the Navy; a chance to make your future more secure than it might have been.
TYPICAL ASSIGNMENT AND DUTIES
As a Machinery Repairman you can be assigned to a tour of duty aboard almost any type of surface ship, from a small fleet tug, which has a small 10- or 12-inch lathe, a drill press and a grinder, to a large aircraft carrier that is almost as well equipped in the machine shop as a tender or repair ship. You will find that although a ship's workspace is relatively small the machine shop will have more equipment than you might imagine. A lathe, drill press and grinder can almost be assured, but in many cases a milling machine and a second lathe are also available. A tender or repair ship is similar to a factory in the types of equipment that are installed. You will find the capabilities of such a ship to be very extensive in all areas required to maintain the complex ships of today's Navy. A Machinery Repairman is not destined to spend an entire career on sea duty. There are many shore establishments where you may be assigned. The Navy has shore-based repair activities located at various places throughout the United States and overseas. Most of these have wide-ranging capabilities for performing the required maintenance. There are general billets or assignments ashore that will not necessarily be associated with the Machinery Repairman rating, but which add to an individual's overall experience in other ways.
It would be difficult to detail the duties that you may perform at each of your assignments. You will find that on small ships you may be the only Machinery Repairman aboard. This requires that you be self-motivated toward learning all you can to increase your ability as a Machinery Repair- man and that you seek advice from sources off of your ship when you have an opportunity. You will be surprised at how good you really are when you make an honest effort to do your best. Regardless of your assignment, you will have an opportunity to work with personnel from other ratings. This can be an experience in itself. There are many interesting skills to be found in the Navy. None of them are easy, but many will offer you some amount of knowledge that will increase your effectiveness as a Machinery Repairman.
TRAINING
Training is the method by which everyone becomes knowledgeable of and skilled in any activity, whether it's a job, a sport or something as routine as eating the proper foods. Training can take many forms and can be a conscientious or unconscientious effort on your part. However, you will make the most progress when you recognize the need to increase your level of knowledge, take the required action to obtain the training and fully apply all your efforts and resources to realize the maximum benefit from the training. In the following paragraphs, we will present a brief description of each type of train- ing available to a Machinery Repairman. Keep in mind that the information listed is peculiar to your rating and that the Navy has many other programs available which will allow you to increase your general education. You can obtain information concerning these programs from your career counselor or education officer.
FORMAL SCHOOLS
The Navy has available several schools which provide an excellent background in the Machinery Repairman rating. You may have an opportunity to attend one or more of them during your career in the Navy.
The fundamentals of machine shop practice are taught in Machinery Repairman "A" school. Classroom instruction provides the theory of basic operating procedures, safety precautions and certain project procedures, while time spent in the shop provides hands-on experience, supervised by
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a trained and skilled instructor. Some of the equipment that you can expect to work with in this course are lathes, milling machines, drill presses, band saws, cutoff saws, pedestal grinders and engraving machines. The length and specific content of the course may vary from time to time to accommodate the needs of the fleet. You will have no difficulty in performing the work in a Navy machine shop if you apply yourself in MR "A" school.
Advanced machine shop practice and the heat treatment of metals are taught in Navy schools also. These courses are usually attended by personnel in their second and subsequent enlistments at "C" school. Course content generally covers the information and associated equipment required for advancement to MR1 and MRC, although the schools are not required to establish eligibility for advancement.
You should consult with your leading petty officer or career counselor to obtain the most current information regarding school availability and your eligibility to request attendance.
TRAINING MANUALS AND NONRESIDENT TRAINING COURSES
Navy training manuals and nonresident train- ing courses are designed as a self-study method to provide instruction to personnel in a variety of subjects. You can choose your own pace in working the courses, and you are allowed to refer to the book when trying to decide on the best or correct answer. If you are to learn anything, you must work the course yourself and not take the answers from someone else. Some training manuals and nonresident training courses are mandatory for you to complete to meet advance- ment requirements. These courses are listed in the Manual for Advancement, BUPERINST 1430.16 (series), and in the current (revised annually) issue of the Bibliography for Advancement Study, NAVEDTRA 10052 (series), where they are indicated by asterisks (*). Remember that as you advance you are responsible for the information in the training manuals for the paygrades below yours, in addition to the courses for the next higher paygrade. A course offers an excellent opportunity to become familiar with a subject when you cannot be personally involved with the equipment. There are many small but important points that will be covered in a course that you otherwise may not learn.
ON-THE-JOB TRAINING
On-the-job training is probably the most valuable of all the training methods available to you. This is where you put the textbook theories and general procedures into specific job practice in personal contact with the problem at hand. All those unfamiliar terms that you read about in a course now begin to fit into a plan that makes sense to you. The one very important thing for you to remember is that when you are unsure about something, ask questions. An unusual job experience is of little value to you if you have to wing your way through it tooth and nail, guess- ing at each new step. The people that you work with and for had to learn what they know by asking questions, so they won't think you any less efficient or valuable when you ask. There will be opportunities to tackle jobs which are difficult and seldom done, jobs which offer a great deal of experience and knowledge. These are the jobs that you should be really aggressive in pursuing and eager to accept. Regardless of the profession or the employer, the person who gets ahead is usually the one who is highly motivated toward increasing personal capacity, thereby, becoming more valuable to his or her employer. The Navy is no different than any other employer in this sense.
OTHER TRAINING MANUALS
Some of the publications you will use are subject to revision from time to time— some at regular intervals, others as the need arises. When using any publication that is subject to revision, be sure that you have the latest edition. When using any publication that is kept current by means of changes, be sure you have a copy in which all official changes have been made. Studying canceled or obsolete information will not help you do your work or advance; it is likely to be a waste of time, and may even be seriously misleading.
The training manuals you must use in conjunc- tion with this one to attain your required professional qualifications are:
1. Mathematics, Vol 1, NAVEDTRA 10069 and Mathematics, Vol. 2, NAVEDTRA 10071. These two volumes provide a review of the mathematics you will need in shop work.
2. Blueprint Reading and Sketching, NAVEDTRA 10077, provides information on blueprint reading and layout work.
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3. Tools and Their Uses, NAVEDTRA 10085, provides specific and practical information in the use of almost any handtool you are likely to use.
It is important that you keep abreast of required training manuals. To ensure that the most current manual is available, you should check the Bibliography for Advancement Study, NAVEDTRA 10052 (series), and List of Train- ing Manuals and Correspondence Courses, NAVEDTRA 10061 (series). Both of these references are revised annually, so be sure you have the latest one.
In addition, there are three sources of technical information that are ordinarily available on board your ship: (1) NAVSHIPS' Technical Manual, which contains the official word on all shipboard machinery, (2) technical manuals provided by the manufacturers of machinery and equipment used by the Navy, and (3) machinist's handbooks. Most of these books should be readily available. However, if they are not, your leading petty officer or division officer can request them through proper channels.
SAFETY
As a Machinery Repairman, you will be exposed to many different health and safety hazards every day. A great many of these are common to all personnel who work and live aboard a Navy ship or station, and some are peculiar only to personnel who are involved with jobs within machinery spaces. Information concerning these can be found in both the Fireman and Basic Military Requirements training manuals as well as instructions prepared by your command. In this section we shall look at some of the more common safety hazards you will find in a machine shop and some of the precautions you can take to prevent an injury to either yourself or someone else. You will find that safety is stressed throughout this manual as well as the importance of an individual's responsibility to not only be familiar with and observe all safe working standards personally, but also to encourage others to do so. Safety is a subject where the "learn by doing" method does not provide the greatest advantage.
Your eyes are one of your most priceless possessions. When you think about this and try to imagine how you would get along without them, you will agree that the slight inconvenience caused by wearing safety glasses, goggles or a face
shield is a small price to pay for eye protection. Wear safety glasses or goggles any time you are around machinery in operation, including hand- tools, whether powered or nonpowered. Safety glasses that have side guards are the most effective for keeping out small metal chips or particles from grinding wheels. You should wear a face shield and safety glasses at all times whenever you are around any grinding operation.
Another item of protection is safety-toe shoes. Granted, the additional weight of the steel reinforced toe does not make them the most comfortable shoes you can wear, but they do offer outstanding foot protection and are much more comfortable than a cast. Look around your shop at the dents left in the deck from objects being dropped. Do you think your unprotected foot would fare any better?
Some of the objects you will be handling in the shop will have sharp or ragged edges on them that can cut easily. You should remove as many of these "burrs" as possible with a file. In spite of your filing efforts, heavy objects will still cut easily where there is a corner. A pair of leather or heavy cotton work gloves will protect your hands in these cases. You should NOT wear gloves when operating machinery. The chances of their being caught are too great.
Loose fitting clothing worn around moving machinery will test your strength if it is caught in the rotating equipment. You would be amazed at the strength a shirt has when being wound up on a machine. Rings, bracelets and other jewelry can snag on projections of a rotating part and take a finger or other part of your body off before you know you have a problem.
How many times have you seen someone bend over and pick up a heavy object by using his or her back? Chances are this same person will eventually injure himself or herself. The correct way to lift any heavy object is to get as close to the object as you can, spread your feet about a foot apart and squat down by bending your knees. Keep your back straight during the lift. When you grasp the object, lift by using the muscles in your legs and hold the object close to your body. Walk slowly to your destination and lower the part exactly as you lifted it. If you have to lift something higher than your waist, seek assistance. Of course, there is a limit to how much weight anyone can safely pick up and this should not be exceeded.
Good housekeeping practices may demand a little more of your time than you are willing to give on some occasions, but this is just as
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important to a safe shop as any other measure you can take. Small chips made during a machining operation can become very slippery when allowed to collect on a steel deck. Long, un- broken chips can trip or cut someone walking past them. Lubricating oil that has seeped from a machine or a cutting oil thrown out by the machine can be an extreme hazard on a steel deck. All liquid spillage should be cleaned up right away. If your job is causing a hazard to other personnel by throwing chips or coolant into a passageway, speak with your supervisor about isolating the immediate area by stretching tape across the area. Unused metal stock, small and large parts of equipment being worked on, toolboxes and countless other objects should not be left laying around the shop where traffic can be expected to go or where a machine operator may have to be positioned. Most well organized shops have a place for storing all movable objects and this is the place for them. It will save you time when daily cleanup or field day comes along, and it may prevent a serious injury.
To protect yourself from injury while operating ship machinery, there are several things you can do. The first thing is to make sure that you know how the machine operates, what each control lever does, the capability of the machine and especially where the stop button or clutch lever is in case an emergency stop is required. All guards that cover gears, drive belts, pulleys or deflect chips should be in place at all times. Use the correct tool for the job you are doing. This means more than using a scraper to remove paint instead of a 6-inch ruler. Every machine or hand- tool has a safe working limit that was determined by considering the stresses it is subjected to during its intended use. Excessive pressures could cause machine or tool failure followed by injury.
Whenever you are operating a machine, give it your total concentration. Save daydreaming for a more relaxed time. If you must talk with some- one, shut your machine off.
Electrical safety is not the private respon- sibility of the electricians. They can keep the equipment operating safely if they are notified when a problem exists. They cannot make everyone observe safety precautions when work- ing around electrically powered equipment. This is a responsibility that each individual must accept and carry out.
The electrical systems used onboard ships are not like those found in your home, so however efficient you may feel you are as a handyman, do not attempt to make any repairs or adjustments
on any faulty equipment on board ship. Notify the electric shop and let the job be done by the trained electricians.
There are some basic safety precautions you can observe while using electrical equipment:
• Use only authorized portable electric equipment which has been tested by the electric shop within the prescribed time period and which is properly tagged to indicate such a test.
• Report all jury-rigged portable electrical equipment to the electric shop.
• When a plastic-cased or double-insulated electrically powered tool is available, use it in preference to an older metal-cased tool.
• Ensure that all metal-cased electrically powered tools have a three-conductor cable, a three-prong grounded plug and that they are plugged into the proper type receptacle.
• Wear rubber gloves when setting up and using the metal-cased tools or when working under particularly hazardous conditions and in environments such as wet decks.
• Notify the electric shop when you feel even a slight tingle while operating electrical equipment.
• Follow the safety precautions exactly as prescribed by your maintenance requirement cards when you perform maintenance on your equipment.
Always remember that electricity strikes without warning and, unfortunately, we cannot always sit around and discuss what went wrong after an accident has happened. It is to your advantage to ask when you are not sure of something. NEVER take unnecessary chances by hurrying or being inattentive. ALWAYS THINK about what your are going to do before you do it.
PURPOSES, BENEFITS, AND LIMITATIONS OF THE PLANNED
MAINTENANCE SYSTEM
You will soon find, if you have not done so already, that the continued operation of machinery depends on systematic and dedicated maintenance. The following paragraphs contain
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a brief discussion on the purposes, benefits, and limitations of the Navy's formal maintenance system, the Planned Maintenance System. You will be involved in the Planned Maintenance System, to some degree, throughout your career in the Navy.
PURPOSES
The Planned Maintenance System (PMS) was established for several purposes:
1. To reduce complex maintenance to simplified procedures that are easily identified and managed at all levels.
2. To define the minimum planned mainte- nance required to schedule and control PMS performance.
3. To describe the methods and tools to be used.
4. To provide for the detection and prevention of impending casualties.
5. To forecast and plan manpower and- material requirements.
6. To plan and schedule maintenance tasks.
7. To estimate and evaluate material readi- ness.
8. To detect areas that require additional or improved personnel training and/or improved maintenance techniques or attention.
9. To provide increased readiness of the ship.
BENEFITS
PMS is a tool of command. By using PMS, the commanding officer can readily determine whether his ship is being properly maintained. Reliability is intensified. Preventive maintenance reduces the need for major corrective maintenance, increases economy, and saves the cost of repairs.
PMS assures better records, containing more data that can be useful to the shipboard maintenance manager. The flexibility of the system allows for programming of inevitable changes in employment schedules, thereby help- ing to better plan preventive maintenance.
Better leadership and management can be realized by reducing frustrating breakdowns and irregular hours of work. PMS offers a means of improving morale and thus enhances the effectiveness of both enlisted personnel and officers.
LIMITATIONS
The Planned Maintenance System is not self- starting; it will not automatically produce good results. Considerable professional guidance is required. Continuous direction at each echelon must be maintained, and one individual must be assigned both the authority and the responsibility at each level of the system's operation.
Training in the maintenance steps as well as in the system will be necessary. No system is a substitute for the actual technical ability required of the officers and enlisted personnel who direct and perform the upkeep of the equipment.
SOURCES OF INFORMATION
One of the most useful things you can learn about a subject is how to find out more about it. No single jmblication can give you all the information yougieed to perform the duties of your rating. You should learn where to look for accurate, authoritative, up-to-date information on all subjects related to the naval requirements for advancement and the occupational standards of your rating.
NAVSEA PUBLICATIONS
The publications issued by the Naval Sea Systems Command are of particular importance to engineering department personnel. Although you do not need to know everything in these publications, you should have a general idea of where to find the information they contain.
Naval Ships' Technical Manual
The Naval Ships' Technical Manual is the basic engineering doctrine publication of the Naval Sea Systems Command. The manual is kept up-to-date by means of quarterly changes.
NAVSEA Deckplate
The NAVSEA Deckplate is a bimonthly technical periodical published by the Naval Sea Systems Command for the information of personnel in the naval establishment on the design, construction, conversion, operation, maintenance, and repair of naval vessels and their equipment, and on other technical equipment and on programs under NAVSEA's control. This magazine is particularly useful because it presents
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information that supplements and clarifies information contained in the Naval Ships' Technical Manual. It is also of considerable interest because it presents information on new developments in naval engineering. The NAVSEA Deckplate was formerly known as the NAVSEA Journal.
MANUFACTURER'S TECHNICAL
MANUALS
The manufacturers' technical manuals fur- nished with most machinery units and many items of equipment are valuable sources of information on construction, operation, maintenance, and repair. The manufacturers' technical manuals that are furnished with most shipboard engineering equipment are given NAVSHIPS numbers.
DRAWINGS
Some of your work as a Machinery Repair- man requires an ability to read and work from mechanical drawings. You will find information on how to read and interpret drawings in Blueprint Reading and Sketching, NAVEDTRA 10077 (series).
In addition to knowing how to read drawings, you must know how to locate applicable draw- ings. For some purposes, the drawings included in the manufacturers' technical manuals for the machinery or equipment may give you the information you need. In many cases, however, you will need to consult the on-board drawings. The on-board drawings, which are sometimes referred to as ship's plans or ship's blueprints, are listed in an index called the ship drawing index (SDI).
The SDI lists all working drawings that have a NAVSHIPS drawing number, all manufacturers' drawings designated as certifica- tion data sheets, equipment drawing lists, and assembly drawings that list detail drawings. The on-board drawings are identified in the SDI by an asterisk (*).
Drawings are listed in numerical order in the SDI. On-board drawings are filed according to numerical sequence. A cross-reference list of S-group numbers and consolidated index numbers is given in Ship Work Breakdown Structure.
ENGINEERING HANDBOOKS
For certain types of information, you may need to consult various kinds of engineering handbooks — mechanical engineering handbooks, marine engineering handbooks, piping hand- books, machinery handbooks, and other hand- books that provide detailed, specialized technical data. Most engineering handbooks contain a great deal of technical information, much of it arranged in charts or tables. To make the best use of engineering handbooks, use the table of contents and the index to locate the information you need.
ADDENDUM
In addition to a comprehensive index that is printed in the back of this manual, you will find the following:
1. Appendix I contains 23 tables, such as decimal equivalents of fractions; division of the circumference of a circle; formulas for length, area, and volume; tapers, and so forth. You will find this information helpful in your everyday shop work.
2. Appendix II contains formulas for spur gearing.
3. Appendix III shows the derivation of formulas for the diametral pitch system.
4. Appendix IV is a glossary of terms peculiar to the Machinery Repairman rating.
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CHAPTER 2
\
TOOLROOMS AND TOOLS
Your proficiency as a Machinery Repairman is greatly influenced by your knowledge of tools and your skills in using them. The information you will need to become familiar with the correct use and care of the many powered and non- powered handtools, measuring instruments, and gauges is available from various sources to which you will have access.
This training manual will provide information which applies to the tools and instruments used primarily by a Machinery Repairman. You can find additional information on tools that are commonly used by the many different naval ratings in Tools and Their Uses, NAVEDTRA 10085.
TOOL ISSUE ROOM
One of your responsibilities as a Machinery Repairman is the operation of the tool crib or tool issuing room. You should ensure that the necessary tools are available and in good condition and that an adequate supply of consumable items (oil, wiping rags, bolts, nuts, and screws) is available.
Operating and maintaining a toolroom is simple if the correct procedures and methods are used to set up the system. Some of the basic considerations in operating a toolroom are (1) the issue and custody of tools; (2) replacement of broken, worn, or lost tools; and (3) proper storage and maintenance of tools.
ORGANIZATION OF THE TOOLROOM
Shipboard toolrooms are limited in size by the design characteristics of the ship. Therefore, the space set aside for this purpose must be used as efficiently as possible. Since the number of tools required aboard ship is extensive, tool- rooms usually tend to be overcrowded. Certain peculiarities in shipboard toolrooms also require consideration. For example: The motion of the
ship at sea requires that tools be made secure to prevent movement. The moisture content of the air requires that the tools be protected from corrosion.
Permanent bins, shelves, and drawers cannot easily be changed in the toolroom. However, existing storage spaces can be reorganized by dividing larger bins and relocating tools to provide better use of space.
Hammers, wrenches, and other tools that do not have cutting edges may normally be stored in bins. They also may be segregated by size or other designation. Tools with cutting edges require more space to prevent damage to the cutting edges. Usually these tools are stored on shelves lined with wood, on pegboards, or on hanging racks. Pegboards are especially adaptable for tools such as milling cutters. Some provision must be made to keep these tools from falling off of the boards when the ship is rolling. Precision tools (micrometers, dial indicators and so forth) should be stored in felt-lined wooden boxes in a cabinet to reduce the effects of vibration. This arrange- ment allows a quick daily inventory. It also prevents the instruments from being damaged by contact with other tools. Rotating bins can be used to store large supplies of small parts, such as nuts and bolts. Rotating bins provide rapid selection from a wide range of sizes. Figures 2-1, 2-2, and 2-3 show some of the common methods of tool storage.
Frequently used tools should be located near the issuing door so that they are readily available. Seldom used tools should be placed in out of the way areas such as on top of bins or in spaces that cannot be used efficiently because of size and shape. Heavy tools should be placed in spaces or areas where a minimum of lifting is required. Portable power tools should be stored in racks. Provisions should be made for storage of electrical extension cords and the cords of electric power tools.
All storage areas such as bins, drawers, and lockers should be clearly marked for ease in
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Figure 2-1. — Method of tool storage.
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Figure 2-2. — Method of tool storage.
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Figure 2-3.— Method of tool storage.
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You will be responsible for the condition of all the tools and equipment in the toolroom. You should inspect all tools as they are returned to determine if they need repairs or adjustment. Set aside a space for damaged tools to prevent issue of these tools until they have been repaired.
You should wipe clean all returned tools and give their metal surfaces a light coat of oil. Check all precision tools upon issue and return to determine if they are accurate. Keep all spaces clean and free of dust to prevent foreign matter from getting into the working parts of tools.
Plan to spend a portion of each day recondi- tioning damaged tools. This is important in keep- ing the tools available for issue and will prevent an accumulation of damaged tools.
CONTROL OF TOOLS
You will issue and receive tools and maintain custody of the tools. Be sure that a method of identifying a borrower with the tool is established, and that provisions are made for periodic inventory of available tools.
There are two common methods of tool issue control: the tool check system and the mimeographed form or tool chit system. Some toolrooms may use a combination of both of these systems. For example: Tool checks may be used for machine shop personnel, and mimeographed forms may be used for personnel outside the shop.
Tool checks are either metal or plastic disks stamped with numbers that identify the borrower. In this system the borrower presents a check for each tool, and the disk is placed on a peg near the space from which the tool was taken. The advantage of this system is that very little time is spent completing the process.
If the tools are loaned to all departments in the ship, mimeographed forms generally are used. The form has a space for listing the tools, the borrower's name, the division or department, and the date. This system has the advantage of allowing anyone in the ship's crew to borrow tools and of keeping the toolroom keeper informed as to who has the tools, and how long they have been out.
You must know the location of tools and equipment out on loan, how long tools have been out, and the amount of equipment and consumable supplies you have on hand. To know this, you will have to make periodic inventories.
help you decide whether more strict control of equipment is required and whether you need to procure more tools and equipment for use.
Some selected items, called controlled equipage, will require an increased level of management and control due to their high cost, vulnerability to pilferage, or their importance to the ship's mission. The number of tools and instruments in this category under the control of a Machinery Repairman is generally small. However, it is important that you be aware of controlled equipage items. You can get detailed information about the designation of controlled equipage from the supply department of your activity. When these tools are received from the supply department, your department head will be required to sign a custody card for each item, indicating a definite responsibility for manage- ment of the item. The department head will then require signed custody cards from personnel assigned to the division or shop where the item will be stored and used. As a toolroom keeper, you may be responsible for controlling the issue of these tools and ensuring their good condition. If these special tools are lost or broken beyond repair, replacement cannot be made until the correct survey procedures have been completed. Formal inventories of these items are conducted periodically as directed by your division officer or department head.
As a toolroom keeper, you may have additional duties as a supply representative for your department or division. You can find information on procurement of tools and supplies in Military Requirements for Petty Officer 3 & 2, NAVEDTRA 10056.
SAFETY IN THE TOOLROOM AND THE SHOP
The toolroom, because of its relatively small size and the large quantity of different tools which are stored in it, can become very dangerous if all items are not kept stored in their proper places. At sea the toolroom can be especially hazardous if the proper precautions are not followed for securing all drawers, bins, pegboards, and other storage facilities. Fire hazards are sometimes overlooked in the toolroom. When you consider the flammable liquids and wiping rags stored in or issued from the toolroom, there is a real danger present.
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Several of your jobs are directly connected to the good working order and safe use of tools in the shop. If you were to issue an improperly ground twist drill to someone who did not have the experience to recognize the defect, the chances of the person being injured by the drill "digging in" or throwing the workpiece out of the drill press would be very real. A wrench which has been sprung or worn oversize can become a real "knucklebuster" to any unsuspecting user. An outside micrometer out of calibration can cause trouble if someone is trying to press fit two parts together using a hydraulic press. An electric- powered handtool that was properly inspected and tagged last week but has had the plug crushed since then can kill the user. The list of potential disasters that you as an individual have some influence in preventing is endless. The important thing to remember is that you as a toolroom keeper contribute more to the mission of the Navy than first meets the eye.
SHOP MEASURING GAUGES
Practically all shop jobs require measuring or gauging. You will most likely measure or gauge flat or round stock; the outside diameters of rods, shafts, or bolts; slots, grooves, and other openings; thread pitch and angle; spaces between surfaces; or angles and circles.
For some of these operations, you will have a choice of which instrument to use, but in other instances you will need a specific instrument. For example, when precision is not important, a simple rule or tape will be suitable, but in other instances, when precision is of prime importance, you will need a micrometer to obtain measure- ment of desired accuracy.
The term "gauge," as used in this chapter identifies any device which can be used to determine the size or shape of an object. There is no significant difference between gauges and measuring instruments. They are both used to compare the size or shape of an object against a scale or fixed dimension. However, there is a distinction between measuring and gauging which is easily explained by an example. Suppose that you are turning work in a lathe and want to know the diameter of the work. Take a micrometer, or perhaps an outside caliper, adjust its opening to the exact diameter of the workpiece, and
time to measure it, set the caliper at a reading slightly greater than the final dimension desired; then, at intervals during turning operations, gauge, or "size," the workpiece with the locked instrument. After you have reduced the workpiece dimension to the dimension set on the instrument, you will, of course, need to measure the work while finishing it to the exact dimension desired.
ADJUSTABLE GAUGES
You can adjust adjustable gauges by moving the scale or by moving the gauging surface to the dimensions of the object being measured or gauged. For example, on the dial indicator, you can adjust the face to align the indicating hand with the zero point on the dial. On verniers, however, you move the measuring surface to the dimensions of the object being measured.
Dial Indicators
Dial indicators are used by Machinery Repair- man in setting up work in machines and in checking the alignment of machinery. Proficiency in the use of the dial indicator will require a lot of practice, and you should use the indicator as often as possible to aid you in doing more accurate work.
Dial indicator sets (fig. 2-4) usually have several components that permit a wide variation
CLAMP AND CLAMP HOLDING INDICATOR R°D '
HOLDING ROD
HOLE ATTACHMENT
TOOL POST- HOLDER
Figure 2-4.— Universal dial indicator.
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nexiDiiity or setup, tne clamp and noiamg roas permit setting the indicator to the work, the hole attachment indicates variation or run out of inside surfaces of holes, and the tool post holder
When you are preparing to use a dial indicator, there are several things that you should check. Dial indicators come in different degrees of accuracy. Some will give readings to one
Figure 2-5 — Applications of a dial indicator.
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(0.005) of an inch. Dial indicators also differ in the total range or amount that they will indicate. If a dial indicator has a total of one hundred thousandths of an (0.100) inch in graduations on its face and has a total range of two hundred thousandths (0.200) of an inch, the needle will only make two revolutions before it begins to exceed its limit and jams up. The degree of accuracy and range of a dial indicator is usually shown on its face. Before you use a dial indicator, carefully depress the contact point and release it slowly; rotate the movable dial face so the dial needle is on zero. Depress and release the contact point again and check to ensure that the dial pointer returns to zero; if it does not, have the dial indicator checked for accuracy.
A vernier caliper (fig. 2-6) can be used to measure both inside and outside dimensions. Position the appropriate sides of the jaws on the surface to be measured and read the caliper from the side marked inside or outside as required. There is a difference in the zero marks on the two sides that is equal to the thickness of the tips of the two jaws, so be sure to read the correct side. Vernier calipers are available in sizes ranging from 6 inches to 6 feet and are graduated in increments of thousandths (0.001) of an inch. The scales on vernier calipers made by different manufacturers may vary slightly in length or number of divisions; however, they are all read basically the same way. Simplified instructions for interpreting the readings are covered in Tools and Their Uses, NAVEDTRA 10085.
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Figure 2-6. — Vernier caliper.
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out work for machining operations or to check the dimensions on surfaces which have been machined. Attachments for the gauge include the offset scriber shown attached to the gauge in figure 2-7. The offset scriber lets you measure from the surface plate with readings taken directly from the scale without having to make any calculations. As you can see in figure 2-7, if you were using a straight scriber, you would have to calculate the actual height by taking into account the distance between the surface plate and the zero mark. Some models have a slot in the base for the scriber to move down to the surface and a scale that permits direct reading. Another attachment is a rod that permits depth readings. Small dial
as a vernier caliper.
Dial Vernier Caliper
A dial vernier caliper (fig. 2-8) looks much like a standard vernier caliper and is also graduated in one-thousandths (0.001) of an inch. The main difference is that instead of a double scale, as on the vernier caliper, the dial vernier has the inches marked only along the main body of the caliper and a dial with two hands to indicate hundredths (0.100) and thousandths (0.001) of an inch. The range of the dial vernier caliper is usually 6 inches.
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Figure 2-7. — Vernier height gauge.
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A, MEASURING THE INSIDE
B. MEASURING THE OUTSIDE
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Figure 2-8.— Dial vernier caliper.
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Figure 2-9.— Dial bore gauge.
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a cylindrical bore or for checking a bore for out- of-roundness or taper is the dial bore gauge. The dial bore gauge (fig. 2-9) does not give a direct measurement; it gives you the amount of deviation from a preset size or the amount of deviation from one part of the bore to another. A master ring gauge, outside micrometer, or vernier caliper can be used to preset the gauge. A dial bore gauge has two stationary spring- loaded points and an adjustable point to permit a variation in range. These three points are evenly spaced to allow accurate centering of the tool in the bore. A fourth point, the tip of the dial indicator, is located between the two stationary points. By simply rocking the tool in the bore, you can observe the amount of variation on the dial. Accuracy to one ten-thousandth (0.0001) of an inch is possible with some models of the dial bore gauge.
Internal Groove Gauge
The internal groove gauge is very useful for measuring the depth of an O-ring groove or other recesses inside a bore. This tool lets you measure a deeper recess and one located farther back in the bore than if you were to use an inside caliper. As with the dial bore gauge, this tool must be set with gauge blocks, a vernier caliper, or an out- side micrometer. The reading taken from the dial indicator on the groove gauge represents the dif- ference between the desired recess or groove depth and the measured depth.
Universal Vernier Bevel Protractor
The universal vernier bevel protractor (fig. 2-10) is the tool you will use to lay out or measure angles on work to very close tolerances. The vernier scale on the tool permits measuring an angle to within 1/12° (5 minutes) and can be used completely through 360°. Interpreting the reading on the protractor is similar to the method used on the vernier caliper.
Universal Bevel
The universal bevel (fig. 2-11), because of the offset in the blade, is very useful for bevel gear work and for checking angles on lathe workpieces which cannot be reached with an ordinary bevel. The universal bevel must be set and checked with
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Figure 2-10. — Universal vernier bevel protractor.
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Figure 2-11.— Universal bevel.
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Gear Tooth Vernier Cutter Clearance Gauge
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Adjustable Parallel
Figure 2-12._Gear tooth vernier.
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2-12
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Figure 2-13. — Cutter clearance gauge.
minimum iimus. i ms msirumem, constructed to about the same accuracy of dimensions as parallel blocks, is very useful in leveling and positioning setups in a milling machine or in a shaper vise. An outside micrometer is usually used to set the adjustable parallel for height.
Surface Gauge
A surface gauge (fig. 2-15 is useful in gauging or measuring operations. It is used primarily in layout and alignment work. The surface gauge is commonly used with a scriber to transfer dimensions and layout lines. In some cases a dial indicator is used with the surface gauge to check trueness or alignment.
FIXED GAUGES
Fixed gauges cannot be adjusted. They can generally be divided into two categories, graduated and nongraduated. The accuracy of your work, when you use fixed gauges, will depend on your ability to determine the difference between the work and the gauge. For example, a skilled machinist can take a dimension accurately to within 0.005 of an inch or less when
Figure 2-14. — Adjustable parallel.
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SURFACE PLATE
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Figure 2-15. — Setting a dimension on a surface gauge.
using a common rule. Practical experience in the use of these gauges will increase your ability to take accurate measurements.
Graduated Gauges
Graduated gauges are direct reading gauges in that they have scales inscribed on them enabling you to take a reading while using the gauge. The gauges in this group are rules, scales, thread gauges, and feeler gauges.
RULES.— The steel rule with holder set (fig. 2-16A) is convenient for measuring recesses. It has a long tubular handle with a split chuck for holding the ruled blade. The chuck can be adjusted by a knurled nut at the top of the holder, allowing the rule to be set at various angles. The set has rules ranging from 1/4 to 1 inch in length.
The angle rule (fig. 2-16B) is useful in measuring small work mounted between centers on a lathe. The long side of the rule (ungraduated) is placed even with one shoulder of the work. The graduated angle side of the rule can then be positioned easily over the work.
Another useful device is the keyset rule (fig. 2-16C). It has a straightedge and a 6-inch machinist 's-type rule arranged to form a right angle square. This rule and straightedge combina- tion, when applied to the surface of a cylindrical workpiece, makes an excellent guide for drawing or scribing layout lines parallel to the axis of the work. You will find this device very convenient when making keyseat layouts on shafts.
You must take care of your rules if you expect them to give accurate measurements. Do not allow them to become battered, covered with rust, or otherwise damaged so that the markings cannot be read easily. Do not use them for scrapers, for once rules lose their sharp edges and square corners their general usefulness is decreased.
SCALES. — A scale is similar in appearance to a rule, since its surface is graduated into regular spaces. The graduations on a scale, however, differ from those on a rule because they are either larger or smaller than the measurements indicated. For example, a half-size scale is graduated so that
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ANGLE RULE
RULE WITH HOLDER
CENTER LINE OF WORK
KEYSEAT CLAMPS
Figure 2-16. — Special rules for shop use.
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1 inch on the scale is equivalent to an actual measurement of 2 inches; a 12-inch long scale of this type is equivalent to 24 inches. A scale, therefore, gives proportional measurements instead of the actual measurements obtained with a rule. Like rules, scales are made of wood, plastic, or metal, and they generally range from 6 to 24 inches.
ACME THREAD TOOL GAUGE.— This
gauge (fig. 2-17) is used to both grind the tool used to machine Acme threads and to set the tool up in the lathe. The sides of the Acme thread have an included angle of 29° (14 1/2° to each side), and this is the angle made into the gauge. The width of the flat on the point of the tool varies according to the number of threads per inch. The gauge provides different slots for you to use as a guide when you grind the tool. Setting the tool up in the lathe is simple. First, ensure that the tool is centered on the work as far as height is
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Figure 2-17.— Acme thread gauges.
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Figure 2-18. — Center gauge.
Figure 2-19. — Feeler (thickness) gauge.
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concerned. Then, with the gauge edge laid parallel to the centerline of the work, adjust the side of your tool until it fits the angle on the gauge very closely.
CENTER GAUGE.— The center gauge (fig. 2-18) is used like the Acme thread gauge. Each notch and the point of the gauge has an included angle of 60°. The gauge is used primarily to check and to set the angle of the V-sharp and other 60 ° standard threading tools. The center gauge is also used to check the lathe centers. The edges are graduated into 1/4, 1/24, 1/32, and 1/64 inch for ease in determining the pitch of threads on screws.
FEELER GAUGE.— A feeler (thickness) gauge, like the one shown in figure 2-19, is used to determine distances between two closely mating surfaces. This gauge is made like a jackknife with blades of various thicknesses. When you use a combination of blades to get a desired gauge thickness, try to place the thinner blades between the heavier ones to protect the thinner blades and to prevent their kinking. Do not force blades into openings which are too small; the blades may bend and kink. A good way to get the "feel" of using a feeler gauge correctly is to practice with the gauge on openings of known dimensions.
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Figure 2-20. — Fillet or radius gauges.
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Figure 2-21. — Straightedge.
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Figure 2-22. — Machinist's square.
RADIUS GAUGE.— The radius gauge (fig. 2-20) is often underrated in its usefulness to the machinist. Whenever possible, the design of most parts includes a radius located at the shoulder formed when a change is made in the diameter. This gives the part an added margin of strength at
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Figure 2-23.— Sine bars.
that particular place. When a square shoulder is machined in a place where a radius should have been, the possibility that the part will fail by bend- ing or cracking is increased. The blades of most radius gauges have both concave (inside curve) and convex (outside curve) radii in the common sizes.
Nongraduated Gauges
Nongraduated gauges are used primarily as standards, or to determine the accuracy of form or shape.
STRAIGHTEDGES.— Straightedges look very much like rules, except that they are not graduated. They are used primarily for checking surfaces for straightness; however, they can also be used as guides for drawing or scribing straight lines. Two types of straightedges are shown in figure 2-21. Part A shows a straightedge made of steel which is hardened on the edges to prevent wear; it is the one you will probably use most often. The straightedge shown in Part B has a knife edge and is used for work requiring extreme accuracy.
balance points. When a box is not provided, place resting pads on a flat surface in a storage area where no damage to the straightedge will occur from other tools. Then, place the straightedge so the two balance points sit on the resting pads.
MACHINIST'S SQUARE.— The most com- mon type of machinist's square has a hardened steel blade securely attached to a beam. The steel blade is NOT graduated. (See fig. 2-22.) This instrument is very useful in checking right angles and in setting up work on shapers, milling machines, and drilling machines. The size of machinist's squares ranges from 1 1/2 to 36 inches in blade length. You should take the same care of machinist's squares, in storage and use, as you do with a micrometer.
SINE BAR.— A sine bar (fig. 2-23) is a precision tool used to establish angles which required extremely close accuracy. When used in conjunction with a surface plate and gauge blocks, angles are accurate to 1 minute (1/60°). The sine bar may be used to measure angles on work and to lay out an angle on work to be machined, or work may be mounted directly to the sine bar for machining. The cylindrical rolls and the parallel bar, which make up the sine bar, are all precision ground and accurately positioned to permit such close measurements. Be sure to repair any scratches, nicks, or other damage before you use the sine bar, and take care in using and storing the sine bar. Instructions on using the sine bar are included in chapter 3.
PARALLEL BLOCKS.— Parallel blocks (fig. 2-24) are hardened, ground steel bars that are used in laying out work or setting up work for machin- ing. The surfaces of the parallel block are all either
.
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Figure 2-24. — Parallel blocks.
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pairs and in standard fractional dimensions. Use care in storing and handling them to prevent damage. If it becomes necessary to regrind the parallel blocks, be sure to change the size stamped on the ends of the blocks.
GAUGE BLOCKS.— Gauge blocks are used as master gauges to set and check other gauges and instruments. Their accuracy is from eight millionths (0.000008) of an inch to two millionths (0.000002) of an inch, depending on the grade of the set. To visualize this minute amount, consider that the thickness of a human hair divided 1 ,500 times equals 0.000002 inch. This degree of accu- racy applies to the thickness of the gauge block, the parallelism of the sides, and the flatness of the surfaces. To attain this accuracy, a fine grade of hardenable alloy steel is ground and then lapped until the gauge blocks are so smooth and flat that when they are "wrung" or placed one atop the other in the proper manner, you cannot separate them by pulling straight out. A set of gauge blocks has enough different size blocks that you can estab- lish any measurement within the accuracy and range of the set. As you might expect, anything so accurate requires exceptional care to prevent damage and to ensure continued accuracy. A dust- free temperature-controlled atmosphere is pre- ferred. After use, wipe each block clean of all marks and fingerprints and coat it with a thin layer of white petrolatum to prevent rust.
MICROMETER STANDARDS.— Microm- eter standards are either disk- or tubular-shaped gauges that are used to check outside micrometers for accuracy. Standards are made in sizes so that any size micrometer can be checked. They should be used on a micrometer on a regular basis to ensure continued accuracy. Additional informa- tion for the use of the standards are given later in this chapter.
RING AND PLUG GAUGES.— A ring gauge (fig. 2-25) is a cylindrically-shaped disk that has a precisely ground bore. Ring gauges are used to check machined diameters by sliding the gauge over the surface. Straight, tapered, and threaded diameters can be checked by using the appropriate gauge. The ring gauge is also used to set other measuring instruments to the basic dimension required for their operation. Normally, ring gauges are available with a "GO" and a "NO GO" size that represents the tolerance allowed for the particular size or job.
A. PLAIN CYLINDRICAL PLUG GAUGE
GAUGE LINE TAPER PLUG GAUGE
c. PLAIN CYLINDRICAL RING GAUGE
•GAUGE LINE 0. TAPER RING GAUGE
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Figure 2-25. — Ring gauge and plug gauge.
A plug gauge (fig. 2-25) is used for the same types of jobs as a ring gauge except that it is a solid shaft-shaped bar that has a precisely ground diameter for checking inside diameters or bores.
THREAD MEASURING WIRES.— The
most accurate method of measuring the fit or pitch diameter of threads, without going into the expensive and sophisticated optical and comparator equipment, is thread measuring wires. The wires are accurately sized, depending on the number of threads per inch, so that when they are laid over the threads in a position that allows an outside micrometer to measure the distance between them, the pitch diameter of the threads can be determined. Sets are available that contain all the more common sizes. Detailed information on computing and using the wire method for measuring is covered in chapter 9.
MICROMETERS
Micrometers are probably the most often used precision measuring instruments in a machine shop. There are many different types, each designed to permit measurement of surfaces for various applications and configurations of workpieces. The degree of accuracy obtainable from a micrometer also varies, with the most common graduations being from one thousandth of an inch (0.001) to one ten-thousandth of an inch (0.0001). Information on the correct
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the more common types of micrometers is often called a micrometer caliper, or mike, is used provided in the following paragraphs. to measure the thickness or the outside diameter
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Figure 2-26. — Common types of micrometers. 2-19
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Figure 2-27. — Nomenclature of an outside micrometer calipcr.
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of parts. They are available in sizes ranging from 1 inch to about 96 inches in steps of 1 inch. The larger sizes normally come as a set with inter- changeable anvils which provide a range of several inches. The anvils have an adjusting nut and a locking nut to permit setting the micrometer with a micrometer standard. Regardless of the degree of accuracy designed into the micrometer, the skill applied by each individual is the primary factor in determining accuracy and reliability in measurements. Training and practice will result in a proficiency in using this tool that will benefit you greatly.
Inside Micrometer
An inside micrometer (fig. 2-26) is used to measure inside diameters or between parallel surfaces. They are available in sizes ranging from 0.200 inch to about 107 inches. The individual interchangeable extension rods that are assembled to the micrometer head vary in size by 1 inch. A small sleeve or bushing, which is 0.500 inch long, is used with these rods in most inside micrometer sets to provide the complete range of sizes. Using the inside micrometer is slightly more difficult than using the outside micrometer, primarily because there is more chance of your
not getting the same "feel" or measurement each time you check the same surface.
The correct way to measure an inside diameter is to hold the micrometer in place with one hand as you "feel" for the maximum possible setting of the micrometer by rocking the extension rod from left to right and in and out of the hole. Adjust the micrometer to a slightly larger measurement after each series of rocking movements until no rocking from left to right is possible and you feel a very slight drag on the in and out movement. There are no specific guidelines on the number of positions within a hole that should be measured. If you are check- ing for taper, you should take measurements as far apart as possible within the hole. If you are checking for roundness or concentricity of a hole, you should take several measurements at different angular positions in the same area of the hole. You may take the reading directly from the inside micrometer head, or you may use an out- side micrometer to measure the inside micrometer.
Depth Micrometer
A depth micrometer (fig. 2-26) is used to measure the depth of holes, slots, counterbores, recesses, and the distance from a surface to some
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the closed end of the thimble. The measurement is read in reverse and increases in amount (depth) as the thimble moves toward the base of the instrument. The extension rods come either round or flat (blade-like) to permit measuring a narrow, deep recess or groove.
Thread Micrometer
The thread micrometer (fig. 2-26) is used to measure the depth of threads that have an included angle of 60°. The measurement obtained represents the pitch diameter of the thread. They are available in sizes that measure pitch diameters up to 2 inches. Each micrometer has a given range of number of threads per inch that can be measured correctly. Additional information on using this micrometer can be found in chapter 9.
Miscellaneous Micrometers
The machine tool industry has been very responsive to the needs of the machinist by design- ing and manufacturing measuring instruments for practically every imaginable application. If you find that you are devising measuring techniques for a particularly odd application with the resulting measurements being of questionable value and that you do it on a routine basis, maybe a special micrometer will make your work easier and more reliable. Some of the special micrometers that you may have a need for are described below.
BALL MICROMETER.— This type microm- eter has a rounded anvil and a flat spindle. It can be used to check the wall thickness of cylinders, sleeves, rings, and other parts that have a hole bored in a piece of material. The rounded anvil is placed inside the hole and the spindle is bought into contact with the outside diameter. Ball attachments that fit over the anvil of regular out- side micrometers are also available. When using the attachments, you must compensate for the diameter of the ball as you read the micrometer.
BLADE MICROMETER.— A blade microm- eter has an anvil and a spindle that are thin and flat. The spindle does not rotate. This micrometer is especially useful in measuring the depth of narrow grooves such as an O-ring seat on an out- side diameter.
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increases as you turn the micrometer. It is used to measure the width of grooves or recesses on either the outside or the inside diameter. The width of an internal O-ring groove is an excellent example of a groove micrometer measurement.
CARE AND MAINTENANCE OF GAUGES
The proper care and maintenance of precision instruments is very important to a conscientious Machinery Repairman. To help you maintain your instruments in the most accurate and reliable condition possible, the Navy has established a calibration program that provides calibration technicians, the required standards and pro- cedures, and a schedule of how often an instrument must be calibrated to be reliable. When an instrument is calibrated, a sticker is affixed to it showing the date the calibration was done and the date the next calibration is due. Whenever possible, you should use the Navy calibration program to verify the accuracy of your instru- ments. Some repair jobs, due to their sensitive nature, demand the reliability provided by the program. Information concerning the procedures that you can use in the shop to check the accuracy of an instrument is contained in the upcoming paragraphs.
Micrometers
The micrometer is one of the most used, and often one of the most abused, precision measuring instruments in the shop. Careful observation of the do's and don'ts listed below will enable you to take proper care of the micrometer you use.
1. Always stop the work before taking a measurement. Do NOT measure moving parts because the micrometer may get caught in the rotating work and be severely damaged.
2. Always open a micrometer by holding the frame with one hand and turning the knurled sleeve with the other hand. Never open a micrometer by twirling the frame, because such practice will put unnecessary strain on the instru- ment and cause excessive wear of the threads.
3. Apply only moderate force to the knurled thimble when you take a measurement. Always use the friction slip ratchet if there is one on the instrument. Too much pressure on the knurled
2-21
4. When a micrometer is not in actual use, place it where it is not likely to be dropped. Dropping a micrometer can cause the frame to spring; if dropped, the instrument should be checked for accuracy before any further readings are taken.
5. Before a micrometer is returned to stowage, back the spindle away from the anvil, wipe all exterior surfaces with a clean, soft cloth, and coat the surfaces with a light oil. Do not reset the measuring surfaces to close contact because the protecting film of oil in these surfaces will be squeezed out.
MAINTENANCE OF MICROMETERS.—
A micrometer caliper should be checked for zero setting (and adjusted when necessary) as a matter of routine to ensure that reliable readings are being obtained. To do this, proceed as follows:
1 . Wipe the measuring faces, making sure that they are perfectly clean, and then bring the spindle into contact with the anvil. Use the same moderate force that you ordinarily use when taking a measurement. The reading should be zero; if it is not, the micrometer needs further checking.
2. If the reading is more than zero, examine the edges of the measuring faces for burrs. Should burrs be present, remove them with a small slip of oilstone; clean the measuring surfaces again, and then recheck the micrometer for zero setting.
3. If the reading is less than zero, or if you do not obtain a zero reading after making the correction described above, you will need to adjust the spindle-thimble relationship. The method for setting zero differs considerably between makes of micrometers. Some makes have a thimble cap which locks the thimble to the spindle; some have a special rotatable sleeve on the barrel that can be unlocked; and some have an adjustable anvil.
Methods for Setting Zero. — To adjust the THIMBLE-CAP TYPE, back the spindle away from the anvil, release the thimble cap with the small spanner wrench provided for that purpose, and bring the spindle into contact with the anvil. Hold the spindle firmly with one hand and rotate the thimble to zero with the other; after zero relation has been established, rotate the spindle counterclockwise to open the micrometer, and then tighten the thimble cap. After tightening the
To adjust the ROTATABLE SLEEVE TYPE, unlock the barrel sleeve with the small spanner wrench provided for that purpose, bring the spindle into contact with the anvil, and rotate the sleeve into alignment with the zero mark on the thimble. After completing the alignment, back the spindle away from the anvil, and retighten the barrel sleeve locking nut. Recheck for zero setting, to be sure you did not disturb the thimble-sleeve relationship while tightening the lock nut.
To set zero on the ADJUSTABLE ANVIL TYPE, bring the thimble to zero reading, lock the spindle if a spindle lock is provided, and loosen the anvil lock screw. After you have loosened the lock screw, bring the anvil into contact with the spindle, making sure that the thimble is still set on zero. Tighten the anvil setscrew lock nut slightly, unlock the spindle, and back the spindle away from the anvil; then lock the anvil setscrew firmly. After locking the setscrew, check the micrometer for zero setting to make sure you did not move the anvil out of position while you tightened the setscrew.
The zero check and methods of adjustment of course apply directly to micrometers that will measure to zero; the PROCEDURE FOR LARGER MICROMETERS is essentially the same except that a standard must be placed between the anvil and the spindle in order to get a zero measuring reference. For example, a 2-inch micrometer is furnished with a 1-inch standard. To check for zero setting, place the standard between the spindle and the anvil and measure the standard. If zero is not indicated, the micrometer needs adjusting.
Testing for and Correcting Errors By the Use Of Standards. — A micrometer must be tested from time to time for uneven wear of measuring threads and for concave wear of the measuring faces because these defects are not detectable by zero-setting checks. The test for uneven internal wear can be made by measuring a flat-surfaced standard; the test for concavity of measuring faces, by measuring a cylindrical disk-shaped standard.
The procedure for making these tests and correcting the defects which are found is as follows: First, check the micrometer for zero setting and adjust as necessary. Then take measurements of several different size gauge blocks or other accurate standards. If the
2-22
is muiuaieu, anu me nuuiuiiieiei be adjusted. Adjustment is made with the thread wear compensating nut, located inside the thimble assembly. After you complete the gauge block test, measure several cylindrical standards of different sizes. Discrepancies between micrometer readings and the marked (actual) sizes of the standards indicate that the measuring surfaces are concave. You can correct this condition by lapping the measuring faces on a true flat surface. After lapping the faces of the micrometer, reset the instrument for zero reading and measure the cylindrical standards again.
Inside Micrometers.— These instruments can be checked for zero setting adjusted in about the same way as a micrometer caliper; the main difference in the method of testing is that an accurate micrometer caliper is required for transferring readings to and from the standard when an inside micrometer is being checked.
Micrometers of all types should be dis- assembled periodically for cleaning and lubrica- tion of internal parts. When this is done, each part should be cleaned in noncorrosive solvent, completely dried, and then given a lubricating coat of watchmaker's oil or a similar light oil.
Vernier Gauges
Vernier gauges also require careful handling and proper maintenance if they are to remain accurate. The following instructions apply to vernier gauges in general:
1. Always loosen a gauge into position. Forcing, besides causing an inaccurate reading, is likely to force the arms out of alignment.
neavy pressure win lorce me two scales oui 01 parallel.
3. Prior to putting a vernier gauge away, wipe it clean and give it a light coating of oil. (Perspira- tion from hands will cause the instrument to cor- rode rapidly.)
Dials
Dial indicators and other instruments that have a mechanically operated dial as part of their measurement features are easily damaged by misuse and lack of proper maintenance. The following instructions apply to dials in general:
1 . As previously mentioned, be sure that the dial you have selected to use has the range capability required. When a dial is extended beyond its design limit, some lever, small gear or rack must give to the pressure. The dial will be rendered useless if this happens.
2. Never leave a dial in contact with any surface that is being subjected to a shock (such as hammering a part when dialing it in) or an erratic and uncontrolled movement that could cause the dial to be overtraveled.
3. Protect the dial when it is not being used. Provide a storage area where the dial will not receive accidental blows and where dust, oil, and chips will not contact it.
4. When a dial becomes sticky or sluggish in operating, it may be either damaged or dirty. You may find that the pointer is rubbing the dial crystal or that it is bent and rubbing the dial face. Never oil a sluggish dial. Oil will compound the problems. Use a suitable cleaning solvent to remove all dirt and residue.
2-23
CHAPTER 3
LAYOUT AND BENCHWORK
As an MR 3 or MR 2 you will repair or assist in repairing a great many types of equipment used on ships. In addition to making replacement parts, you will disassemble and assemble equipment, make layouts of parts to be machined, and do precision work in fitting mating parts of equip- ment. This is known as benchwork and includes practically all repair work other than actual machining.
This chapter contains information that you should know to enable you to make effective repairs to equipment. A brief discussion on blueprints and mechanical drawings is included because in many repair jobs you must rely heavily on information acquired from these sources. Other sources of information that you should study for details on specific equipment include the NA VSHIPS' Technical Manual, manufacturers' technical manuals, and training manuals that have information related to the equipment on which you are working.
MECHANICAL DRAWINGS AND BLUEPRINTS
A mechanical drawing, made with special instruments and tools, gives a true representation of an object to be made, including its shape, size, description, specifications of material to be used, and method of manufacture. A blueprint is an exact duplicate of a mechanical drawing. For reference purposes, every ship is furnished blueprint copies of all important mechanical drawings used in the construction of its hull and machinery. These blueprints are usually stowed in an indexed file in the log room, damage control office, technical library, or other central location, where they will be readily available for reference.
The following paragraphs cover briefly some important points concerning working from
sketches and blueprints. They do not contain definitions of all drafting terms, or information regarding the mechanics of blueprint reading, both of which are covered in detail in the training manual, Blueprint Reading and Sketching, NAVEDTRA 10077.
Of the many types of blueprints you will use aboard ship, the simplest is the PLAN VIEW. This blueprint shows the position, location, and use of the various parts of the ship. You will use plan views to find your duty and battle stations, the sickbay, the barber shop, and other parts of the ship.
In addition to plan views, you will find aboard ship other blueprints called assembly prints, unit or subassembly prints, and detail prints. These prints show various kinds of machinery and mechanical equipment.
ASSEMBLY PRINTS show the various parts of a mechanism and how the parts fit together. Individual mechanisms, such as motors and pumps, will be shown on SUBASSEMBLY PRINTS. These show location, shape, size, and relationships of the parts of the subassembly unit. Assembly and subassembly prints are used to learn operation and maintenance of machines and equipment.
Machinery Repairmen are most interested in DETAIL PRINTS; these will give you the information required to make a new part. They show size, shape, kind of material, and method of finishing. You will find them indispensable in your work.
WORKING FROM DRAWINGS
Detail prints usually show only the individual part that you must produce. They show two or more orthographic views of the object, and
3-1
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3-2
projection shows how the part will look when it is made.
to figure 3-1 to see how each is used in blueprints.
Each drawing or blueprint has a number in the title box in the lower right-hand corner of the print. The title box also shows the part name, scale used, pattern number, material required, assembly or subassembly print number to which the part belongs, and name or initials of the persons who drew, checked, and approved the drawings. (See fig. 3-1.)
Accurate and satisfactory fabrication of a part described on a drawing depends upon how well the MR does the following:
• Correctly reads the drawing and closely observes all of its data.
• Selects the correct material.
• Selects the correct tools and instruments for laying out the job.
• Uses the baseline or reference line method of locating the dimensional points during layout, thereby avoiding cumulative errors (described later in this chapter).
• Strictly observes tolerances and allowances.
• Accurately gauges and measures the work throughout the fabricating process.
• Gives due consideration, when measuring, for expansion of the workpiece by heat generated by the cutting operations. This is especially important in checking dimensions during finishing operations, if work is being machined to close tolerance.
COMMON BLUEPRINT SYMBOLS
In learning to read machine drawings you must first become familiar with the common terms, symbols and conventions (general practice) that are normally used. The information in figures 3-2, 3-3, and 3-4 will provide the basic data that
Surface Texture
Control over the finished dimensions of a part is no longer the only factor you must consider when deciding how you will do a job. The degree of smoothness, or surface roughness, has become very important in the efficiency and life of a machine part.
A finished surface may appear to be perfectly flat; however, upon close examination with surface finish measuring instruments, the surface is found to be formed of irregular waves. On top of the waves are other smaller waves which we shall refer to as peaks and valleys. These peaks and valleys are used to determine the surface roughness measurements of height and width. The larger waves are measured to give the waviness height and width measurements. Figure 3-5 illustrates the general location of the various areas for surface finish measurements and the relation of the symbols to the surface characteristics.
Surface roughness is the measurement of the finely spaced surface irregularities, the height, width, direction, and shape of which establish the predominant surface pattern. The irregularities are caused by the cutting or abrading action of the machine tools that have been used to obtain the surface. One method of measuring the irregularities is by using special measuring instruments equipped with a tracer arm. The tracer arm has either a diamond or a sapphire contact point with a 0.0005-inch radius. As the tracer arm travels across the surface the contact point moves up and down the peaks and valleys. The movement of the contact point is amplified electrically and recorded graphically on a graduated tape. From this tape the various measurements are determined.
The basic roughness symbol is a check mark. This symbol is supplemented with a horizontal extension line above it when requirements such as waviness width, or contact area must be specified in the symbol. A drawing that shows only the basic symbol indicates that the surface finish requirements are detailed in the Notes block. The roughness height rating is placed at the top of the short leg of the check
3-3
|
VISIBLE LINES |
HEAVY UNBROKEN LINES USED TO INDICATE VISIBLE EDGES OF AN OBJECT |
; |
||||||
|
MEDIUM LINES WITH SHORT EVENLY SPACED DASHES |
1 1 |
i i i |
||||||
|
HIDDEN LINES |
||||||||
|
USED TO INDICATE CONCEALED EDGES |
r^ |
1_ |
||||||
|
CENTER LIMES |
THIN LINES MADE UP OF LONG AND SHORT DASHES ALTERNATELY SPACED AND CONSISTENT IN LENGTH USED TO INDICATE SYMMETRY ABOUT AN AXIS AND LOCATION OF CENTERS |
^k |
— |
3 3 |
||||
|
DIMENSION LINES |
1 I |
THIN L INES TERMIMATED WITH ARROW HEADS AT EACH END USED TO INDICATE DISTANCE MEASURED |
~~1 r^ |
••— ••— • |
-*• -»• |
|||
|
THIN UNBROKEN LINES |
- |
-» |
||||||
|
LINES |
USED TO INDICATE EXTENT OF DIMENSIONS |
|||||||
|
LEADER |
dl |
THIN LINE TERMINATED WITH ARROW. HEAD OR DOT ATONE END USED TO INDICATE A PART, DIMENSION OR OTHER REFERENCE |
r '. X 20 THD. |
|
y |
|||
|
PHANTOM OR DATUM LINE |
MEDIUM SERIES OF ONE LONG DASH AND TWO SHORT DASHES EVENLY SPACED ENDING Wl TH L ONG DASH USED TO INDICAT E ALTERNATE POSITION OF PARTS, REPEAT ED DETAIL OR TO INDICATE A DATUM PLANE |
r |
|
|
BREAK (LONG) |
-V- -vy- |
THIN SOLID RUL ED LINES WITH FREEHAND ZIG-ZAGS USED TO REDUCE SIZE OF DRAWING REQUIRED TO DELINEATE OBJECT AND REDUCE DETAIL |
|
|
i — \ — i |
|||
|
1 v 1 |
|||
|
BREAK (SHORT) |
1 |
THICK SOL ID FREE HAND LINES USED TO INDICATE A SHORT BREAK |
|
|
~u |
|||
|
CUTTINGOR VIEWING PLANE |
r i 1 1 |
THICK SOLID LINES WITH ARROWHEAD TO INDICATE DIRECTION IN WHICH SECTION OR PLANE IS VIEWED OR TAKEN |
EflTWTEl |
|
VIEWING PLANE OPTIONAL |
|||
|
CUTTING PLANE FOR COMPLEX OR OFFSET VIEWS |
*-i i (% %vi i .4-j |
THICK SHORT DASHES USED TO SHOW OFFSET WITH ARROW. HEADS TO SHOW DIRECTION VIEWED |
-4", S^*~^fc*. P"/^ Ni./ \nm •+• |
Figure 3-2. — Line characteristics and conventions for MIL-STD drawing.
3-4
|
-^ |
ANGULARITY |
|
|
1 |
PERPENDICULARITY |
|
|
II |
PARALLELISM |
|
|
© |
CONCENTRICITY |
|
|
^ |
TRUE POSITION |
|
|
0 |
ROUNDNESS |
|
|
•=- |
SYMMETRY |
|
|
(M) |
(MMO MAXIMUM MATERIAL CONDITION |
|
|
®(RFS) REGARDLESS OF FEATURE SIZE |
||
|
B3 |
DATUM IDENTIFYING |
SYMBOL |
Figure 3-3.— Geometric characteristic symbols.
\
-SYMBOL (THIS FEATURE SHALL BE PERPENDICULAR)
A [ B
MR
DATUM REFERENCE (TO DATUM A)
REFERENCE
TO TWO
TOLERANCE D*™*' (WITHIN .001 ' REGARDLESS OF FEATURE SIZE)
J. A .001
-B-
Figure 3-4. — Feature control symbol incorporating datum reference.
rROUGHNESS HEIGHT
TYPICAL FLAW (SCRATCH)
WAV I NESS HEIGHT (INCHES)
•LAY (DIRECTION OF DOMINANT PATTERN)
WAVINESS WIDTH (INCHES)
SURFACE ROUGHNESS WIDTH
ROUGHNESS -WIDTH CUTOFF (INCHES)
WAVINESS HEIGHT (INCHES)'
ROUGHNESS HEIGHT RATING
WAVJNESS WIDTH (INCHES)
ROUGH NESS -WIDTH CUTOFF (INCHES)
LAY
SURFACE ROUGHNESS WIDTH
(INCHES)
Figure 3-5. — Relation of symbols to surface characteristics.
3-5
63
63
63
Figure 3-6.— Symbols used to indicate surface roughness, waviness, and lay.
mium pciuussiuic luugmiess iicigiu ictimg;
if two are shown, the top number is the maximum (part B, fig. 3-6). A point to remember is that the smaller the number in the roughness height rating, the smoother the surface.
Waviness height values are shown directly above the extension line at the top of the long leg of the basic check (part C, fig. 3-6). Waviness width values are placed just to the right of the waviness height values (part D, fig. 3-6). Where minimum requirements
LAY SYMBOL
DESIGNATION
EXAMPLE
LAY PARALLEL TO THE BOUNDARY LINE REPRESENT- ING THE SURFACE TO WHICH THE SYMBOL APPLIES.
DIRECTION
OF TOOL
MARKS
_L
LAY PERPENDICULAR TO THE BOUNDARY LINE REPRE- SENTING THE SURFACE TO WHICH THE SYMBOL APPLIES.
DIRECTION
OF TOOL
MARKS
X
LAY ANGULAR IN BOTH DIRECTIONS TO BOUNDARY LINE REPRESENTING THE SURFACE TO WHICH SYMBOL APPLIES.
DIRECTION
OF TOOL
MARKS
M
LAY MULTIDIRECTIONAL
C
LAY APPROXIMATELY CIRCULAR RELATIVE TO THE CENTER OF THE SURFACE TO WHICH THE SYMBOL APPLIES.
R
LAY APPROXIMATELY RADIAL RELATIVE TO THE CENTER OF THE SURFACE TO WHICH THE SYMBOL APPLIES.
P
LAY PARTICULATE, NON-DIRECTIONAL, OR PROTUBERANT
3 The "P" symbol is not currently shown in ISO Standards. American National Standards Committee B46 (Surface Texture) has proposed its inclusion in ISO 1302-"Methods of indicating surface texture on drawings."
Figure 3-7.— Symbols indicating the direction of lay.
3-6
\JJL Lilt
E, fig. 3-6). Any further surface finish requirements that would have been shown in that location, such as waviness width or height, will be shown in the Notes block of the drawing.
Lay is the direction of the predominant surface pattern produced by the tool marks. The symbol indicating lay is placed to the right and slightly above the point of the surface roughness symbol as shown in part F of figure 3-6. (Figure 3-7 shows the seven symbols that indicate the direction of lay.)
The roughness width value is shown just to the right of and parallel to the lay symbol. The roughness width cutoff is placed immediately below the extension line and to the right of the
In the past, an alpha-numeric symbol was used to indicate the degree of smoothness required on a part. This system was not very effective because no specific or measurable value was assigned to each classification of finish. A fine tool finish can mean different things to different people. Some of the more common symbols that may be found on older blueprints are shown in table 3-1.
Your shop may not have the delicate and expensive instruments used to measure the irregularities of a surface although some of the larger and more fully equipped repair facilities will have them. There are roughness comparison specimens available today that will serve all but the most critical applications. These can be small plastic or metal samples, representing various roughness heights in several lay patterns.
Table 3-1.— Former Finish Designations
|
Preferred Symbols |
Meaning |
Alternate Symbols |
|||
|
F, |
Rough Tool Finish |
V, |
Fr. |
FIN. |
TF. |
|
F2 |
Fine Tool Finish |
V2 |
F. |
Fs. |
SF. |
|
F3 |
Grind Finish |
V3 |
Fg. |
Gr. |
|
|
F4 |
Polish |
V4 |
Bf. |
Buff |
|
|
Fs |
Drill |
vs |
Dr. |
||
|
F6 |
Ream |
V6 |
Rm. |
||
|
F7 |
File Finish |
V7 |
ff. |
Ff. |
|
|
F8 |
Scrape |
V8 |
scr. |
||
|
F9 |
Spot Face |
V9 |
|||
|
Finish All Over |
F.A.O. |
f.a.o. |
3-7
Figure 3-8 gives a sampling of some roughness height values that can be obtained by the different machine operations that you will encounter. Use it as an estimating tool only, as it has the same shortcomings as the "F" values in table 3-1.
UNITS OF MEASUREMENTS
Accuracy is the trademark of the Machinery Repairman, and it is to your advantage to always strive for the greatest amount of accuracy. You can work many hours on a project and if it is not accurate, you will oftentimes have to start over. With this thought in mind, study carefully the following information about both the English and the metric systems of measurement.
English System
The inch is the basic (or smallest whole) unit of measurement in the English system. Parts of the inch must be expressed as either common fractions or decimal fractions. Examples of
common fractions are 1/2, 1/4, 1/8, 1/16, 1/32, and 1/64. Decimal fractions can be expressed with a numerator and denominator (1/10, 1/100, 1/1000, etc.,) but in most machine shop work and on blueprints or drawings they are expressed in decimal form such as 0.1, 0.01, and 0.001. Decimal fractions are expressed in the following manner:
One-tenth inch = 0.1 in. One-hundredth inch = 0.01 in. One-thousandth inch = 0.001 in. One ten-thousandth inch = 0.0001 in.
You will occasionally need to convert a common fraction to a decimal. This is easily done by dividing the denominator of the fraction into the numerator. As an example, the decimal equivalent of the fraction 1/16 inch is: 1 -r 16 = 0.0625 inch. A chart giving the decimal equivalents of the most common fractions is shown in Appendix I.
MACHINE OPERATION
ROUGHNESS HEIGHT (MICROINCHES) 2000 1000 500 250 125 63 32 16 8 4
FLAME CUTTING
SAWING PLANING
DRILLING MILLING
BROACHING REAMING BORING, TURNING
ROLLER BURNISHING
GRINDING
HONING
POLISHING LAPPING
SAND CASTING
Figure 3-8. — Roughness height values for machine operations.
J. •/ *••*» Q -V
this system of measurement. The basic unit of linear measurement for the metric system is the meter.
In the metric system the meter can be sub- divided into the following parts:
10 decimeters (dm)
or 100 centimeters (cm)
or 1000 millimeters (mm)
Therefore, 1 decimeter is 1/10 of a meter, 1 centimeter is 1/100 meter, and 1 millimeter is 1/1000 meter. The metric unit of measurement most often used in the machinist trade is the millimeter (mm).
If you understand the relationship of the two systems, you can convert easily from one system to the other. For example, 1 meter is equal to 39.37 inches; 1 inch is equal to 2.54 centimeters (or 25.4 millimeters). To convert from the English system to the metric system, multiply the number of inches by 2.54 (for centimeters) or 25.40 (for millimeters). As an example: 1.375 inches converted to centi- meters is 1.375 inch x 2.540 = 3.4925 cm. Further, 0.0008 inch converted to millimeters is 0.0008 inch x 25.40 = 0.0203 mm.
To convert from the metric system to the English system, divide the metric units of measure by either 2.54 (for centimeters) or 25.4 (for millimeters). As an example: 0.215 mm converted to inches is 0.215 mm -f 25.4 = 0.0084 inch.
LIMITS OF ACCURACY
You must work within the limits of accuracy specified on the drawing. A clear understanding of TOLERANCE and ALLOWANCE will help you to avoid making small, but potentially dangerous errors. These terms may seem closely related but each has a very precise meaning and application. In the following paragraphs we will point out the meanings of these terms and the importance of observing the distinction between them.
addition to the basic dimensions, an allowable variation. The amount of variation, or limit of error permissible is indicated on the drawing as plus or minus (±) a given amount, such as ±0.005; ±1/64. The difference between allowable minimum and the allowance maximum dimension is tolerance. For example, in figure 3-9:
Basic dimension = 4
Long limit = 4 1/64 Short limit = 3 63/64 Tolerance = 1/32
When tolerances are not actually specified on a drawing, fairly concrete assumptions can be made concerning the accuracy expected, by using the following principles. For dimensions that end in a fraction of an inch, such as 1/8, 1/16, 1/32, 1/64, consider the expected accuracy to be to the nearest 1/64 inch. When the dimension is given in decimal form, the following applies:
If a dimension is given as 3.000 inches, the accuracy expected is ±0.0005 inch; or if the dimension is given as 3.00 inches, the accuracy expected is ±0.005 inch. The ±0.0005 is called in shop terms, "plus or minus five ten- thousandths of an inch." The ±0.005 is called "plus or minus five thousandths of an inch."
Allowance
Allowance is an intentional difference in dimensions of mating parts to provide the desired fit. A CLEARANCE ALLOWANCE permits movement between mating parts when they are assembled. For example, when a hole with a 0.250-inch diameter is fitted with a shaft that has a 0.245-inch diameter, the clearance allowance is 0.005 inch. An INTERFERENCE ALLOW- ANCE is the opposite of a clearance allowance.
_
64
Figure 3-9.— Basic dimension and tolerance.
3-9
nidi nave ail miciiciciiLC auuwaucc. IL
Si 0.251-inch diameter is fitted into the hole identified in the preceding example, the difference between the dimensions will give an interference allowance of 0.001 inch. As the shaft is larger than the hole, force is necessary to assemble the parts.
What is the relationship between tolerance and allowance? In the manufacture of mating parts, the tolerance of each part must be controlled so that the parts will have the proper allowance when they are assembled. For example, if a hole 0.250 inch in diameter with a tolerance of 0.005 inch (±0.0025) is prescribed for a job, and a shaft to be fitted in the hole is to have a clearance allowance of 0.001 inch, the hole must first be finished within the limits and the required size of the shaft determined exactly, before the shaft can be made. If the hole is finished to the upper limit of the basic dimension (0.2525 inch), the shaft would be machined to 0.2515 inch or 0.001 inch smaller than the hole. If the dimension of the shaft were given with the same tolerance as the hole, there would be no control over the allowance between the parts. As much as 0.005-inch allowance (either clearance or interference) could result.
To provide a method of retaining the required allowance while permitting some tolerance in the dimensions of the mating parts, the tolerance is limited to one direction on each part. This single direction (unilateral) tolerance stems from the basic hole system. If a clearance allowance is required between mating parts, the hole may be larger but not smaller than the basic dimension; the part that fits into the opening may be smaller, but not larger than the basic dimension. Thus, shafts and other parts that fit into a mating opening have a minus tolerance only, while the openings have a plus tolerance only. If an interference allowance between the mating parts is required, the situation is reversed; the opening can be smaller but not larger than the basic dimension, while the shaft can be larger, but not smaller than the basic dimension. Therefore you can expect to see a tolerance such as +0.005, - 0, or +0, -0.005, but with the required value not necessarily 0.005. One way to get a better understanding of a clearance allowance, or an interference allowance, is to make a rough sketch of the piece and add dimensions to the sketch where they apply.
metal surfaces to provide an outline for machining. A layout is comparable to a single view (end, top, or side) of a part which is sketched directly on the workpiece. Any difficulty in making layouts depends on the intricacies of the part to be laid out and the number of operations required to make the part. A flange layout, for example, is relatively simple as the entire layout can be made on one surface of the blank flange. However, an intricate casting may require layout lines on more than one surface. This requires careful study and concentration to ensure that the layout will have the same relationships as those shown on the drawing (or sample) that you are using.
When a part must be laid out on two or more surfaces, you may need to lay out one or two surfaces and machine them to size before using further layout lines. This prevents removal of layout lines on one surface while you are machining another. In other words, it would be useless to lay out the top surface of a part and machine off the layout lines while cutting the part to the layout lines of an end surface.
Through the process of computing and transferring dimensions, you will become familiar with the relationship of the surfaces. Under- standing this relationship will benefit you in planning the sequence of machining operations.
You should be able to hold the dimensions of a layout to within a tolerance of 1/64 inch. Sometimes you must work to a tolerance of even less than that.
A layout of a part is made when the directional movement or location of the part is controlled by hand or aligned visually without the use of precision instruments (such as when work is done on bandsaws or drill presses.) In cutting irregular shapes on shapers, planers, lathes, or milling machines, layout lines are made, and the tool or work is guided by hand. In making a part with hand cutting tools, layout is essential.
Mechanical drawing and layout are closely related subjects; knowledge of one will help you to understand the other. A knowledge of general mathematics, trigonometry, and geometry, as well as the selection and use of the required tools is necessary in doing jobs related to layout and mechanical drawing. Study Mathematics, Volume 7, NAVEDTRA 10069; Mathematics, Volume II, NAVEDTRA 10071; Tools and Their Uses, NAVEDTRA 10085, and Blueprint Reading and
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MATERIALS AND EQUIPMENT
A scribed line on the surface of metal is usually hard to see; therefore, a layout liquid is used to provide a contrasting background. Commercially prepared layout dyes or inks are available through the Navy supply system. Chalk can be used, but it does not stick to a finished surface as well as layout dye. The commonly used layout dyes color the metal surface with a blue or copper tint. A line scribed on this colored surface reveals the color of the metal through the background.
The tools generally used for making layout lines are the combination square set, machinist's square, surface gauge, scribe, straightedge, rule, divider, and caliper. Tools and equipment used in setting up the part to be laid out are surface plates, parallel blocks, angle plates, V-blocks, and sine bar. Surface plates have very accurately scraped flat surfaces. They provide a mounting table for the work to be laid out so that all lines in the layout can be made to one reference surface. Angle plates are used to mount the work at an angle to the surface plate. Angle plates are commonly used when the lines in the layout are at an angle to the reference surface. These plates may be fixed or adjustable; fixed angle plates are more accurate because one surface is machined to a specific angle in relation to the base. Adjustable angle plates are convenient to use because the angular mounting surface can be adjusted to meet the requirements of the job. V- blocks are used for mounting round stock on the surface plate. Parallel blocks are placed under the work to locate the work at a convenient height.
The sine bar is a precision tool used for determining angles which require accuracy within 5 minutes of arc. The sine bar may be used to check angles or to establish angles for layout and inspection work. The sine bar must be used in conjunction with a surface plate and gauge blocks if accuracy is to be maintained. Use of the sine bar will be covered later in this chapter.
Toolmaker's buttons (figure 3-10) are hard- ened and ground cylindrical pieces of steel, used to locate the centers of holes with extreme accuracy. You may use as many buttons as necessary on the same layout by spacing them the proper distance from each other with gauge blocks.
Many other special tools, which you may make, will be useful in obtaining layouts that are
CAP SCREW
BUTTON
WORK
Figure 3-10. — Toolmaker's buttons and their application.
accurate and easily done. Transfer screws and punches for laying out from a sample are two that you can use on many jobs and save time in doing the job.
LAYOUT METHODS
To ensure complete accuracy when making layouts, establish a reference point or line on the work. This line, called the baseline, is located so you can use it as a base from which to measure dimensions, angles, and lines of the layout. You can use a machined edge or centerline as a reference line. Circular layouts, such as flanges, are usually laid out from a center point and a diameter line.
You can hold inaccuracy in layouts to a minimum by using the reference method because errors can be made only between the reference line and one specific line or point. Making a layout by referencing each line or point to the preceding one can cause you to compound any error, thus creating an inaccurate layout.
Making a layout on stock that has one or more machine finished surfaces usually is easy. Laying out a casting, however, presents special problems because the surfaces are too rough and not true enough to permit the use of squares, surface plates, or other mounting methods with any degree of accuracy. A casting usually must be machined on all surfaces. Sufficient material must be left outside the layout line for truing up the surface by machining. For example, a casting might have only 1/8-inch machining allowance on each surface (or be a total of 1/4-inch oversize). It is obvious in this example that taking more than 1/8 inch off any surface would mean the loss of the casting. The layout procedure is especially
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must be within the machining allowance on all surfaces.
Making Layout Lines
The following information applies to practi- cally all layouts. Layout lines are formed by using a reference edge or point on the stock or by using the surface plate as a base. Study care- fully the section on geometric construction as this will aid you in making layouts when a reference edge of the stock or a surface plate mounting of the stock cannot be used.
LINES SQUARE OR PARALLEL TO
EDGES. — When scribing layout lines on sheet metal, hold the scratch awl, or scribe, as shown in figure 3-11, leaning it toward the direction in which it will be moved and away from the straightedge. This will help scribe a smooth line which will follow the edge of the straightedge, template, or pattern at its point of contact with the surface of the metal.
To scribe a line on stock with a combination square, place the squaring head on the edge of
square with the edge of the stock against which the squaring head is held; that is, the angle between the line and the edge will be 90°.
To draw lines parallel to an edge using a combination square, extend the blade from the squaring head the required distance, such as the 2-inch setting shown in figure 3-13. Secure the blade at this position. Scribe a line parallel to the edge of the stock by holding the scratch awl, 01 scribe, at the end of the blade as you move the square along the edge. All lines so scribed, with different blade settings, will be parallel to the edge of the stock and parallel to each other.
Figure 3-13.— Laying out parallel lines with a combinatioi square.
Figure 3-11. — Using a scribe.
Figure 3-12. — Using the combination square.
Figure 3-14. — Laying out a parallel line with a hermaphrodil caliper.
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in figure 3-14, so the curved leg maintains contact with the edge while the other leg scribes the line. Hold the caliper so that the line will be scribed at the desired distance from the edge of the stock.
FORMING ANGULAR LINES.— To lay out
a 45 ° angle on stock, using a combination square, place the squaring head on the edge of the stock, as shown in figure 3-15, and draw the line along either edge of the blade. The line will form a 45 ° angle with the edge of the stock against which the squaring head is held.
To draw angular lines with the protractor head of a combination square, loosen the adjusting screw and rotate the blade so the desired angle
Figure 3-15. — Laying out a 45° angle.
PARALLEL UNES
SCRIBER
TRUE EDGE
is 60°. Tighten the screw to hold the setting.
Hold the body of the protractor head in contact with the true edge of the work with the blade resting on the surface. Scribe the lines along the edge of the blade on the surface of the work. The angle set on the scale determines the angle laid out on the work. All lines drawn with the same setting, and from the same true edge of the work, will be parallel lines.
Use the center head and rule as illustrated in figure 3-17 to locate the center of round stock. To find the center of square and rectangular shapes, scribe straight lines from opposite corners of the workpiece. The intersection of the lines locates the center.
LAYING OUT CIRCLES AND IRREG- ULAR LINES.— Circles or segments of circles are laid out from a center point. To ensure accuracy, prick-punch the center point to keep the point of the dividers from slipping out of position.
To lay out a circle with a divider, take the setting of the desired radius from the rule, as shown in figure 3-18. Note that the 3-inch setting
Figure 3-17. — Locating the center of round stock.
Figure 3-16. — Laying out angular lines.
Figure 3-18.— Setting a divider to a dimension.
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is being taken AWAY from the end of the rule. This reduces the chance of error as each point of the dividers can be set on a graduation. Place one leg of the divider at the center of the proposed circle, lean the tool in the direction it will be rotated, and rotate it by rolling the knurled handle between your thumb and index finger. (A of fig. 3-19.)
Figure 3-21.— Angle plate.
Figure 3-19. — Laying out circles.
BULKHEAD
SURFACE PLATE
Figure 3-20. — Laying out an irregular line from a surface.
Figure 3-22.— Setting and using a surface gauge.
trammel points.
To lay out a circle with trammel points, hold one point at the center, lean the tool in the direction you plan to move the other point, and swing the arc, or circle, as shown in B of figure 3-19.
To transfer a distance measurement with trammel points, hold one point as you would for laying out a circle and swing a small arc with the other point opened to the desired distance.
Scribing an irregular line to a surface is a skill used in fitting a piece of stock, as shown in figure 3-20, to a curved surface. In A of figure 3-20 you see the complete fit. In B of figure 3-20 the divider has scribed a line from left to right. When scribing horizontal lines, keep legs of the divider plumb (one above the other). When scribing vertical lines, keep the legs level. To scribe a line to an irregular surface, set the divider so that one leg will follow the irregular surface and the other leg will scribe a line on the material that is being fitted to the irregular surface. (See B of fig. 3-20.)
USING THE SURFACE PLATE.— The
surface plate is used with such tools as parallels, squares, V-blocks, surface gauges, angle plates, and sine bar in making layout lines. Angle plates similar to the one shown in figure 3-21 are used to mount work at an angle on the surface plate. To set the angle of the angle plate, use a protractor and rule of the combination square set or use a vernier protractor.
Part A of figure 3-22 shows a surface gauge V-block combination used in laying out a piece of stock. To set a surface gauge for height, first
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3-22. Secure the scale so the end is in contact with the surface of the plate. Move the surface gauge into position.
USING THE SINE BAR.— A sine bar is a precisely machined tool steel bar used in conjunction with two steel cylinders. In the type shown in figure 3-23, the cylinders establish a precise distance of either 5 inches or 10 inches from the center of one to the center of the other, depending upon the model used. The bar itself has accurately machined parallel sides, and the axes of the two cylinders are parallel to the adjacent sides of the bar within a close tolerance. Equally close tolerances control the cylinder roundness and freedom from taper. The slots or holes in the bar are for convenience in clamping workpieces to the bar. Although the illustrated bars are typical, there is a wide variety of specialized shapes, widths, and thicknesses.
The sine bar itself is very easy to set up and use. You do need to have a basic knowledge of trigonometry to understand how it works. When a sine bar is set up, it always forms a right triangle. A right triangle has one 90° angle. The base of the triangle, formed by the sine bar, is the surface plate, as shown in figure 3-23. The side opposite is made up of the gauge blocks that raise one end of the sine bar. The hypotenuse is always formed by the sine bar, as shown in figure 3-23. The height of the gauge block setting may be found in two ways. The first method is to multiply the sine of the angle needed by the length of the sine bar. The sine of the angle may be found in any table of natural trigonometric functions. For
HYPOTENUSE
SINE BAR (HYPOTENUSE)
GAGE BLOCKS (SIDE OPPOSITE)
GIVEN ANGLE
SIDE ADJACENT
SURFACE PLATE (SIDE ADJACENT)
Figure 3-23.— Setup of the sine bar.
3-15
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find the sine of 30 °5'. Then multiply the sine value by 10 inches: 0.50126 x 10 = 5.0126, to find the height of the gauge blocks. The second method is to use a table of sine bar constants. These tables give the height setting for any given angle (to the nearest minute) for a 5-inch sine bar. Tables are not normally available for 10-inch bars because it is just as easy to use the sine of the angle and move the decimal point one place to the right. Although sine bars have the appearance of being rugged, they should receive the same care as gauge blocks. Because of the nature of their use in conjunction with other tools or parts that are heavy, they are subject to rough usage. Scratches, nicks, and burrs should be removed or repaired. They should be kept clean from abrasive dirt and sweat and other corrosive agents. Regular inspection of the sine bar will locate such defects before they are able to affect the accuracy of the bar. When sine bars are stored for extended periods, all bare metal surfaces should be cleaned and then covered with a light film of oil. Placing a cover over the sine bar will further prevent accidental damage and discourage corrosion.
GEOMETRIC CONSTRUCTION OF LAY- OUT LINES. — Sometimes you will need to scribe a layout that cannot be made using conventional layout methods. For example, you cannot readily make straight and angular layout lines on sheet metal with irregular edges by using a combination square set; neither can you mount sheet metal on angle plates in a manner that permits scribing angular lines. Geometric construction is the answer to this problem.
Use a divider to lay out a perpendicular FROM a point TO a line, as shown in figure 3-24. Lightly prick-punch point C, then swing any arc
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at a point such as F. Place a straightedge on points C and F. The line drawn along this straightedge from point C to line AB will be perpendicular (90°) to line AB.
Use a divider to lay out a perpendicular FROM a point ON a line, as shown in figure 3-25. Lightly prick-punch the point identified in the figure as C on line AB. Then set the divider to any distance to scribe arcs which intersect AB at D and E with C as the center. Punch C and E lightly. With D and E used as centers and with the setting of the divider increased somewhat, scribe arcs which cross at points such as F and G. The line drawn through F and G will pass through point C and be perpendicular to line AB.
To lay out parallel lines with a divider, set the divider to the selected dimension. Then referring to figure 3-26, from any points (prick-punched) such as C and D on line AB, swing arcs EF and GH. Then draw line IJ tangent to these two arcs and it will be parallel to line AB and at the selected distance from it.
Bisecting an angle is another geometric construction with which you should be familiar. Angle ABC (fig. 3-27) is given. With B as a center, draw an arc cutting the sides of the angle at D and E. With D and E as centers, and with a radius greater than half of arc DE, draw arcs intersecting at F. A line drawn from B through point F bisects the angle ABC.
Figure 3-25.— Layout of a perpendicular from a point on a line.
Figure 3-24. — Layout of a perpendicular from a point to a line.
AC D B
Figure 3-26. — Layout of a parallel line.
3-16
Figure 3-27.— Bisecting an angle.
Laying Out Valve Flange Bolt Holes
Before describing the procedure for making valve flange layouts, we need to clarify the terminology used in the description. Figure 3-28 shows a valve flange with the bolt holes marked on the bolt circle. The straight-line distance between the centers of two adjacent holes is called the PITCH CHORD. The bolt hole circle itself is called the PITCH CIRCLE. The vertical line across the face of the flange is the VERTICAL BISECTOR, and the horizontal line across the face of the flange is the HORIZONTAL BISECTOR.
PITCH CIRCLE
HORIZONTAL- BISECTOR
VERTICAL BISECTOR
PITCH CHORD
SNUGLY FITTING WOOD PLUG
Figure 3-28. — Flange layout terminology.
LIIC same as me
chord between any other two adjacent holes. Note that the two top holes and the two bottom holes straddle the vertical bisector; the vertical bisector cuts the pitch chord for each pair exactly in half. This is the standard method of placing the holes for a 6-hole flange. In the 4-, 8-, or 12-hole flange, the bolt holes straddle both the vertical and horizontal bisectors. This system of hole place- ment permits a valve to be installed in a true vertical or horizontal position, provided, of course, that the pipe flange holes are also in standard location on the pitch circle. Before proceeding with a valve flange layout job, find out definitely whether the holes are to be placed in the standard position. If you are working on a "per sample" job, follow the layout of the sample.
Assuming that you have been given informa- tion concerning the size and number of holes and the radius of the pitch circle, the procedure for setting up the layout for straight globe or gate valve flanges is as follows:
1. Fit a fine grain wood plug into the opening in each flange. (See fig. 3-28.) The plug should fit snugly and be flush with the face of the flange.
2. Apply layout dye to the flange faces, or, if dye is not available, rub chalk on the flange faces to make the drawn lines clearly visible.
3. Locate the center of each flange with a surface gauge, or with a center head and rule combination, if the flange diameter is relatively small. (See part A fig. 3-22 and fig. 3-17.) After you have the exact center point located on each flange, mark the center with a sharp prick-punch.
4. Scribe the pitch or bolt circle, using a pair of dividers. Check to see that the pitch circle and the outside edge of the flange are concentric.
5. Draw the vertical bisector. This line must pass through the center point of the flange and must be visually located directly in line with the axis of the valve stem. (see fig. 3-28.)
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6. Draw the horizontal bisector. This line must also pass through the center point of the flange and must be laid out at a right angle to the vertical bisector. (See fig. 3-28 and fig. 3-25.)
Up to this point, the layout is the same for all flanges regardless of the number of holes. Beyond this point, however, the layout differs with the number of holes. The layout for a 6-hole flange is the simplest one and will be described first.
SIX-HOLE FLANGE.— Set your dividers exactly to the dimension of the pitch circle radius. Place one leg of the dividers on the point where the horizontal bisector crosses the pitch circle on the right-hand side of the flange, point (1) in part A of figure 3-29, and draw a small arc across the pitch circle at points (2) and (6). Next, place one leg of the dividers at the intersection of the pitch circle and horizontal bisector on the left-hand side of the flange point (4), and draw a small arc across the pitch circle line at points (3) and (5). These points, (1 to 6), are the centers for the holes. Check the accuracy of the pitch chords. To do this, leave the dividers set exactly as you had them set for drawing the arcs. Starting from the located center of any hole, step around the circle with the dividers. Each pitch chord must be equal to the setting of the dividers; if it is not, you have an
error in hole mark placement that you must correct before you center punch the marks for the holes. After you are sure the lay- out is accurate, center punch the hole marks and draw a circle of appropriate size around each center-punched mark and prick-punch "witness marks" around the circumference as shown in part B of figure 3-29. These witness marks will be cut exactly in half by the drill to verify a correctly located hole.
FOUR-HOLE FLANGE.— Figure 3-30 shows the development for a 4-hole flange layout. Set your dividers for slightly more than half the distance of arc AB, and then scribe an intersecting arc across the pitch circle line from points A, B, C, and D, as shown in part A of figure 3-30. Next, draw a short radial line through the point of inter- section of each pair of arcs as shown in part B. The points where these lines cross the pitch circle, (1), (2), (3), and (4), are the centers for the holes. To check the layout for accuracy, set your divider for the pitch between any two adjacent holes and step around the pitch circle. If the holes are not evenly spaced, find your error and correct it. When the layout is correct, follow the center-punching and witness-marking procedure described for the 6-hole flange layout.
"WITNESS MARKS"
Figure 3-29. — Development of a 6-hole flange.
me same memo a as aescnoea lor locaung poim
(1) in the 4-hole layout. Then divide arc AE in half by the same method. The midpoint of arc AE is the location for the center of hole (1). (see part A of fig. 3-31.) Next, set your dividers for distance A (1), and draw an arc across the pitch circle line from A at point (8); from B at points
(2) and (3); from C at (4) and (5); and from D at (6) and (7). (see part B of fig. 3-31.) Now set your calipers for distance AE and
MATHEMATICAL DETERMINATION OF PITCH CHORD LENGTH.— In addition to the geometric solutions given in the preceding paragraphs, the spacing of valve flange bolt hole centers can be determined by simple multiplica- tion, provided a constant value for the desired number of bolt holes is known. The diameter of the pitch circle multiplied by the constant equals the length of the pitch chord. The
Figure 3-30.— Four-hole flange development.
Figure 3-31. — Eight-hole flange development.
3-19
Here is an example of the use of the table. Suppose a flange is to have 9 bolt holes laid out on a pitch circle with a diameter of 10 inches. From the table, select the constant for a 9-hole flange. The pitch diameter (10 inches) multiplied by the appropriate constant (.342) equals the length of the pitch chord (3.420 inches). Set a pair of dividers to measure 3.420 inches, from point to point, and step off around the circumference of the pitch circle to locate the centers of the flange bolt holes. Note, however, that the actual placement of the holes in relation to the vertical and horizontal bisectors is determined separately. (This is of no concern if the layout is for an unattached pipe flange rather than for a valve flange.)
BENCHWORK
In this chapter, we will consider benchwork related to repair work, other than machining, in restoring equipment to an operational status. In repairing equipment, benchwork progresses in several distinct steps: obtaining information, disassembly of the equipment, inspection for defects, repair of defects, reassembly, and testing.
Table 3-2. — Constants for Locating Centers of Flange bolt Holes
No. bolt holes
9
10 11 12 13 14 15 16 17 18 19 20
Constant
0.866 .7071 .5879
.3827 .342
,2588
,2079
.195
.184
possible sources for this information. Job orders generally give brief descriptions of the equipment and the required repair. Manufacturers' technical manuals and blueprints give detailed information on operational characteristics and physical descriptions of the equipment. Operators can provide information on specific techniques of operation and may furnish clues as to why the equipment failed. The leading petty officer of your shop can provide valuable information on repair techniques, and can help you interpret the information. Use these sources of information to become familiar with the equipment before attempting the actual repair work. If you are thoroughly acquainted with the equipment, you will not have to rely on trial and error methods which are time consuming and some- times questionable in effectiveness.
There are specific techniques that can be used in assembly and disassembly of equipment which will improve the effectiveness of a repair job. Whenever you repair equipment, you should note such things as fastening devices, fits between mating parts, and the uses of gaskets and packing. Noting the positions of parts in relation to mating parts or the unit as a whole is extremely helpful in ensuring that the parts are in correct locations and positions when the unit is reassembled.
Inspecting the equipment before and during the repair procedure is necessary to determine causes of defects or damage. The renewal or replacement of a broken or worn part of a unit may give the equipment an operational status. Eliminating the cause of damage prevents recurrence.
Repairs are made by replacement of parts, by machining the parts to new dimensions, or by using handtools to overhaul and recondition the equipment. Handtools are used in the repair procedure in jobs such as filing and scraping to true surfaces and in removing burrs, nicks, and sharp edges.
It is often said that a repair job is incomplete until the repaired equipment has been tested for satisfactory operation. How equipment is tested depends on the characteristics of the equipment. In some cases testing facilities are available in the shop. When these facilities are not available, the unit may be placed back in operation and tested by normal use.
3-20
mucn ot me equipment tnat you are required to disassemble, repair, and reassemble. You must, therefore, use techniques that will aid you in remembering the position and location of parts in relatively intricate mechanisms. The following information applies in general to assembly and disassembly of any equipment.
Equipment should be disassembled in a clean, well-lighted work area. With plenty of light, small parts are less likely to be misplaced or lost, and small but important details are more easily noted. Cleanliness of the work area, as well as the proper cleaning of the parts as they are removed, decreases the possibility of damage due to foreign matter when the parts are reassembled.
Before starting any disassembly job, select the tools and parts you think you will need and take them to the work area. This will permit you to concentrate on the work without unnecessary interruptions during the disassembly and re- assembly processes.
Have a container at hand for holding small parts to prevent their loss. Use tags or other methods of marking the parts to identify the unit from which they are taken. Doing this prevents mixing parts of one piece of equipment with parts belonging to another similar unit, especially if several pieces of equipment are being repaired in the same area. Use a scribe or prick-punch to mark the relative positions of mating parts that are required to mate in a certain position. (See fig. 3-32.) Pay close attention to details of the equipment you are taking apart and fix in your mind how the parts fit together. When you
PUNCH MARKS
JOINTS
PUNCH MARKS
Figure 3-32. — Mating parts location marks.
heavy pressure is required to separate parts. An overlooked pin, key, or setscrew that locks parts in place can cause extensive damage if pressure is applied to the parts. If hammers are required to disassemble parts, use a mallet or hammer with a soft face (lead, plastic, or rawhide) to prevent distortion of surfaces. If bolts or nuts or other parts are stuck together due to corrosion, use penetrating oil to free the parts.
PRECISION WORK
The majority of repair work that you perform will involve some amount of precision hand work of parts. Broadly defined, precision hand work to the Machinery Repairman can range from using a file to remove a burr or rough, sharp edge on a hatch dog to reaming a hole for accurately locating very close fitting parts. To accomplish these jobs, you must be proficient in the use of files, scrapers, precision portable grinders, thread cutting tools, reamers, broaches, presses and oxyacetylene torches.
Scraping
Scraping produces a surface that is more accurate in fit and smoother in finish than a surface obtained in a machining operation. It is a skill that requires a great deal of practice before you become proficient at it. Patience, sharp tools and a light "feel" are required to scrape a surface that is smooth and uniform in fit.
Some of the tools you will use for scraping will be similar to files without the serrated edges. They are available either straight or with various radii or curves for scraping an internal surface at selected points. Other scraper tools may look like a paint scraper, possibly with a carbide tip attached. You may find that a scraper that you make from material in your shop will best suit the requirements of the job at hand.
A surface plate and nondrying prussian blue are required for scraping a flat surface. Lightly coat the surface plate with blue and move the workpiece over this surface. The blue will stick to the high spots on the workpiece, revealing the
3-21
areas to be scraped. (See fig. 3-33.) Scrape the areas of the workpiece surface that are blue and check again. Continue this process until the blue coloring shows on the entire surface of the workpiece. To reduce frictional "drag" between mating finished scraped surfaces, rotate the solid surfaces so that each series of scraper cuts is made at an angle of 90° to the preceding series. This action gives the finished scraped surface a crosshatched or basket weave appearance. The crosshatched method also enables you to more easily see where you have scraped the part.
A shell-type, babbitt-lined, split bearing or a bushing often requires hand scraping to ensure a proper fit to the surface that it supports or runs on. To do this, very lightly coat the shaft (or a mandrel the same size as the shaft) with nondrying Prussian blue. Turning the bearing on the shaft (or the mandrel in the bearing) just a short distance will leave thin deposits of the bluing on the high spots in the bearing babbitt. Then lightly scrape the high spots with a scraper shaped to permit selective scraping of the high spots without dragging along the other areas. Be very careful when doing this to prevent tapering the bearing excessively in either the longitudinal or radial direction. When you have worked out all the high spots, smooth out (or replace if necessary) the bluing on the shaft or mandrel and repeat the process until you have produced an acceptable seating pattern. This job cannot be rushed and done properly at the same time. A poor seating pattern on a bearing could lead to an early failure when the bearing is placed into service.
Removal of Burrs and Sharp Edges
One of the most common injuries that occurs in machine shops is a cut or scratch caused by a
Figure 3-33.— Checking a surface.
sharp edge on a part. When a pump or other piece of machinery that has been overhauled binds or wipes with little or no operating time, an investiga- tion will often reveal a sharp edge that has peeled or broken off and jammed into an area that has very little clearance. In spite of this and other instances that cause either discomfort or additional work, the removal of burrs and sharp edges is often overlooked by the machinist. Close examination of the old part or the blueprint will sometimes indicate that a machined radius is required. Regardless of the design or use of a part, a few seconds in removing these sharp edges with a file is time well spent.
Hand Reaming
When you need a round hole that is accurate in size and smooth in finish, reaming is the process that you will probably select. There are two types of reaming processes — machine reaming and hand reaming. Machine reaming requires a drill press, lathe, milling machining or other power tool to hold and drive either the reamer or the part. Machine reaming will be covered in chapter 8. Hand reaming is more accurate and is the method you will probably use most in precision bench work.
A hand reamer has a straight shank and a square machined on its end. It is driven by hand with a tap wrench placed on the square end. Several different types of hand reamers are available, as shown in figure 3-34. Each of the different types has an application for which it is best suited and a limiting range or capability. The solid hand reamer in part A of figure 3-34 is used for general purpose reaming operations where a standard or common fractional size is required. It is made with straight, helical, or spiral flutes. A helical fluted reamer is used when an interrupted cut, such as a part with a key way through it, must be made. The helical flutes ensure a greater contact area of the cutting edges than the straight fluted reamer, preventing the reamer from hanging up on the keyway and causing chatter, oversizing and poor finishes.
The expansion reamer in B of figure 3-34 is available as either straight or helical fluted. These reamers are used when a reamed hole slightly larger than the standard size is required. Expansion reamers can be adjusted from about 0.006 inch larger for a 1/4-inch reamer to about 0.012 inch larger for a 1 1/2-inch reamer. The adjustment is made by turning the screw on the cutting end of the reamer.
SOLID HAND REAMER
D
B
TAPER PIN REAMER
EXPANSION REAMER SOLID
TAPER PIPE REAMER
EXPANSION REAMER INSERTED TOOTH
Figure 3-34. — Hand reamers.
The expansion reamer in C of figure 3-34 has a much greater range for varying its size. Each reamer is adjustable to allow it to overlap the smallest diameter of the next larger reamer. The cutting blades are the insert type and can be removed and replaced when they become dull. Adjustment is made by loosening and tightening the two nuts on each side of the blades.
The taper pin reamer in D of figure 3-34 has a taper of 1/4 inch per foot and is used to ream a hole to accept a standard size taper pin. This reamer is used most often when two parts require a definite alignment position. When drilling the hole for this reamer, it is often necessary to step drill through the part with several drills of different sizes to help reduce the cutting pressure put on the reamer. Charts which give the recommended drill sizes are available in several machinist reference books. In any case, the smallest drill used cannot be larger than the small diameter of the taper pin.
The taper pipe reamer in E of figure 3-34 has a taper of 3/4 inch per foot and is used to prepare a hole that is to be threaded with a tapered pipe thread.
The size of the rough drilled or bored hole to be hand reamed should be between 0.002 inch and about 0.015 inch (1/64) smaller than the reamer size. A smoother and more accurately reamed hole can be produced by keeping to a minimum the
amount of material that a reamer is to remove. You must be careful to keep the rough hole from being oversized or out-of-round. This is a very common problem in drilling holes, and you can prevent it only by using a correctly sharpened drill under the most closely controlled conditions possible. Information on drilling can be found in chapter 5.
Alignment of the reamer to the rough hole is a critical factor in preventing oversized, out-of- round or bell-mouthed holes. If possible, perform the reaming operation while the part is still set up for the drilling or boring operation. Insert a center in the spindle of the machine and place it in the center hole in the shank of the reamer to guide the reamer.
Another method of alignment is to fabricate a fixture with guide bushings made from bronze or a hardened steel to keep the reamer straight. When a rough casting or a part that has the reamed hole at an angle to its surface must be reamed, it is best to spot face or machine the area next to the hole so that the hole and the surface are perpendicular. This will prevent an uneven start and possibly reamer breakage. In most reaming operations, you will find that the use of a lubricant will give a better reamed hole. The lubricant or cutting fluid helps to reduce heat and friction and washes away the ships that build up on the reamer. Soluble oil will normally serve very
3-23
well; however, in some cases, a lard or sulfurized cutting oil may be required. When the reaming operation is complete, remove the reamer from the part by continuing to turn the reamer in the same direction (clockwise) and putting a slight upward pressure on it with your hand until it has cleared the hole completely. Reversing the direction of the reamer will probably result in damage to both the cutting edges and the hole.
A straight hand reamer is generally tapered on the beginning of the cutting edges for a distance approximately equal to the diameter of the reamer. You will have to consider this when you ream a hole that does not go all the way through a part.
Broaching
Broaching is a machining process that cuts or shears the material by forcing a broach through the part in a single stroke. A broach is a tapered, hardened bar, into which have been cut teeth that are small at the beginning of the tool and get progressively larger toward the end of the tool. The last several teeth will usually be the correct size of the desired shape. Broaches are available to cut round, square, triangular and hexagonal holes. Internal splines and gears and key ways can also be cut using a broach. A key way broach requires a bushing that will fit snugly in the hole of the part and has a rectangular slot in it to slide the broach through. Shims of different thicknesses are placed behind the broach to adjust the depth of the key way cut (fig. 3-35).
A broach is a relatively expensive cutting tool and is easily rendered useless if not used and handled properly. Like all other cutting tools, it should be stored so that no cutting edge is in contact with any object that could chip or dull it. Preparation of the part to be broached is as important as the broaching operation itself. The size of the hole should be such that the beginning pilot section enters freely but does not allow the broach to freely fall past the first cutting edge or tooth. If the hole to be broached has flat sides opposite each other, you need only to measure across them and allow for some error from drill- ing. The broach will sometimes have the drill size printed on it. Be sure the area around the hole to be broached is perpendicular on both the entry and exit sides.
Most Navy machine shop applications involve the use of either a mechanical or a hydraulic press to force the broach through the part. A
considerable amount of pressure is required to broach, so be sure that the setup is rigid and that all applicable safety precautions are strictly observed. A slow even pressure in pushing the broach through the part will produce the most accurate results with the least damage to the broach and in the safest manner. Do not bring the broach back up through the hole, push it on through and catch it with a soft cushion of some type. A lubricant is required for broaching most metals. A special broaching oil is best; however, lard oil or soluble oil will help to cool the tool, wash away chips and prevent particles from gall- ing or sticking to the teeth.
Hand Taps and Dies
Many of the benchwork projects that you do will probably have either an internally or an externally threaded part in the design specifica- tions. The majority of the threads cut on a bench- work project are made with either hand taps, for internally threaded parts, or hand dies for externally threaded parts. The use of these two cutting tools has come to be considered as a simple skill requiring little or no knowledge of the tools and no preplanning of the operation to be performed. It is true that the operations are simple, but only after several factors concerning the correct selection and use of the tools have been studied and practiced. Taps and dies are fast and accurate cutting tools that can make a job much easier and will produce an excellent end product. The information given in the following paragraphs will provide the general knowledge and operational factors to start you in the correct use of taps and dies.
TAPS.— Hand taps (fig. 3-36) are precision cutting tools which usually have three or four flutes and a square on the end for placing a tap wrench to turn the tap. Taps are made from either hardened carbon steel or high-speed steel and are very hard and brittle. They are easily broken or damaged when treated roughly or forced too quickly through a hole.
Taps for most of the different thread forms, described later in this manual, are available either as a standard stock item or catalog special ordered from a tap manufacturer. The information in this section concerns only the most commonly used thread forms, the Unified thread and the American National thread. Both of these thread systems have a 60-degree included angle or V form.
28.33
Figure 3-35. — Broaching a keyway on a gear.
V8-I6 NC G H4
TAPER
__D V'6NC C • •„........-
6 H4 IHUlllUni
PLUG
_-^^vw^AA^^^^^^^v^A^vvvi^
BOTTOMING
Figure 3-36.— Set of taps.
Taps usually come in a set of three for each different diameter and number of threads per inch. A taper, or starting tap (fig. 3-36), has 8 to 10 of the beginning teeth that are tapered. The taper allows each cutting edge or tooth to cut slightly deeper than the one before it. This permits an easier starting for the tap and exerts a minimum amount of pressure against the tool. The next several teeth after the taper ends are at the full designed size of the tap. They remove only a small amount of material and help to leave a fine finish on the threads. The last few teeth have a very slight back taper that allows the tap to clear the final threads cut without rubbing or binding. The plug tap has 3 to 5 of the beginning teeth tapered and the remaining length has basically the same design as the taper tap. The bottoming tap
3-25
by the tapered teeth, it is always advisable to begin the tapping operation with the taper, or starting tap. If the hole being tapped goes all the way through the material, the taper tap is usually the only one required. If the hole is a blind one, or does not go all the way through the material, all three taps will be required. The taper tap will be used first, followed by the plug tap, and the final pass will be made with the bottoming tap.
Standard Sizes and Designations. — The size of a tap is marked on the shank or the smooth area between the teeth and the square on the end. The numbers and letters always follow the same pattern and are simple to understand. As an example, the marking 3/8 - 16 NC (fig. 3-36) means that the diameter of the tap is 3/8 inch and that it has 16 threads per inch. The NC is a sym- bol indicating the thread series. In this case, the NC stands for the American National Coarse Thread Series.
Some additional common thread series symbols are NF, American National Fine; NS, American National Special; NEF, American National Extra Fine; and NPT, American National Standard Tapered pipe. A "U" placed in front of one of these symbols indicates the UNIFIED THREAD SYSTEM, a system that has the same basic form as the American National and is interchangeable with it, differing mainly in tolerance or clearance. These thread systems will be covered in more detail in chapter 9. If an LH appears on the marking after the thread series symbols, the tap is left-handed.
The next group of markings usually found on taps refers to the method of producing the threads on the tap and the tolerance of the tap. As an example, in the marking G H4 (fig. 3-36) the G indicates that the threads were ground on the tap. The greatest majority of the taps manufactured today are ground. The next symbol, H4, refers to the tolerance of the tap. The H means that the tap has a pitch diameter that is above (HIGH) the basic pitch diameter for that size tap. An L means that the pitch diameter is under (LOW) the basic pitch diameter for that size tap. The number following the H or L indicates the amount of tolerance in increments of 0.0005 inch. In the example H4, the pitch diameter is a maximum of 0.002 inch (4 x 0.0005) above the basic pitch diameter. In the case of an L, the amount is under the basic pitch diameter. A number of 1 through 10 can be found on taps. This tolerance limit
classes will be covered later in this manual.
The only difference in the size and designation markings for taps that will probably be found in Navy machine shops is in machine screw diameter taps, or numbered taps, as they are often called in the shop. Instead of the diameter being represented by a fraction, a number of 0 through 14 is used. You can easily convert these numbers to a decimal equivalent by remembering that the number 0 tap has a diameter of 0.060 inch and each tap number after that increases in diameter by 0.013 inch. As an example:
Size 0 = 0.060 inch dia.
Size 3 = 0.099 inch dia. [0.060 + 3 x 0.013]
Size 14 = 0.242 inch dia. [0.060 + 14 x 0.0131
A typical marking on a tap might be 10.24 UNC, indicating a diameter of 0.190 inch, 24 threads per inch, and a Unified National Coarse thread series.
Tapping Operations.— The first step in any successful tapping operation is the selection of the correct size tap with sharp, unbroken cutting edges on the teeth. A dull tap will require excessive force to produce the threads and increases greatly the chance of the tap breaking and damaging the part being tapped. A dull tap can also produce ragged, torn and undersize threads, leading to a damaged part.
The tap drill or the size of the hole that is made for the tap is very important if the correct fit is to be obtained. If a hole were to be drilled equal in size to the minor, or smallest, diameter of the tap, a 100% thread height would result. To tap a hole this size would require excessive pressure and breakage could occur, especially with a small tap or a material that is hard. Unless a blueprint or other design references indicate differently, a 15% thread height is usually considered adequate and is actually only about 5% less in terms of strength or holding power than a 100% thread height. In some of the less critical jobs, it is possible to have a 60% thread height without a significant loss in strength.
There are two simple formulas that you may use to calculate the tap drill size for any size tap. The simplest and the one most often used will produce a thread height of approximately 75%.
3-26
(DS = TD - ). As an example, the drill size for a 1/4 - 20 NC tap is required as follows:
Step 1: DS= 1/4 - 1/20 Step 2: DS = 0.250 - 0.050 Step 3: DS = 0.200 in.
The nearest standard size drill would then be selected to make the hole. In this case, a number
8 drill has a diameter of 0. 199 inch and a number 7 drill has a diameter of 0.201 inch. Unless the size differences are very great, it is more effective to select the larger drill size or the number 7 drill for this tap.
The second formula, although slightly more difficult, allows for a selection of the desired percentage of thread height. To use it, you must know the straight depth of the thread. You can obtain this data from various charts in handbooks for machinists or by using the formulas in chapter
9 of this manual. It is as follows: DRILL SIZE = TAP DIAMETER MINUS THE DESIRED PERCENTAGE OF THREAD HEIGHT TIMES TWICE THE STRAIGHT DEPTH. As an example, if 60% thread height is desired for a 1/4 - 20 NC tap, the drill size is figured as follows:
Step 1: DS = 1/4 - .60 x 2(0.032) Step 2: DS = 0.250 - .60 x 0.064 Step 3: DS = 0.250 - 0.038 Step 4: DS = 0.212 in.
The nearest standard size drill to 0.212 inch is a number 3 drill which has a diameter of 0.213 inch. A word of caution about drilling holes for tapping is important at this point. Even if the drill is ground perfectly, the part is rigidly clamped and the drilling machine has no looseness, the drilled hole can be expected to be oversized. In the case of the number 7 and the number 3 drills selected in the two examples given, the drilled holes will probably be approximately 0.003 to 0.004 inch oversize. You should consider this in planning the operation. Additional information on drilling holes is in chapter 5.
and shape. You MUST be sure that the part can- not vibrate loose and be thrown out of the vise or off of the drill press table. When a twist drill driven by a geared motor digs in or binds in a part, a great amount of force is exerted against the part. You could lose a finger or hand, break a leg, or worse if this happens. It is best to start the drilling operation with a small drill or a center drill (described later in this manual) by aligning the drill point as close as possible to the center punch mark you made to locate the center of the hole. When you have done this, insert the tap drill into the drilling machine or drill press and drill the hole. If the hole is very large, use a drill several sizes below the tap drill size to prevent an out- of-round or excessively oversized hole. Do NOT move the part when you make the various tool changes.
The hole is now ready to be tapped. Some taps have a center hole in the shank that will fit over the point of a center. If this is the case and the setup will allow it, place a center in the drill press without moving the part; place a tap wrench over the square shank, turn the center into the center hole on the tap wrench over the square shank, (fig. 3-37) and slowly turn the tap while applying a
CHUCK
CENTER
WORK
TAPPING WORK IN A DRILL PRESS
TAP
SQUARE
WORK
CHECKING TAP WITH A SQUARE
Figure 3-37.— Starting a tap.
3-27
slight downward pressure on the center to help guide the tap. If a center cannot be used, align the tap as close as possible by eye and make 2 or 3 turns with the tap handle. Remove the tap handle and place a good square on the surface of the part (if the part is machined flat) and bring the square into contact with one set of teeth. Do the same check on the next set of teeth in either direction around the tap (fig. 3-37). If the tap is not perpendicular or square with the surface at both points, back it out and start over. When the tap is square, begin turning the tap wrench slowly. After making two or three turns, turn the tap backwards to break the chips and help clear them from the path of the tap. Proceed with this until the tap bottoms out; then place the next tap in the set in the hole and repeat the tapping procedure. If the hole is blind, remove the taps often to clear the chips from the bottom.
It is often necessary to remove burrs from around a hole that has been tapped. Do this with a file, by slowly hand-spinning a larger twist drill in the hole, or by using a countersink.
A cutting oil should be used in most tapping operations. There are several commercial products available that greatly enhance the quality of thread produced. A heavy cutting oil with either a sulfur, mineral oil or lard oil base is available in the supply system. If no other cutting oil is available, a heavy mixture of soluble oil is acceptable.
DIES. — Hand threading dies come in various styles, including unadjustable solid square and round shaped dies and adjustable single and two- piece dies. The most common die used in Navy machine shops is the adjustable single piece or round split die (fig. 3-38). The adjustable round split die is a round disk-shaped tool which has internal threads and usually four holes or flutes that interrupt the threads and present four sets of cutting edges. The die has a groove cut completely through one side and a setscrew to allow for a small amount of expansion and contraction of the die. This feature permits an adjustment for taking a rough and a finish cut on particularly hard or tough metals and also allows for slight adjustments to obtain a close fit with a mated nut or other internally threaded part. There is a difference in the two sides of the die — the starting side has about 3 full threads tapered and the trailing side has about 1 thread tapered. To prevent damage to the die and the threads being cut, the die should always be started with the greatest taper leading. The die is held in a diestock (fig. 3-38), a tool which has a circular
ADJUSTING SCREW
ROUND SPLIT DIE A
LOCKING HOLE
THREE SCREW DIESTOCK
B Figure 3-38.— Die and diestock.
recess to hold the die and three setscrews that fit into small indentations in the outside diameter of the die.
The size of a die is usually marked on the trail- ing face (the side that is up during threading) and follows the same format as a tap. A die marked 5/8-11 NC will cut a thread that has a 5/8-inch diameter and 11 American National Coarse threads per inch. The G, H, L, and associated numbers found on a tap are not normally marked on a die because they represent a fixed tolerance and the die is adjustable.
The steps involved in threading a part with a die are similar to those for a tap. The part to be threaded should have a chamfer ground or cut on the end to help in starting the die squarely with the part. Select the correct die and insert it in the diestock with the longest tapered side opposite the square shoulder. Apply cutting oil and place the die over the part by grasping the diestock in the middle with one hand. Turn the die several turns, then look carefully at the die and the part to ensure that they are square to one another. Threads that are deeper on one side than the other indicate a misaligned die. Turn the die about three
3-28
LIUI/CIUO, J. 1>1JUI_F V
it from the part and check the fit with the part that will mate with it. Make any adjustments necessary at this time. Replace the die on the part and continue threading until you reach the desired thread length. If you are cutting the threads to a shoulder, you may turn the die over and cut the last 2 or 3 threads with the short tapered side.
Removing Broken Taps
Removing a broken tap is usually a difficult operation and requires slow, deliberate actions to remove it successfully without damaging the part involved. There is no single method that you can use in all the different circumstances you may experience. The following information describes briefly some of the methods that have proven to be effective. You will need to evaluate the particular problem and attempt removal with the method that will work best.
A tap that has broken and has at least 1/4 inch left protruding above the part can sometimes be grasped by locking pliers and removed. Use a scribe first to remove as many as of the chips as possible from the hole and the flutes of the tap. Do not use compressed air to remove the chips because there is always a chance that a small chip will be blown into either your eyes or someone's nearby. Apply penetrating oil around the threads if possible. Use a small hand grinder to shape the end of the tap to provide a good grip for the locking pliers. If they are permitted to slip on the tap, additional fragments will probably break away, giving you less surface to grasp. Apply a slow, even force. Excessive force or jerky movements will cause more damage. You may need to carefully rock or reverse the direction in which you are turning the tap in order to free it. This is especially true in beginning the removal. Use a lubricant once you have loosened the tap in the hole. When you have removed the tap, examine the hole and threads closely to ensure that no fragments of the tap or jagged threads remain to cause problems when you use another tap to finish or clean up the threads.
Another method is to use a punch and apply sharp blows to the broken tap. You will probably use this method when the tap is broken below the surface of the part. Always wear safety goggles and a face shield to protect your face and eyes from flying fragments. Do not allow anyone to stand near you while you do this type of
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away, remove it from the hole. This method will probably cause serious damage to the threaded hole when the punch strikes the threads, or an oversized condition can result from forcing the tap around in the hole. You should be sure that there is an approved method of repair or modification of the threaded hole before under- taking this method of removal.
It is sometimes possible to weld a stud to the top of a tap that is broken off below the surface. The tap diameter must be large enough for inser- tion of both the stud and the welding rod into the hole without running the risk of having the welding rod touch or splatter the threads. There are materials that can be used to help protect the threads. Unless you are an accomplished welder, do not attempt this job. Request the assistance of a Hull Maintenance Technician (HT). After the stud is welded to the tap, you can apply a more even pressure in removing the tap if you grind a square on the top of the stud so that you can use a tap wrench. The heat generated by the welding process could have expanded the tap slightly so that when it cooled and contracted, it may have loosened slightly. On the other hand, the tap may bind even more and the structure and condition of the surrounding metal may have changed.
If the tap is broken off below the surface of the part, you can use a tool called a tap extractor (fig. 3-39) to remove it. You should try this method first as it does no damage to the threads. Tap extractors are available for each of the standard diameter taps over about 3/16 inch. As you see in figure 3-38, the tap extractor has a square end for using a tap wrench and sliding prongs or fingers that fit into each of the flutes on the tap. The upper collar is secured in place by setscrews while the bottom collar is free to move. Position the bottom collar as close as
BROKEN /TAP
SLIDING PRONG
UPPER COLLAR
SQUARE SHANK
Figure 3-39.— Tap extractor.
3-29
possible to the top of the hole to prevent the sliding prongs from twisting. The best results are obtained from this tool when the sliding prongs have a minimum amount of unsupported length exposed. Apply a slow, even pressure to the tap wench in removing the tap.
In all of the methods listed, remove all chips prior to beginning the removal process. There are several methods for helping to free the tap that you can use with any of the removal methods if the particular situation lends itself to their use. As previously mentioned, you can apply penetrating oil around the threads. You can also apply a controlled heat to the area surrounding the tap to cause expansion. Be very careful to limit the heat so the tap does not begin to expand also. Since most taps are made from high-speed steel, this probably will not occur, but do not overlook the possibility. You must also consider damage to the part from heat. If the part is very big and has a large mass of metal in the immediate area, the heat will carry to the surrounding area rapidly, preventing adequate heat and expansion where it is needed.
Another method, one that you must conduct under strict safety conditions, is to apply a solution of 1 part nitric acid and 5 parts water to the threaded hole. The nitric acid solution will gradually eat away some of the surface metal and loosen the tap. After the acid solution has worked for a little while, pour it out and rinse the part thoroughly. This method is effective primarily on steel parts. When you mix the acid solution add the acid to the premeasured amount of water. The procedure of adding the acid to the water is a safety measure because some acids react violently when water is added to them. You should wear chemically resistant goggles, a face shield, rubber or plastic gloves, and an apron. Nitric acid can damage your eyes, burn your skin, and eat holes in your clothes. If any acid gets on your skin, immediately flush the skin with water for at least 15 minutes and seek medical attention. You will use nitric acid often in identifying metals. You should treat each occasion as seriously as the first, strictly observing every safety precaution.
There is one other method for removing broken taps that is used primarily on tenders, repair ships, and shore based repair activities. It involves the use of a special machine (metal disintegrator), electrodes, and a coolant. Any metal that will conduct electricity can be worked with this machine. The action of the electrode and the coolant combined create a hole through the part that is equal in size to the diameter of the
electrode. There are portable models available; however, most models either have their own cabinet or they are used in a drill press. Detailed information on this method can be found later in this manual.
Classes of Fit
The following information concerns plain cylindrical parts such as sleeves, bearings, pump wearing rings and other nonthreaded round parts that fit together. Fit is defined as the amount of tightness or looseness between two mating parts when certain allowances are designed into them. As defined earlier in this chapter, an allowance is the total difference between the size of a shaft and the hole in the part that fits over it. The resulting fit can be a clearance (loose) fit or interference (tight) fit, or a transitional (somewhere between loose and tight) fit. These three general types of fit are further divided into classes of fit, with each class having a different allowance based on the intended use or function of the parts involved. A brief description of each type fit will be given in the following paragraphs. Any good handbook for machinists has complete charts with detailed information on each class of fit. The majority of equipment repaired in Navy machine shops will have the dimensional sizes and allowances already specified in either the manufacturer's technical manual, NAVSHIPS* Technical Manual, or the appropriate Preventive Maintenance System Maintenance Requirement Card, which is the priority reference on maintenance matters.
CLEARANCE FITS.— Clearance fits, or running and sliding fits as they are often called, provide a varying degree of clearance (looseness) depending on which one of the nine classes is selected. The classes of fit range from class 1 (close sliding fit), which permits a clearance allowance of from +0.0004 to +0.0012 inch on mating parts with a 2.500 inch basic diameter, to class 9 (loose running fit), which permits a clearance allowance of from +0.009 to +0.0205 inch on the same parts. Even for a basic diameter, the small (2.500 inch) clearance allowance from a class 1 minimum to a class 9 maximum differs by +0.0201 inch. As the basic diameter increases, the allowance increases. Although the class of fit may not be specified on a blueprint, the dimensions given for the mating parts are based on the service performed by the parts and the specific conditions under which they operate. Some parts that fall
ing rings (loose removal).
other part.
TRANSITIONAL FITS.— Transitional fits are subdivided into three types known as loca- tional clearances, locational transition and loca- tional interference fits. Each of these three subdivisions contains different classes of fit which provide either a clearance or an interference allowance, depending on the intended use and class. All of the classes of fit in the transitional category are primarily intended for the assembly and disassembly of stationary parts. Stationary in this sense means that the parts will not rotate against each other although they may rotate together as part of a larger assembly. The allowances used as examples in the following descriptions of the various fits represent the sum of the tolerances of the external and internal parts. To achieve maximum standardization and to permit common size reamers and other fixed sized boring tools to be used as much as possible, it is best to use the unilateral tolerance method previously explained and consult one of the class of fit charts in a handbook for machinists.
Locational clearance fits are broken down into 1 1 different classes of fit. The same basic diameter with a class 1 fit ranges from a zero allowance to a clearance allowance of +0.0012 inch, while a class 1 1 fit ranges from a clearance allowance of +0.014 to +0.050 inch. The nearer a part is to a class 1 fit, the more accurately it can be installed without the use of force.
Locational transition fits have six different classes providing either a small amount of clear- ance or an interference allowance, depending on the class of fit selected. The 2.500-inch basic diameter in a class 1 fit ranges from an interference allowance of -0.0003 inch to a clearance allowance of +0.0015 inch while a class 6 fit ranges from an interference allowance of — 0.002 inch to a clearance allowance of +0.0004 inch. The interference allowance fits may require a very light pressure to assemble or disassemble the parts.
Locational interference fits are divided into five different classes of fit, all of which provide an interference allowance of varying amounts. A class 1 fit for a 2.500-inch basic diameter ranges from an interference allowance of -0.0001 to -0.0013 inch, while a class 5 fit ranges from an interference allowance of from -0.0004 to - 0.00023 inch. These classes of fits are used when parts must be located very accurately while main- taining alignment and rigidity. They are not
INTERFERENCE FITS.— There are five classes of fit within the interference type. They are all fits that require force to assemble or disassemble parts. These fits are often called force fits and in certain classes of fit they are referred to as shrink fits. Using the same basic diameter as an example, the class 1 fit ranges from an interference allowance of -0.0006 to -0.0018 inch and a class 5 fit ranges from an interference allowance of - 0.0032 to - 0.0062 inch. The class 5 fit is normally considered to be a shrink fit class because of the large amounts of interference allowance required.
A shrink fit requires that the part with the external diameter be chilled or that the part with the internal diameter be heated. You can chill a part by placing it in a freezer, packing it in dry ice, spraying it with CO2 (do not use a CO2 bottle from a fire station) or by submerging it in liquid nitrogen. All of these methods except the freezer are potentially dangerous, especially the liquid nitrogen, and should NOT be used until all applicable safety precautions have been reviewed and implemented. When a part is chilled, it actually shrinks a certain amount depending on the type of material, design, chilling medium, and length of time of exposure to the chilling medium. You can heat a part by using an oxyacetylene torch, a heat-treating oven, electrical strip heaters or by submerging it in a heated liquid. As with chilling, all applicable safety precautions must be observed. When a part is heated, it expands, allowing easier assembly. All materials expand a different amount per degree of temperature increased. This is called the coefficient of expansion of a metal. Most handbooks for machinists include a chart of the factors and explain their use. It is important that you calculate this information to determine the maximum temperature increase required to expand the part the amount of the shrinkage allowance plus enough clearance to allow assembly. Overheating a part can cause permanent damage and produce so much expansion that assembly becomes difficult.
A general rule of thumb for determining the amount of interference allowance on parts requir- ing a force or shrink fit is to allow approximately 0.0015 inch per inch of diameter of the internally bored part. There are many variables that will prohibit the use of this general rule. The amount
3-31
of interference allowance recommended decreases as the diameter of the part increases. The dimensional difference between the inside and outside diameter (wall thickness) also has an effect on the interference allowance. A part that has large inside and outside diameters and a relatively thin wall thickness will split if installed with an excessive interference allowance. You must consider all of these variables before you select a fit when there are no blueprints or other dimensional references available.
Hydraulic and Arbor Presses
Hydraulic and arbor presses are used in many Navy machine shops. They are used to force broaches through parts, assemble and disassemble equipment with force fitted parts, and many other shop projects.
Arbor presses are usually bench mounted with a gear and gear rack arrangement. They are used for light pressing jobs, such as pressing arbors or mandrels into a part for machining or forcing a small broach through a part.
Hydraulic presses can be either vertical or horizontal, although the vertical design is probably more common and versatile. The pressure that a hydraulic press can generate ranges from about 10 to 100 tons in most of the Navy machine shops. The pressure can be exerted by either a manually operated pump or an electro- hydraulic pump.
Regardless of the type of press equipment you use, be sure to operate it correctly. The only way you can determine the amount of pressure a hydraulic press exerts is by watching the pressure gauge. A part being pressed can reach the break- ing point without any visible indication that too much pressure is being applied. When using the press, you must consider the interference allowance between mating parts; corrosion and marred edges; and overlooked fastening devices, such as pins, setscrews, and retainer rings.
To prevent damage to the work, observe the following precautions whenever you use a hydraulic press:
• Ensure that the work is adequately supported.
• Place the ram in contact with the work by hand, so that the work is positioned accurately in alignment with the ram.
• Use a piece of brass or other material (preferably slightly softer than the workpiece) between the face of the ram and the work to prevent mutilation of the "surface of the workpiece.
• Watch the pressure gauge. You cannot determine the pressure exerted by "feel." If you begin to apply excessive pressure, release the pressure and double check the work to find the cause.
• When pressing parts together, use a lubricant between the mating parts to prevent seizing.
Information concerning the pressure required to force fit two mating parts together is available in most handbooks for machinists. The distance the parts must be pressed directly affects the required pressure, and increased interference allowance requires greater pressure. As a guideline for force-fitting a cylindrical shaft, the maximum pressure, in tons, should not exceed 7 to 10 times the shaft's diameter in inches.
Oxyacetylene Equipment
As a Machinery Repairman, you may have to use an oxyacetylene torch to heat parts to expand them enough to permit assembly or disassembly. Do this with great care, and only with proper supervision. The operation of the oxyacetylene torch, as used in heating parts only, is explained in this chapter along with safety precautions which you must observe when you use the torch and related equipment.
Oxyacetylene equipment consists of a cylinder of acetylene, a cylinder of oxygen, two regulators, two lengths of hose with fittings, a welding torch with tips, and either a cutting attachment or a separate cutting torch. Accessories include a spark lighter to light the torch; an apparatus wrench to fit the various connections, regulators, cylinders, and torches; goggles with filter lenses for eye protection; and gloves for protection of the hands. Flame-resistant clothing is worn when necessary.
Acetylene (chemical formula C2H2) is a fuel gas made up of carbon and hydrogen. When burned with oxygen, acetylene produces a very hot flame having a temperature between 5700 ° and 6300 °F. Acetylene gas is colorless, but has a distinct, easily recognized odor. The acetylene used on board ship is usually taken from compressed gas cylinders.
3-32
burn by itself, but it will support combustion when combined with other gases. You must be extremely careful to ensure that compressed oxygen does not become contaminated with hydrogen or hydrocarbon gases or liquids, unless the oxygen is controlled by such means as the mixing chamber of a torch. A highly explosive mixture will be formed if uncontrolled compressed oxygen becomes contaminated. Oxygen should NEVER come in contact with oil or grease.
The gas pressure in a cylinder must be reduced to a suitable working pressure before it can be used. This pressure reduction is accomplished by an LC REGULATOR or reducing valve. Regulators that control the flow of gas from the cylinder are either the single-stage or the double- stage type. Single-stage regulators reduce the pressure of the gas in one step; two-stage regulators do the same job in two steps, or stages. Less adjustment is generally necessary when two- stage regulators are used.
The hose connected between the torch and the regulators is strong, nonporous, and sufficiently flexible and light to make torch movements easy. The hose is made to withstand high, internal pressures, and the rubber from which it is made is specially treated to remove sulfur to avoid the danger of spontaneous combustion. Welding hose is available in various sizes, depending upon the size of work for which it is intended. Hose used for light work has a 3/16- or 1/4-inch inside diameter, and contains one or two plies of fabric. For heavy duty welding and handcutting operations, hose with an inside diameter of 1/4 or 5/16 inch and three to five plies of fabric is used. Single hose comes in lengths of 12 1/2 feet to 25 feet. Some manufacturers make a double hose which conforms to the same general specifications. The hoses used for acetylene and oxygen have the same grade but differ in color and have different types of threads on the hose fittings. The oxygen hose is GREEN and the acetylene hose is RED. The oxygen hose has right- hand threads and the acetylene hose has left-hand threads for added protection against switching the hoses during connection.
The oxyacetylene torch is used to mix oxygen and acetylene gas in the proper proportions and to control the volume of these gases burned at the torch tip. Torches have two needle valves, one for adjusting the flow of oxygen and the other for adjusting the flow of acetylene. In addition, they have a handle (body), two tubes (one for oxygen
which dissipates heat (less than 60% copper) and are available in different sizes to handle a wide range of plate thicknesses.
Torch tips and mixers made by different manufacturers differ in design. Some makes of torches have an individual mixing head or mixer for each size of tip. Other makes have only one mixer for several tip sizes. Tips come in various types. Some are one-piece, hard copper tips. Others are two-piece tips that include an extension tube to make connection between the tip and the mixing head. When used with an extension tube, removable tips are made of hard copper, brass, or bronze. Tip sizes are designated by numbers, and each manufacturer has its own arrangement for classifying them. Tips have different hole diameters.
No matter what type or size tip you select, you must keep the tip clean. Quite often the orifice becomes clogged. When this happens, the flame will not burn properly. Inspect the tip before you use it. If the passage is obstructed, you can clear it with wire tip cleaners of the proper diameter, or with soft copper wire. Do not clean tips with machinist's drills or other sharp instruments.
Each different type of torch and tip size requires a specific working pressure to operate properly and safely. These pressures are set by adjusting the regular gauges to the setting prescribed by charts provided by the manufac- turer.
PROCEDURE FOR SETTING UP OX- YACETYLENE EQUIPMENT.— Take the
following steps in setting up oxyacetylene equipment:
1. Secure the cylinders so they cannot be upset. Remove the protective caps.
2. Crack (open) the cylinder valves slightly to blow out any dirt that may be in the valves. Close the valves and wipe the connections with a clean cloth.
3. Connect the acetylene pressure regulator to the acetylene cylinder and the oxygen pressure regulator to the oxygen cylinder. Using the appropriate wrench provided with the equipment tighten the connecting nuts.
4. Connect the red hose to the acetylene regulator and the green hose to the oxygen regulator. Tighten the connecting nuts enough to prevent leakage.
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5. Turn the regulator screws out until you feel little or no resistance then open the cylinder valves slowly. Then open the acetylene valve 1/4 to 1/2 turn. This will allow an adequate flow of acetylene and the valve can be turned off quickly in an emergency. (NEVER open the acetylene cylinder valve more than 11/2 turns.) Open the oxygen cylinder valve all the way to eliminate leakage around the stem. (Oxygen valves are double seated or have diaphragms to prevent leakage when open.) Read the high-pressure gauge to check the pressure of each cylinder.
6. Blow out the oxygen hose by turning the regulator screw in and then back out again. If you need to blow out the acetylene hose, do it ONLY in a well-ventilated place that is free from sparks, flames, or other possible sources of ignition.
7. Connect the hoses to the torch. Connect the red acetylene hose to the connection gland that has the needle valve marked AC or ACET. Connect the green oxygen hose to the connection gland that has the needle valve marked OX. Test all hose connections for leaks by turning both regulator screws IN, while the needle valves are closed. Then turn the regulator screws OUT, and drain the hose by opening the needle valves.
8. Adjust the tip— Screw the tip into the mixing head and screw the mixing head onto the torch body. Tighten the mixing head/tip assembly by hand and adjust the tip to the proper angle. Secure this adjustment by tightening the assembly with the wrench provided with the torch.
9. Adjust the working pressures — Adjust the acetylene pressure by turning the acetylene gauge screw to the right. Adjust the acetylene regulator to the required working pressure for the particular tip size. (Acetylene pressure should NEVER exceed 15 psig.)
10. Light and adjust the flame — Open the acetylene needle valve on the torch and light the acetylene with a spark lighter. Keep your hand out of the way. Adjust the acetylene valve until the flame just leaves the tip face. Open and adjust the oxygen valve until you get the proper neutral flame. Notice that the pure acetylene flame which just leaves the tip face is drawn back to the tip face when the oxygen is turned on.
PROCEDURE FOR ADJUSTING THE FLAME. — A pure acetylene flame is long and bushy and has a yellowish color. It is burned by the oxygen in the air, which is not sufficient to burn the acetylene completely; therefore, the flame is smoky, producing a soot of fine, unburned carbon. The pure acetylene flame is
unsuitable lor use. When the oxygen valve is opened, the mixed gases burn in contact with the tip face. The flame changes to a bluish- white color and forms a bright inner cone surrounded by an outer flame envelope. The inner cone develops the high temperature required.
The type of flame commonly used for heating parts is a neutral flame. The neutral flame is produced by burning one part of oxygen with one part of acetylene. The bottled oxygen, together with the oxygen in the air, produces complete combustion of the acetylene. The luminous white cone is well-defined and there is no greenish tinge of acetylene at its tip, nor is there an excess of oxygen. A neutral flame is obtained by gradually opening the oxygen valve to shorten the acetylene flame until a clearly defined inner luminous cone is visible. This is the correct flame to use for many metals. The temperature at the tip of the inner cone is about 5900 °F, while at the extreme end of the outer cone it is only about 2300 °F. This gives you a chance to exercise some temperature control by moving the torch closer to or farther from the work.
EXTINGUISHING THE OXYACETYLENE FLAME.— To extinguish the oxy acetylene flame and to secure equipment after completing a job, or when work is to be interrupted temporarily, you should take the following steps:
1. Close the acetylene needle valve first; this extinguishes the flame and prevents flashback. (Flashback is discussed later.) Then close the oxygen needle valve.
2. Close both the oxygen and acetylene cylinder valves. Leave the oxygen and acetylene regulators open temporarily.
3. Open the acetylene needle valve on the torch and allow gas in the hose to escape for 5 to 15 seconds. Do NOT allow gas to escape into a small or closed compartment. Close the acetylene needle valve.
4. Open the oxygen needle valve on the torch. Allow gas in the hose to escape for 5 to 15 seconds. Close the valve.
5. Close both oxygen and acetylene cylinder regulators by backing out the adjusting screws until they are loose.
Follow the above procedure whenever your work will be interrupted for an indefinite period. If your work is to stop for only a few minutes, securing the cylinder valves and draining the hoses is not necessary. However, for any indefinite work
in areas other than the shop, it is a good idea to remove the pressure regulators and the torch from the system and to double check the cylinder valves to make sure that they are closed securely.
SAFETY: OXYACETYLENE EQUIPMENT
When you are heating with oxyacetylene equipment, you must observe certain safety precautions to protect personnel and equipment from injury by fire or explosion. The precautions which follow apply specifically to oxyacetylene work.
• Use only approved apparatus that has been examined and tested for safety.
• When you use cylinders, keep them far enough away from the actual heating area so they will not be reached by the flame or sparks from the object being heated.
• NEVER interchange hoses, regulators, or other apparatus intended for oxygen with those intended for acetylene.
• Keep valves closed on empty cylinders.
• Do NOT stand in front of cylinder valves while opening them.
• When a special wrench is required to open a cylinder valve, leave the wrench in position on the valve stem while you use the cylinder so the valve can be closed rapidly in an emergency.
• Always open cylinder valves slowly. (Do NOT open the acetylene cylinder valve more than 1 1/2 turns.)
• Close the cylinder valves before moving the cylinders.
• NEVER attempt to force unmatching or crossed threads on valve outlets, hose couplings, or torch valve inlets. The threads on oxygen regulator outlets, hose couplings, and torch valve inlets are right-handed; for acetylene, these threads are left-handed. The threads on acetylene cylinder valve outlets are right-handed, but have a pitch that is different from the pitch of the threads on the oxygen cylinder valve outlets. If the threads do not match, the connections are mixed.
involved. This information should be taken from tables or worksheets supplied with the equipment.
• Do NOT allow acetylene and oxygen to ac- cumulate in confined spaces. Such a mixture is highly explosive.
• Keep a clear space between the cylinder and the work so the cylinder valves may be reached quickly and easily if necessary.
• When lighting the torch, use friction lighters, stationary pilot flames, or some other suitable source of ignition. The use of matches may cause serious hand burns. Do NOT light a torch from hot metal. When lighting the torch, open the acetylene valve first and ignite the gas with the oxygen valve closed. Do NOT allow unburned acetylene to escape into a small or closed compartment.
• When extinguishing the torch, close the acetylene valve first and then close the oxygen valve.
• Do NOT use lubricants that contain oil or grease on oxyacetylene equipment. OIL OR GREASE IN THE PRESENCE OF OXY- GEN UNDER PRESSURE WILL IGNITE VIOLENTLY. Consequently, oxygen must not be permitted to come in contact with these materials in any way. Do NOT handle cylinders, valves, regulators, hose, or any other apparatus which uses oxygen under pressure with oily hands or gloves. Do NOT permit a jet of oxygen to strike an oily surface or oily clothes. NOTE: A suitable lubricant for oxyacetylene equipment is glycerin.
• NEVER use acetylene from cylinders without reducing the pressure through a suitable pressure reducing regulator. Avoid acetylene working pressures in excess of 15 pounds per square inch. Oxygen cylinder pressure must likewise be reduced to a suitable low working pressure; high pressure may burst the hose.
• Stow all cylinders carefully according to prescribed procedures. Store cylinders in dry, well- ventilated, well-protected places away from heat and combustible materials. Do NOT stow oxygen cylinders in the same compartment with acetylene cylinders. Stow all cylinders in an upright position. If they are not stowed in an upright position, do not use them until they have been allowed to stand upright for at least 2 hours.
3-35
cylinder, or on any flammable materials. Be sure a fire watch is posted as required to prevent accidental fires.
Be sure you and anyone nearby wear flame- proof protective clothing and shaded goggles to prevent serious burns to the skin or the eyes. A number 5 or 6 shaded lens should be sufficient for your heating operations.
These precautions are by no means all the safety precautions that pertain to oxyacetylene equipment, and they only supplement those specified by the manufacturer. Always read the manufacturer's manual and adhere to all pre- cautions and procedures for the specific equip- ment you are going to be using.
Flashback and Backfire
A backfire and a flashback are two common problems encountered in using an oxyacetylene torch.
Unless the system is thoroughly purged of air and all connections in the system are tight before the torch is ignited, the flame is likely to burn in- side the torch instead of outside the tip. The difference between the two terms backfire and flashback is this: in a backfire, there is a momentary burning back of the flame into the torch tip; in a flashback, the flame burns in or beyond the torch mixing chamber. A backfire is characteristized by a loud snap or pop as the flame goes out. A flashback is usually accompanied by a hissing or squealing sound. At the same time, the flame at the tip becomes smoky and sharp- pointed. When a flashback occurs, immediately shut off the torch oxygen valve, then close the acetylene valve.
A flashback indicates that something is radically wrong either with the torch or with the manner of handling it. A backfire is less serious. Usually the flame can be relighted without difficulty. If backfiring continues whenever the torch is relighted, check for these causes; overheated tip, gas working pressures greater than that recommended for the tip size being used, loose tip, or dirt on the torch tip seat. These same difficulties may be the cause of a flashback, except that the difficulty is present to a greater degree. For example, the torch head may be distorted or cracked.
In most instances, backfires and flash- backs result from carelessness. To avoid these
closed) when the equipment is stowed, (3) the oxygen and acetylene working pressures used are those recommended for the torch, and (4) you have purged the system of air before using it. Purging the system of air is especially necessary when the hose and torch have been newly connected or when a new cylinder is put into the system.
PURGING THE OXYACETYLENE TORCH.—
1 . Close the torch valves tightly, then slowly open the cylinder valves.
2. Open the acetylene regulator slightly.
3. Open the torch acetylene valve and allow acetylene to escape for 5 to 15 seconds, depending on the length of the hose.
4. Close the acetylene valve.
5. Repeat the procedure on the oxygen side of the system.
After purging air from the system, light the torch as described previously.
FASTENING DEVICES
Parts of machinery and equipment are held together by several types of fastening devices. The fastening devices commonly used by the Machinery Repairman are classified into three general groups: threads, keys, and pins.
The selection of the correct fastener (specified in blueprints, list of material blocks, and technical manuals) and the use of an approved installation method are important factors in the efficiency and reliability of a piece of equipment. Improper use of fasteners will lead to equipment failures and possible personnel injuries.
Threaded Fastening Devices
Bolts, studs, nuts, capscrews, machine screws and setscrews are all threaded devices used to clamp or secure mating parts together. Each of the different types has a specific range of applica- tions and is available in various sizes, designs and material specifications. The most common sizes evolve from the established diameters, threads per inch, and classes of fit described in the Unified (UNC, UNF) and the American National (NC, NF) thread systems explained in chapter 9. The
3-36
j. uii£,v \jt. £,viivi u.j. cippjuvcii..ivji.io iv^i any givtii
fastener. However, some equipment requires such specialized fasteners that the fasteners can only be used for that specific purpose. The material specification for a certain application of a fastener is based on the function of the mating parts, stresses, and temperatures applied to the fasteners and on the elements to which the equip- ment is exposed, such as steam, saltwater and oil. Table 3-3 is a general guide for material usage and the different identifying markings found on fasteners.
BOLTS.— A bolt is an externally threaded fastener, with a threaded diameter of 1/4 inch or larger, and either a squarely or hexagonally shaped head. Bolts are designed to be inserted into holes slightly larger than their diameter. A nut is attached to the threaded end to draw the mating parts together. As a general rule, the width of the
thread ranges from 2 times the thread diameter plus 1/4 inch to a point just below the head, depending on the intended use. The length of the bolt is measured from the under side of the head to the tip of the threaded portion. It is best to use a bolt that has an unthreaded length slightly less than the combined thickness of the parts being mated. The overall length should allow a minimum of 1 full thread and a maximum of 10 threads (space permitting) to protrude above the nut after the assembly is completely torqued down. The class of fit normally found on the threads of bolts and the nuts used with them is class 2A for the bolt and class 2B for the nut. This fit permits an allowance so that the bolt and nut can be assembled without seizing or galling. Detailed information on the different classes of fit for threads is covered later in this manual.
Table 3-3. — Specifications and Uses of Fasteners
|
MATERIAL |
MATERIAL SPECS. |
GRADE |
CONDITION |
MARKING ON FASTENER |
INTENDED USE |
|
CARBON STEEL |
SAE 10XX SERIES STEEL WITH A MAX IMUM OF 0.55% |
5 |
HEAT TREATED |
3 EQUALLY SPACED RADIAL LINES |
GENERAL USE |
|
CARBON STEEL |
CARBON |
8 |
HEAT TREATED |
6 EQUALLY SPACED RADIAL LINES |
GENERAL USE |
|
ALLOY STEEL |
SAE 4140 TO SAE 4145 |
B7 |
HEAT TREATED |
B7 |
FOR USE UP TO 775°F WITH GRADE 2H AND GRADE 4 NUTS |
|
ALLOY STEEL |
ASTM A 193 |
B16 |
HEAT TREATED |
B16 |
FOR USE UP TO 1000°F WITH GRADE 4 NUT |
|
CORROSION RESISTANT STEEL |
FED. STD. 66 |
303 |
ANNEALED |
303 |
FOR USE WHERE LOW MAGNETIC AND CORROSION RESISTANT PROPERTIES ARE REQUIRED |
|
CORROSION RESISTANT STEEL |
FED. STD. 66 |
41 OT |
HEAT TREATED |
410 |
FOR USE WHERE LOW MAGNETIC AND CORROSION RESISTANT PROPERTIES ARE REQUIRED |
|
NAVAL BRASS |
QQ-B-637 |
482 |
— |
482 |
FOR CONNECTING NON-FERROUS MATERIALS IN CONTACT WITH SALT WATER |
|
SILICON BRONZE |
QQ-C-591 |
651 |
— |
651 |
FOR CONNECTING NON-FERROUS MATERIALS IN CONTACT WITH SALT WATER |
|
NICKLE COPPER |
QQ-N-281 CL. A&B |
400 |
400 |
FOR CONNECTING FERROUS AND NON-FERROUS MATERIALS (EXCEPT ALUMINUM) IN CONTACT WITH SALT WATER |
|
|
NICKLE COPPER ALUMINUM |
QQ-N-286 CL.A |
500 |
— |
500 |
FOR CONNECTING FERROUS AND NON-FERROUS MATERIALS (EXCEPT ALUMINUM) IN CONTACT WITH SALTWATER |
|
CARBON STEEL |
SAE 10XX SERIES STEEL WITH A MAX. OF 0.55% CARBON |
2H |
HEAT TREATED |
2H (NUTS ONLY) |
FOR USE UP TO 775°F WITH GRADE B7 STUD OR BOLT |
|
ALLOY STEEL |
SAE 4140 to SAE 4145 |
4 |
HEAT TREATED |
4 (NUTS ONLY) |
FOR USE UP TO 1000°F WITH GRADE B16 AND B7 STUD OR BOLT |
3-37
fastener with threads on both ends. It can either be inserted through a clearance hole and secured by a nut on each end, or it can be used in an assembly where one part has a tapped hole and the second part has a clearance hole. In the latter case, the stud is screwed into the tapped hole and a nut is screwed onto the other end of the stud. One type of stud is continuously threaded, with threads beginning at one end and running the entire length of the stud. Another type of stud has threads beginning at each end and an un- threaded portion in the center of the stud. The unthreaded portion may have the same diameter as the major diameter of the threads, or it may be recessed to provide clearance. A continuously threaded stud generally has a class 2A or 3A fit to allow relative ease in assembly. A stud with the center portion unthreaded may have a different class of fit on each end. One end will have a class 2A or 3A fit. This is the end on which the nut is screwed. The end of the stud that screws into the tapped hole will have an interference fit that will require a torque wrench to install it. The interference fit is a class 5 fit and is divided into several subdivisions to provide the correct fit for different materials and lengths of engagement. A stud of this type is screwed into the tapped hole the maximum distance possible without jamming either the end of the stud against the bottom of the hole or the shoulder of the unthreaded part of the stud against the top of the tapped hole. A small amount of lubricant approved for use in the temperature range in which the equipment is exposed should be applied to the threads. You will find the correct tolerances and torque required for each application in charts in most handbooks for machinists.
NUTS. — A nut is an internally threaded fastener with the same size threads as the externally threaded part to which it will be attached. Nuts come in either square or a hexagon shapes and have standard widths and thicknesses based on the basic thread size. Any application of threaded fasteners that are subjected to working conditions which could cause the nut to loosen through heat or vibration usually has some method of locking the mating parts securely. Several methods are available to you. You may use different styles of lock washers, deform the area around the threads by staking or peening with a center punch, install setscrews, or use locknuts.
Locknuts in common use are of two types. One type applies pressure to the bolt or stud
and is used when the nut must be removed frequently. Included in this type are jam nuts, a thin