INTRODUCTION TO TOOL ENGINEERING By Edward M* Pouch A Thesis Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in fulfillment of the requirements for the degree of PROFESSIONAL DEGREE IN MECHANICAL ENGINEERING Department of Engineering 1953 ProQuest Number: 10008304 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10008304 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This w ork is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346 TABLE OP CONTENTS CHAPTER I. II. PAGE INTRODUCTORY CHAPTER Objective of thesis 1 Definition of tool engineering 2 Background of tool engineering 3 Place in organization 4 Responsibilities and objectives 5 Tooling up for production 8 TOOL DESIGN The tool designer 12 Jigs and fixtures 15 Difference between jigs and fixtures 16 Elements of jig and fixture design 18 Objective of good design from the standpoint of motion economy 43 Eliminate barriers 44 Provide sufficient chip clearance 45 Provide fixture relief 46 Provide quick clamping 46 Provide mechanical assistance 47 Provide multiple station fixtures 48 Provide for minimum material and maintenance cost 48 CHAPTER PAGE Gages III. Gages and gaging 50 Manufacturing gages 52 Inspection gages 64 Reference gages 65 PRODUCTION MACHINERY Introduction to chapter 66 Selection of proper machine 69 Type of manufacturing 69 Volume of production 71 Manufacturing equipment available 71 Required quality of finish 72 Drilling machines 74 Turning machines 84 Milling machines 97 Grinding machines i05 Planers, shapers and blotters 120 Broac hing machine s IV, 125 Honing, lapping andsuperfinishing 127 Special purpose machines 132 SUMMARY 137 BIBLIOGRAPHY 141 LIST OP TABLES PAGE TABLE I. Finishes Obtainable by Various Machining Methods 7^ LIST OP FIGURES FIGURES 1. PAGE Typical Jig Bushing, Liners, Lock Screws and Clamps 21 Typical Jig Bushing, Liner, Lock Screw and Clamp Installation 22 3* Examples of V Locators 25 4* Examples of Relieved Locators 25 5* Two Simple Fixed or Non-adjustable Stops 26 6. Adjustable Stops that can lock into 2. Position 26 7* Fixed Stop with Two Point Bearing 26 8. Rest Buttons or Jig Feet 26 9. Milling Machine Vise and Typical Jaws 28 10* Four Standard Types of Jig and Fixture Clamps 11# Clamping Principles 12* Drilling and Removing Slip Bushing for an Unguided Secondary Operation 13. 14. 15. 31 32 35 Using Two Sizes of Slip Bushings for Drill­ ing and Counterboring with Flat Pointed Drill 35 Using Two Slip Bushings to Drill and Counter­ sink with the end of Bushing Guided Drill 35 An Example of the Use of a Flipper Bushing to Facilitate the Secondary Operation 36 16. Placement of the Bushing 38 17. Examples of Corner Relief for Chip Control 39 18. Classification of Measuring Instruments 53 19. Various Types of Plug Gages 55 PAGE Two Types of Adjustable Snap Gages 58 Non-adjustable Snap Gages 59 Various Types of Plush Pin Gages 61 Thread Gages 65 A Single Spindle Power Peed Drill Press with a Typical Multiple Head and Indexing Jig often used with this Machine 80 A Multiple Spindle Power Peed Drill Press 81 A Modern Production Type Engine Lathe 86 A Typical Turret Lathe 91 A Multiple Spindle Automatic Chucking Machine 91 A Vertical Turret Lathe 95 A Multiple Spindle Vertical Turret Lathe 95 Knee and Column Type Plain Horizontal Milling Machine 101 Knee and Column Type Plain Vertical Milling Machine 101 A Thread Milling Machine 106 Showing Relation of Cutter and Work in the Thread Mill 106 A Cylindrical Grinder 109 A Modern Production Type Center less Grinder 113 A Typical Internal Grinder 117 External Thread Grinding Machine 120 Internal Thread Grinding Machine 120 Continuous Broaching Machine, Broach Holder and Workholding Fixture 126 Special Drilling, Countersinking and Tapping Machine 133 CHAPTER I I. OBJECTIVE OF THESIS The objective of this thesis is primarily to introduce tool engineering and its work in the modern manufacturing industry; secondly, to discuss the purpose, function, and some of the ”kncw-hcwM of this technical profession. From many definitions, the tool engineering group would seem to have two major objectives: 1. To devise means and equipment to achieve and, main­ tain a desired level of quality in a manufactured product 2. To accomplish the results in the most economical manner. The discussion of tool engineering, its work and the manner in which it accomplishes its major objectives will be interesting to both the technical student and the practicing engineer. To the technical student it will offer a background of industrial information that will give a better understand­ ing of modern industry. To the practicing engineer it may present a new approach to some old problems. II. DEFINITION OF TOOL ENGINEERING The definitions set forth for tool engineering are many and varied but there are valid reasons for the lack of agreement on the inclusion of certain activities within the classification. Tool engineering is a rapidly expand­ ing field and in each organization the department has been set up to suit the size of the organization, the product, production requirements, and in many cases has been influenced by the available manpower. The following definition by a prominent tool engineer is quite authoritative: ”The Tool Engineer is a specialist in the design and application of tools, jigs, fixtures, and other manufacturing equipment, which are important factors in determining the end cost of the product. In other definitions will be found the inclusion of the words: analysis, planning, construction, application, processing and estimating. Thus, along with the development of large mass production industries, the tool engineering classification has acquired many ramifications. In general, the term has been recognized as meaning the design and selection of the necessary tools and machinery for the economical production of a given quantity of parts or assemblies. 1 C. E. J. Brickner, "The Tool Engineers Place in the Industry”, Tool Engineer, July 19^6 P* 57* III. TOOL ENGINEERING Background of tool engineering. In modern industry the experience and knowledge of tools, machines, and processes, together with the "know-how" of low cost production, is found a group whose function within an organization was not clearly defined until recent years. The work performed in this field has existed in industry for many years, but the complexity of modern production has brought about the grouping of the various kinds of work into a common functioning department. This group is designated by different companies as manufacturing engineering, pro­ duction engineering, process engineering, and tool engineer­ ing. Many other designations are used but the foregoing are the most common. Of these the terms "tool engineering" is the most nearly universal. Although the tool engineering group is a comparative newcomer in the industrial world, this does not mean that under such conditions that tool activities did not exist. The tooling functions were assumed by the shop supervisors, foremen or mechanics. small shops. This practice still exists in many 4 With the coming of mass production, standardization and interchangeability in manufacturing, the tool engineering took Its place in the industrial field. The continuing expansion and enlargoent in the size of industrial enter­ prises brought forth more complex and extensive problems, thus presenting opportunities for a more specialized and concentrated study of them. This entrance into the manu­ facturing field of many technically trained engineers brought the influence and viewpoint of specialist. This brought about a new analytical and scientific approach to attacking manufacturing problems. Among concepts introduced was that all manufacturing personnel or persons engaged directly in production should be relieved of all planning, preparation, and calculations and those functions should be assigned to specialist capable of applying the utmost of skill and knowledge• Place in organization. Upon examination of the organiza­ tion chart of many leading manufacturing companies, it would be noticed that there are as many variations as there are establishments, and that all the charts differ somewhat as to the key positions. This is as would be expected for each company has grown through the manufacture of a wide and varied range of products, and each company has aaly those executives and departments necessary to produce the finished product. In 5 one company the tool engineering department perhaps would be under the jurisdiction of the plant manager, in another under the plant superintendent, in another it might be under the guidance of a chief engineer or general engineering depart­ ment • The work of this department falls between that of product engineering and the production departments. The term "tool engineer” has been applied to the head of the department in the sense that he symbolizes its character. In some plants he may be known as the master mechanic, chief tool engineer or the chief tool designer. The tool engineering division may be divided up into various groups designated by their particular specialties, such as, process engineers, tool engineers, or estimators. Any of the engineering employes specializing in any department of the tool engineering division can be termed "tool engineers". Responsibilities and objectives. The tool engineering division is committed to the ideal of the most economical production possible under existing conditions of available equipment, financial considerations and quality requirements. These things are their responsibilities either directly or indirectly. Always foremost is the desire for greater economy. selling cost depends on many factors. The Some of these, such as the cost of raw materials, interest rates, marketing expenses, patents, taxes and tariff rates, do not involve tool engineering 6 directly. In others, such as the correct design of the product, the choice of raw materials, the selection of manufacturing methods, tool engineering shares the responsibility with other members of the organization. Actual manufacturing costs^ hcwever, are the direct concern of tool engineering* This group is always endeavoring to lower the factory cost on every article fabricated. This is accomplished by the design of labor saving tools, machines and devices to fill the need where the usual standard tools cannot be used economically to produce quantities of the product to be made. Tool engineering is charged with the responsibility of cooperating with the product engineers so that the design will be economically producible as well as functional. Tool engineering SBlects the best manufacturing methods, Indicates the proper equipment to be used, establishes the proper sequence of manufacture, designs, estimates tool costs, pro­ cures the required machines and tools, and supervises their installation, and generally consolidates these items into a smooth working plan of production. No matter what the product Is, or where it Is going to be used, the objectives of executives, engineers, and salesmen and the other members of a manufacturing concern Is to produce a product of the highest quality at the lcwest possible selling price. Through the design of efficient tools and the selection of proper machines, tool engineering is able 7 to achieve reduction of manufacturing cost* accuracy of parts, and the elimination of the need for operational skill. An increase in the accuracy of the part means a uniform product of higher quality. This is an important factor in sales and future orders. The other two items are very closely related. If the need for operational skill is reduced or eliminated, the labor base is broadened, which is to say that the range of intel­ ligence of the men required to run the plant is broadened. The man of high operational skill can be used on an operation requiring his skill, while a semi-skilled worker can do a job to suit his ability. Even those workers possessing a minimum of intelligence can be employed. for more workers. This means more employment Thus, by the transfer of the skill from the worker to the tool, the high degree of operational skill once demanded of a worker is no longer needed; therefore, one of the two main manufacturing costs - direct labor - has been reduced. Tool engineering is also aware of the other factor of manufacturing cost; that is, Investment cost on the tools and machines. each other. Both must be as low as possible and both influence It Is always possible to lower labor cost by investing in tools. Likewise a savings in investment cost generally means higher labor cost. In all cases a compromise must be made and as much ingenuity and skill as possible 8 should he used to Insure the best tools for the least expenditure» The cost of the product Is further reduced by planning the flow of production according to a fixed time schedule, Increasing the rate of production to the maximum economical output of the machine and to reduce waste time and material# These are some of the more Important responsibilities and objectives of the tool engineering division# Tooling u p for production# There are many different types of "tooling u p 1’ methods and we cannot study all of them thoroughly here# Only a general view of the part tool engineering plays in modern industry can be presented# Tool­ ing programs are often undertaken with a view to provide new tools for a product that has been steadily increasing in sales for some time or for a new product# In addition, tool designers are often called upon to redesign tools that are not quite satisfactory in service, or to improve tools where operators, foremen and others offer worthwhile suggestions# Of course, the biggest "tooling up" program of all Is the preparation to produce a part or assembly never before manufactured* After the sales department has made contact with the customer concerning a new product to be manufactured, all of the available information Is passed on to the product engineer# The part or assemblies will be designed by the product engineers# They will be primarily responsible for the proper functioning 9 of the part or assembly* They should, however, have given some consideration to economical manufacture, but since they are not connected with detailed shop processes as the tool engineer Is, they may have overlooked a few factors* Consequently, tool engineering first considers the possibility of design changes in the part for easier production* Under no circumstances are they allowed to make any changes them­ selves, but suggest the necessary changes to the product engineer* When the design of the product is released by the engineering department, blueprints of all of the parts are sent to tool engineering division* The tool engineers and factory executives then begin the study of the manufacturing program* The tool engineer must be familiar with the equip­ ment and the resources of the factory. They must learn the approximate number of units to be made to be able to estimate the amount of money required for investment in new tools* The general manager has the final decision as to the expendi­ ture* Sometimes the general manager requests an estimate of the proposed cost of new tools which he approves or modifies ; or he m a y tell the tool engineer hew much will be allowed for the tooling program. After careful consideration has been given to the items, tool engineering starts to break down the manufacturing process into individual operations. At this time tool engineering 10 begins the selection of the proper production machinery and starts to design the necessary jigs, fixtures, gages, etc. In the foregoing pages tool engineering has been intro­ duced showing its history and background. In another section tool engineering*s place in the Industrial organization was discussed, and also the division of the tool department into various specialist groups. Some of the tool engineer's responsibilities both direct and indirect were considered, and also his major objectives in connection with his work. In a section on ”tooling u p ” for production, it was shewn how the tooling process proceeds from the sales department down through the design to the tool engineer. In the following chapters will be discussed the two major problems of tool engineering; that is, tool design and production machinery. In the chapter on tool design, the all-important work of the tool engineering department is taken up In some detail. The design of jigs, fixtures, and gages is one of the more important parts of the engineer's work. In line with the design work, the objectives of good fixture design from the standpoint of motion economy will be considered. In the will become last chapter on production machinery the reader acquainted with production machinery and Its 11 purpose* This will Include the reasoning involved in the selection of the proper machine. Special emphasis has been placed on the ultimate pro­ duction of manufactured goods by the most economical means and the necessary procedures by which that end is attained. The text of the thesis does not cover all the ramifications of tool engineering, but it does describe major points supplemented by illustrations and tables, the problems encountered and the need for a knowledge of jigs, fixtures, gages and machines by the tool engineer. CHAPTER II TOOL DESIGN The essential purpose of the tool to furnish designs and drawings of the design department is necessary jigs, fixtures, dies, tool layouts and gages for the complete tooling of any desired part. The design of practical jigs, fixtures and gages constitutes the greater part of the tool designer's work. This chapter will he confined to the basic principles of design of these items and the objective of good jig and fixture design from the standpoint of motion economy. I. THE TOOL DESIGNER The first work the young designer, or detailer as he will be known, is called upon to do is usually that of making detail drawings of the individual parts of a jig, fixture or gage, the assembly or general plans of developed by his superiors. which have been As the detailer increases his experience and knowledge of the basic principles of jig, fixture, and gage design he will be advanced through the steps of senior detailer, junior designer to senior designer. and more he will be allowed to develop his own ideas. More For the designer to efficiently design all the various jigs and 13 fixtures used in a modern manufacturing establishment, he must be virtually a storehouse of ideas* While the basic principles of jig and fixture design are not too many in number and comparatively simple, the true worth of the designer depends upon his ability to apply basic principles in an original and Ingenious manner. The fact that the tool designer spends a great deal of time at that drafting board often leads to the erroneous impression that designing is a form of drafting. At first glance this impression may seem justified, but drafting actually is only indirectly related to tool design. The relationship of drafting to tool design is similar to that of writing to thinking. Drafting is a descriptive method of expressing ideas beyond the limitations of the written or spoken word. There is every reason to believe that the real work of the designer may be completed while the proposed tool is still in the form of an idea. When the designer starts to draw he must have already visualised the tool he wishes to put on paper. He has to lay out the tool, often changing minor details and proportions, but this is only a recording process for his ideas# In other words, the work of the designer is largely mental and is essentially a process of visualization.2 2j. I. Karash, Analysis of DriDrJig Design, New Yorks McGraw-Hill Book Company, 1944, preface. 14 As the discussion continues the reader will realize more and more the multiplicity of items of knowledge and ideas the designer must have at his command. While every tool designer is confronted by different problems, there are certain fundamental principles which can be modified to meet the existing conditions and apply in most cases. While all the devices used by the designer will not be exhausted by any means, it will be endeavored to shew some of the general principles which are helpful in design work. II. JIGS AND FIXTURES Jigs and fixtures have become such a necessary part of modern manufacturing in a large percentage of the work done that an understanding of the principles involved is a neces­ sity in every shop. The two most important reasons for jigs and fixtures are reduced cost and interchangeability of manufactured parts. The use of jigs and fixtures is primarily to reduce the labor cost of performing machining operations by transferring the required skill of the operator to a machining device, thus making it possible for an unskilled worker to perform the operation. The advantages of commercial interchangeability has probably proven more important in many cases, however. Jigs and fixtures provide a very accurate method of locating holes and surfaces in relation to each other and to size within very close tolerances. This means lower cost of assembling parts without fitting and the possibility of supplying replacement parts for machines already in use. Even whe n the number of pieces is rather small and the cost of a jig or fixture does not seem warranted, they may be necessary for a saving in assembly time, duplication of the part and machine performance. Many items enter into the proper design of jigs and fixtures that are not apparent to the casual observer. A 16 finished jig op fixture may seem to he nothing more than rough castings or built-up pieces of steel with a few rest buttons and clamps to hold the part in place • The time and care which the tool designer has taken to lay out the jig or fixture and the accuracy with which the toolmaker has made the tool cannot be seen, but the real value can be easily determined when the tool is put into use. A careful study of the various suggestions for jigs and fixtures of different kinds as well as the principles involved will help in designing tools that are both sound in design and economical. Difference between jigs and fixtures. There is more or less cnnfusion regarding the terms used in describing jigs and fixtures. The terms jigs and fixtures are often used interchangeably, although there is a fairly well defined difference, generally agreed upon, between them. Most shop men are apt to use the term jig to describe most work-holding devices• This seeming lack of universal definition probably is due to two reasons: 1. An attempt is often made to form an all-inclusive definition to include devices actually misnamed in the shop. A tool with a guide bushing to hold the work and drill is called a jig. An apparatus to 17 hold the work while welding, assembling, and polish­ ing are often also called jigs. Although these devices are very dissimilar they are often called by the same n a m e . 2. Often an attempt is made to create the impression that jigs and fixtures are vastly dissimilar, which is not true. Actually there are any number of hybrids having the outstanding features of both. A jig is generally defined as a device for holding the work and guiding the tool while the operation is being per­ formed. In the true sense the term wjigw is applicable only to contrivances used in those processes in which the tool rotates and Is guided to the work as In drilling, reaming, boring, and similar operations. A jig is seldom fastened to the machine on which it is used, but is movable so that the tool can be aligned In the guide bushing. Fixtures are generally defined as devices for holding the work while an operation is being performed. They differ chiefly from jigs in that they do not guide the tool. Fixtures are usually fastened to the machine, thus establishing the proper relationship between the work and the tool. Fixtures are principally for work being performed in milling, broach­ ing, or planer machines. The term also may be correctly applied to welding or assembly devices that hold parts in the proper relation to each other while a fastening process is being performed. 18 Elements of jig and, fixture design* There are many more things to consider in the design of jigs and fixtures than seems apparent from the simple definition* The purposes that these devices serve can he broken down into many separate functions and each must be given careful design consideration. It will be found that the purpose of a fixture may be any except the first and fourth items in the list below. The jig may have any or all of the following p u r p o s e s 1. To guide the tool 2. To locate the work 3. To clamp the work 4. Secondary operation features 5. Chip control 6. Coolant control. Guiding the tool. only in a jig* Contact guiding of the tool is used Such guiding of the tool is used in drilling, reaming, countersinking, counterboring and similar operations. The guide for the tool is called a jig bushing. It, however, not only guides the tool but also keeps the tool in proper relationship to other holes to be drilled or reamed. Although jig bushings are made of hardened steel, they are very often subjected to severe wearing conditions and do become unserviceable in time. Consideration should be given 5 J. I. Karash, Analysis of Drill-Jig Design. New York: McGraw-Hill Book Company, 1944, p. 2. 19 to the necessity to replace these hushlngs w h e n the jig is designed, since some types of bushings are much easier to replace than others. Jig bushings have been standardized and can be purchased from any number of manufacturers who specialize in these items* Bushings are made in many types, the most common of which are the press fit and the renewable types* Press fit bushings are assembled permanently into posi­ tion and when worn out cannot be readily replaced. Therefore, they should be used only in low volume production or where the service is not severe. bushings: There are two types of press fit the plain or headless and the shoulder bushing. The plain type of bushing does have certain advantages. Besides being slightly less in cost and being flush with the top of the jig, they can be set closer together than the shoulder type. The main disadvantage of the plain type is that they are apt to work out of the jig plate either by the drill and pressure or because they are bumped with the drill press spindle. Renewable bushings are made in two parts, the liner or outer sleeve which is pressed into the jig plate, and the inner slip bushing used to guide the tool. There are two types of renewable bushings, the plain and the slip. The plain bushing is used where several bushings are required during the life of the drill jig, but are intended to be kept in place until worn out. The slip type can be pulled out to 20 facilitate multiple operations such as drilling* reaming* and spotfacing* or where the same jig is used for different drill sizes* Renewable bushings are used where the drilling action is severe and the bushings are apt to wear out before the jig becomes obsolete* When the wear is such as to cause inaccuracies* the operator can easily replace this type of bushing* Bushing clamps or lock screws are used on all renewable bushings to hold them in place and to prevent rotating* If the bushing is not clamped it will be drawn out by the drill. Clamps are intended for use in places where removing is infrequent. The lock screw type is the one to use where quick removal and replacement is desired* Typical jig bushings, liners, lock screws and clamps are shown in Figure 1. A number of typical bushing* liner* lock screw* and clamp installations are illustrated in Figure 2. Locating* A sound understanding of the principles of locating is a most important point to the designer* The fundamental purpose of the jig and fixture is to establish a desired relation between the work and the cutting tool within predetermined limits. If the jig or fixture fails in this one respect, the work produced will be scrap. Most important are that good facilities are provided for locating the w ork and that the part to be machined m a y be easily Plain renewable Slip renewable bushing bushimg Press fit bushing Head type liner Headless type liner Lock screw and clamp FIG.1- TYPICAL JIG BUSHINGS, LINERS, LOCK SCREWS AND CLAMPS Press fit headless bushing Screw lock Headless liner Flush mounting Screw lock Shoulder liner Flush mounting Press fit head type bushing Round end clamp Shoulder liner Flush mounting Round end clamp Shoulder liner Projected mounting FIG.2- TYPICAL JIG BUSHING, LINER, LOCK SCREW AND CLAMP INSTALLATIONS 25 located and quickly taken out of the jig or fixture* By all means, jigs and fixtures should be made foolproof so that it is impossible to insert the part except in the correct way* This is important to prevent errors, especially where a great deal of unskilled labor is used* The locating points should be visible to the operator so that it can be seen that the w o r k is properly seated before it is clamped in place. Since locating points in the jig or fixture may wear from contact with rough surfaces, they must be hardened steel and made conveniently replaceable by some means by the designer. There is no one best w a y to locate work in a jig or fixture. The method to be selected depends primarily on the piece that is to be machined* On some work, such as castings or forgings, w ork rest buttons would probably be used. In still other cases, as in partially machined blocks, rest buttons or relieved strips or plates m a y be the best selection. One of the most useful means employed in jig and fixture construction for locating or centering the part is the WV M, its construction varying to suit conditions. The term WV W block includes a wide variety of forms but is confined to the use of two Surfaces in contact with the work. This type of locator is especially useful on cylindrical shaped work. It can also be used on castings and forgings of cylindrical section, but in this case the knife edges or a short HV f*. should be machined with The reason for this Is that as 24 small a n area as possible of the part should come In contact with the locator. Better yet, when a "v,f Is to be used on castings or forgings, is to use an adjustable WV H as shown in Figure 5* This type of locator will allow adjustment to fit the casting, because castings or forgings often vary in size in different runs. If the work has not been previously machined, locating must be done from a rough or unfinished surface. In this case, not more than three fixed points of support can be used. Other supporting points or wjacksw m a y be used but they must be adjustable to compensate for the rough surface and are usually brought into contact with the work after clamping. The rest buttons and locating surfaces on which they rest should be either cone pointed or knife-edged* If the part has undergone a machining operation and has a finished surface, it may be wise to take advantage of this surface and locate on it. This part should rest on four buttons all the same height or on a relieved flat surface as illustrated in Figure 4. If the part, when located on the four buttons, does wobble or rock, this is a n indication that there is a chip or dirt on the locator or the part. In Figure 5 is shown two simple fixed or non-ad jus table stops, the type which are usually used on work that has been previously machined. In Figure 6 are adjustable stops that can be moved to compensate for variations in finish stock FIG.4- EXAMPLES OF RELIEVED LOCATORS 25 ---- 1 i-------- j£ -J FIG/S- TWO SIMPLE FIXED OR NON-ADJUSTABLE STOPS II — rr *C-~ ~ J FIG.6- ADJUSTABLE STOPS THAT CAN BE LOCKED IN POSITION 'I »i__ __ I —t FIG.3-REST BUTTONS OR JIG FEET FIG.,7- FIXED STOP WITH TWO POINT BEARING 27 left on castings or forgings* Many times the stop Is used to square u p the work piece by having contact at two separated points such as the stop Illustrated In Figure 7 . The rest buttons should be of sufficient height to allow room below the locating surface for chips. In Figure 8 is shewn two common types of buttons which can be used either as rest buttons or as feet on jigs* There is one very simple and efficient way in which to design a milling fixture. There are many cases where simple vise jaws can be designed to fit a standard milling machine vise either of the screw or quick clamp types. These vises are usually of substantial design and rigid construction and are very useful when supplied with properly designed jaws. These fixtures can frequently be used in place of expensive milling machine fixtures which, in many cases, are nothing more than special vises. In Figure 9 is illustrated a typical milling machine vise and some production type jaws. Clamping. After having the part correctly located, the next consideration is the question of how it is to be clamped in position in a n efficient manner. The proper designing of the clamps is a very important part of the designer's work. Faulty clamps may easily cause much defective work as well as injury to the operator due to broken tools and uncontrolled motion of the work piece. A clamp according to one dictionary is something that holds or binds things together. The Cam operated milling Vise with one machine machine wedge Jaw vise Vise Jaws for square parts Vise Jaws for flat parts ij Clamping two bars at once Hound p a r t ' d a m p e d in vertical V Jaw FIG.9- MILLING MACHINE VISE AND TYPICAL JAWS 29 application of the clamp in jig and fixture design is to hold parts in position during machining. This holding of the work piece for machining must he a complete restriction of any possible motion during the work operation. This means a restriction of movement in the vertical as well as the hori­ zontal plane, and also preventing of any possible rotation of the part. In designing a clamp to do these things, the designer must take into consideration the operation being performed. The force exerted on the work by the tool and the direction of the force must be determined. More ingenuity and originality can be displayed b y the designer in devising clamping means than in any other phase of jig and fixture design. A good clamping device must fulfill these requirements. First, it must hold the work piece rigidly while the tool is cutting. Second, It must clamp and unclamp with a minimum of effort in the shortest length of time possible. Third, the clamp must be positive regardless of vibration, tool chatter or heavy pressure. Fourth, the clamp must not damage the w ork piece in any way. The work must be held firmly in the jig or fixture w i t h ­ out distortion or springing and each succeeding piece must be held in the same position. To this end, the gripping and holding must be done nearly above or opposite the locating point and as near as possible to the machined surface. 30 The clamping means must be positive and rapid, yet simple in construction and operation* Screw clamps are very positive in action but are usually too slow for general use* When it is found necessary to use screws they should be operated with hand wheels or knobs* Often screw clamps on large jigs and fixtures are operated with power wrenches* Cams and eccentrics are very satisfactory clamping means; both are positive and rapid acting* The most used of all clamps is the plain screw and strap, and their combinations* Four of the simpler clamping devices are shown in Figure 10. Other clamping principles are illustrated in Figure 11* Several other types of clamping devices used in jig and fixture design are: Quick acting screw Cross-head screw Hook bolts Toe clamps Swing hook clamps Wedge clamps Lever clamps Cam locks Straps Spring pins latch clamps Toggle clamps Eccentric pins Rack and pinion Many of the various forms of clamps and jig and fixture details have become standardised and can be purchased from companies who specialize in this type of equipment. are many advantages to be derived There from such standardization. Mass production of these items greatly lowers cost. The use 51 .4_ 1 ' .J ^ pm * ^ Strap clamp II I ILU Handknob clamp Cam clamp t Swing clamp lir-J Fid. 10- FOUR STANDARD TYPES OF JIG- AND FIXTURE CLAMPS r I ! 32 Work Work Feed Poor Good — Cutting pressure against solid stop i£0 maximum Too close Handknob Handknob Poor Good Allow sufficient hand room Clamp Clamp Work Work Rest button Poor Good Clamp over rest button FIG*11- CLAMPING PRINCIPLES 33 of these items also greatly simplifies the design and ™«.i m T*g of jigs and fixtures* Standardized items Include various types and sizes of clamp assemblies, jack locks, flanged nuts, handknobs, keys, hardened washers, clamp rest, cams, spherical and ”0" washers and rest buttons* The designer should be well acquainted with these Items available and select the correct ones for the particular design whenever possible* Secondary operation features* When It is necessary to perform secondary operations, that is, drill, ream, tap, counterbore, countersink, or spotface, there are certain mechanical features that can be built into the jig that will greatly facilitate the performance of this type of work* The jig will probably offer no special secondary operation features unless the designer has deliberately built into the jig such features* For example, many times after drilling a hole seme second operation may be needed, such as reaming, tapping, or counterboring* In many cases there may be several operations to finish one hole as drill, countersink, and tap* In this case some special consideration will have to be given to guiding these tools or providing the necessary clearance for the tools* The use of a liner and slip bushing In drilling is one w a y of providing for a secondary operation* After drilling, 34 the hushing can he removed and a different size Inserted to guide a reamer, counterbore, or a drill used as a counter­ sink* Quite often the second operation tool can be used ungulded, but consideration must be given to the internal diameter of the liner bushing to Insure that the tool will pass through it* Three typical secondary operation setups are shown in Figures 12, 15 , and 14. It m a y even be necessary to make the bushing plate movable to facilitate use of the second tool* In Figure 15 are shown four operations which often are done In succession* By the use of flipper bushing plate the casting can be drilled, reamed, spotfaced, and chamfered all in one jig* There are many variations and combinations of tools and jigs features such as these which, if properly designed, prove very useful* Chin control* Of all the factors involved in the process of jig and fixture design, that most overlooked or neglected Is the subject of chips. A jig or fixture may be well designed from the standpoint of locating, clamping, etc., but the operation of it is inefficient because minor con­ struction details pertaining to chips had been overlooked. This creates a most trying and tedious job for the operator* It probably has been noted some time that in some drilling operations much time Is often spent In breaking up 35 Drill Reamer FIG.12- DRILLING AND REMOVING SLIP BUSHING FOR AN UNGUIDED SECONDARY OPERATION Drill Counterbore FIG.13- USING TWO SIZES OF SLIP BUSHINGS FOR DRILLING AND COUNTERBORING WITH FLAT POINT DRILL Countersink 1 s is s Y 1 i \ y / x \ 1, m . FIG. 14- USING TWO SLIP BUSHINGS TO DRILL AND COUNTERSINK WITS THE END OF BUSHING GUIDED DRILL 36 / Drill o Reamer T 11 o; LJ Drilling Unguided Reamer Spo facer Countersink Piloted Piloted Spotfeoer Countersink PIC. 15- AN EXAMPLE OF THE USE OF A FLIPPER BUSHING TO FACILITATE THE SECONDARY OPERATION 37 and removing chips to allow continuation of the operation* A drill jig can he so designed as to minimize or even eliminate the time that would ordinarily be required for this purpose* Much of this chip trouble is caused by a n improper relation between the bushing and the work* In Figure 16 is shown some examples of the different placements* If the bushing Is at the proper distance from the work, the chips will have ample room to get out and not tangle the work* If the bushing is improperly placed, as in the other views of Figure 16, it is quite obvious that the chips are going to pack up and cause considerable trouble* In the designing of jigs and fixtures it is at times advantageous to provide grooves or troughs In the locating corners so as to avoid locating misalignment that might be caused by chips* There are seme examples of what is meant b y wcorner relief” In Figure 17* Often serious chip interference can be avoided by using the proper contact area relief on the locating surface. When two flat surfaces come together, a single chip between them will prevent them from caning into full contact* The entire area of these contact surfaces is vulnerable to a single chip. If the locating surface is relieved or cut away except for narrow strips so that the contact area Is small, the proba­ bility of a chip being on this area would be greatly reduced. 38 Drill Drill Boshing Bushing Chip Clearance Bushing too close to work Proper placement of bushing Drill Drill Bushing Bushing No chip clearance Inaccuracy caused by excessive chip clearance FIG.16- PLACEMENT OF THE BUSHING 39 U CONTROL 000 to 10,000 surface feet per minute. There are probably more different types of grinding machines than any other one type of metal cutting machine. In many cases, It Is almost impossible to draw a clear line between many of the different types of grinders. There will be no attempt to establish standards of classification, but to promote an understanding of the common production machines and their functions. The most common types of production grinders are: Cylindrical Centerless Surface Internal Thread Cylindrical grinder. The cylindrical grinder is the most common grinder used on production. Work that Is round in cross section is usually ground on a cylindrical grinder. This type is used to grind such pieces as plain cylinders, contoured cylinders, tapers, faces, shoulders, fillets, and even cams and crankshafts. The cylindrical grinder is shewn in Figure 35 • As in any other machine, there are certain essential movements 109 110 Involved* In the cylindrical grinder, the work must revolve, the grinding wheel must revolve, and the work must pass the wheel, or the wheel must pass the work. Also there must be some method of feeding the wheel Into the work, or the work Into the wheel. If the work piece is long, it is mounted between centers and driven by a dog much as in an engine lathe. Short work, castings or forgings can be mounted on a faceplate or held in a chuck or suitable fixture. Provision is made to traverse the work back and forth in front of the wheel. This move­ ment is accomplished manually or automatically by dogs which cause the table to reverse at the end of each stroke* In this type of operation the work is mounted between centers in the headstock and tailstock which are mounted on a table which reciprocates in much the same manner as the milling machine table travels. A separate motor is provided in the headstock to rotate the work. The grinding wheel is mounted on a spindle and driven by another motor through belts so that it is isolated from vibrations of any kind, particularly frcaa the drive motor. The whole motor and wheel spindle assembly is carried on a slide, which is adjustable in and out to suit the diameter of the work. The infeed of the wheel to the work is done automatically on many machines, so that a predetermined diameter can be reached and repeated without hand adjustment. 1X1 Even compensation for grinding wheel wear is built into many machines* As with man y machines of the turning and milling machine groups, the cylindrical grinder can be set up with a com­ pletely automatic cycle so that one operator can tend several machines* Automatic sizing is an important feature in this type of arrangement* After one part has been completed the wheel retracts and is redressed as required to hold size* Continuously reading gages are often used by this type of grinder* In this arrangement dial gages are supported on a holder above the work and near the wheel* up w i t h a zero* This gagels set When the work is being ground the gage has contact with the work and the amount of stock to be removed can be read instantly without stopping the work. When the dial reads zero the work is the size of the master, thus to the proper size. The grinding wheel is dressed with a mounted diamond* In the cases where two to five wheels are used for the purpose of producing several stepped or contoured sections in the part at the same time, the diamond dresser may also be used* If a contour is desired the wheel can be crushed or dressed with a hardened steel roll of the desired shape* The speed of the grinding wheel should be from 5500 to 6500 surface feet per minute, or a shop man likes to remember it slightly over one mile a minute. The speed of the work 112 Is usually from 30 to 100 surface feet per minute depending on the hardness of the material# in general, the work speed is reduced for the harder steels. The modern cylindrical grinder is a heavy, rigid, accurate machine capable of producing part diameters accurate to approximately #0001 inches. The parts are also equally accurate in roundness and straightness. Center less grinders. Center less grinding machines make possible the finish grinding of pieces without supporting them at their end with conical centers. The distinguishing feature of this machine is the two wheels, one the grinding wheel and the other called the regulating wheel. these is the work rest blade. Between The piece to be ground is supported on the work rest blade, which has a top surface sloping away from the grinding wheel, and against the regulat­ ing wheel rotating at slew speed. The speed and friction of this wheel keeps the work rotating uniformly as it is ground. A modern center less grinder such as this is shewn in Figure 36* There are two methods of center less grinding; that is, either by through feed grinding or by infeed grinding. In through feed grinding the work pieces are fed straight through the space between the wheels. To impart endwise motion to the piece, the regulating wheel is tipped on its axis at a FIG. 36-A MODERN PRODUCTION GRINDER TYPE CENTERLES8 113 114 slight angle, which results in the piece moving like a screw* This type of* grinding is best adapted to continuous automatic grinding of* parts of* constant diameter* Infeed grinding is used on that type of work in which the piece cannot he passed between the wheels* This type of work might be such things as tapered, formed or shouldered work* The work is placed on the rest blade and against the regulating wheel* part is located endwise with an end stop* work is plunge ground. The In this case the Both types of centerless grinders are high production machines* These machines can easily be converted back and forth from one type to the other* Straight, taper, formed or multiple diameter work of almost any material, metallic or non-metallic, can be ground within extremely close limits or accuracy and surface finish. Straight cylinders, piston pins, dowels, valves, tubes, and straight shafts and other hardened parts that cannot be held on centers or chucked without difficulty can be finished on a centerless grinder. The advantages of centerless grinding are that no time is needed to chuck or center the part, it increases the accuracy of the grinding process and takes less grinding time. A good example of the type of work performed and the accuracy possible is the grinding of piston pins which have been finished to .00005 inches by this process. 115 grinders* Surface grinders can be distinguished by the position of the grinding spindle and the shape and movement of the workholding table* There are two types of spindles in surface grinders; that is, a vertical and hori­ zontal spindle* or rotary* The table motion can either be reciprocating The motion of the table is usually in a horizontal plane, an exception being in the case of a disc grinder which is usually considered a special purpose machine* On the horizontal spindle reciprocating table machine the grinding is done on the periphery of a straight wheel. Small fixtures can be fastened Onto the table to hold the work* These fixtures can be bolted down in the one or more keyways. This machine is often used with a magnetic chuck on the table. With this fixture many small parts can be placed on the table and ground at once* also be held with the chuck. Small fixtures can Besides being used on pro­ duction, this machine finds wide usage in the tool room. The vertical spindle, reciprocating table machine uses a cup or segmented wheel and cuts with the side or end of the wheel. This machine is capable of removing a great deal of stock rapidly whereas in the horizontal spindle machine the cut is rather light. This is a heavily built, large machine and is used almost exclusively on production and very seldom in the tool room* This is partly because this machine cannot equal the accuracy of the horizontal spindle 116 machine* The vertical spindle, rotary table machine uses the same grinding wheel as the reciprocating table machine. This machine is the most adaptable of* all the surface grinders to mass production methods. Because of the rotary motion of the table, work can be ground continuously and auto­ matically. Autanatic hoppers or loaders ani take-off devices are often fitted to the machine. The horizontal spindle, rotary table machine grinds with the periphery of a straight wheel. The spindle can usually be tilted to grind concave or convex surfaces. This is not a machine that is used in general shop work, but Is usually adapted to a special application. Internal grinders. Internal grinding as the name implies is the process of grinding the interior of a cavity or hole. The internal cylindrical surface Is completed by reciprocating a rapidly rotating grinding wheel back and forth In the hole as the work piece revolves slowly. The grinding wheel diameter does not correspond to the diameter being ground, but is smaller. The wheel center is offset with respect to the work center and size is controlled by a lateral cross feed movement of the work head slide. A typical internal grinder Is shewn In Figure 37• Note the position of the work head and the grinding spindle. The work is held in a chuck or a workhoiding face plate fixture and In some cases In a collet. Quite often the chuck or fixture Is air or 1V7 118 hydraulic ally operated* The grinding wheel is driven by an electric motor belted to a high speed grinding spindle by an air spindle or by a high speed electrically driven spindle* The speed of the grinding wheel may vary from approximately 10,000 to 100,000 RFM* Any type of work piece requiring an internal diameter to be held to exacting tolerances or finish can be done on this type of machine * Thread grinders* The thread grinders are used for a wide range of small lot work as well as for long production runs* Continuous and multiple internal and external, right and left hand, straight, tapered, and relieved threads can be ground in any pitch in standard threads, or special thread forms can be ground on internal or external work* Thread grinders are for the grinding of internal and external threaded parts requiring high commercial accuracy* These machines can be made to run completely automatic except for the three simple manual steps of loading, shifting start lever and resetting grinding wheel* Automatic functions include wheel dressing, wheel size compensation after dressing, wheel feed, retract, backlash compensation and work speed control for roughing, finishing, and rapid traverse* Making threads "from the solid” on hardened blanks, and easily threading parts of material difficult to thread by other methods are some of the advantages that thread grinding 119 makes possible In production requiring accurately threaded hardened parts* Threads on previously roughed work pieces can be matched to the grinding wheel by means or a built-in lead pick-up* The part may be grouni in both directions of the work spindle rotation* There are several advantages to thread grinding besides being able to cut from hardened material* Threads ground from the solid do not have hardening cracks, and the tearing always present to same extent in any other material removal method* Distortions due to heat treatment may be eliminated by grinding from the solid after hardening. Aircraft engine part threads which demand high accuracies and freedom from distortion and stress cracks are produced in this manner* Whether grinding fine threads from the solid or coarse threads that have previously been roughed and heat treated, a tolerance on the pitch diameter of plus or minus .0002 can be held with manual operation, and plus or minus *0003 with automatic stop and dress control. Leads can be held to plus or minus .0002 in any inch or plus or minus .0005 in any 12 inches* An external and internal thread grinder are shown in Figures 53 and 59* 120 FIa.38- EXTERNAL THREAD GRINDING MACHINE FIG.39-INTERNAL THREAD GRINDING MACHINE VI. PLANERS, SHAPERS AND BLOTTERS There are three variations of* machines that incorporate the straight back and forth motion of the tool with respect to the work or the work with respect to the tool. The planer, shaper and slot ter all belong to the same class of machine because in each a flat surface is machined with a single point tool. In the planer, the tool is stationary and the work piece moves past it, but In both the shaper and the si otter the work Is stationary and the tool moves past it. All three machines are used to machine a flat surface but the selection of the proper machine will depend on the size, quantity, and the nature of the work. For large work the planer is about the only machine that can be used. With rather small parts to be machined, the choice might depend on the quantity. If the quantity Is rather small the shaper would be the machine to be used, but if the quantity is large, a great number can be set up on the table and machined at once on the planer. Also, if the number is large, the milling machine might be given consideration depending on the cutter and machines available. There is one factor that many times enters into the selection of the planer over the milling machine and that Is the quality of castings to be machined. Often in a small run of castings the quality may 122 be a little below standard. dirty, sandy and scaly. They may tend to be rough, If this is the case, the planer would be selected because with a milling machine expensive cutters would be ruined. The slotter may also be called a vertical shaper because the action is the same as the shaper but the ram carrying the tool moves vertically. ram can be set at an angle. In some tool room models this This machine is especially useful In work requiring machining of a flat surface at right angles to the main base. Such a work piece would be difficult to set up on either the planer or shaper. The slotter has been largely superseded by the vertical milling machine in most shops except in some of the railroad shops where their type of work lends itself well to this machine. VII. BROACHING MACHINES The broaching machine and broaches are a development and a result of high production manufacturing. The broach­ ing machine does what could be done on one or a combination of the basic machine groups, driller, millers, lathe or shaper, but at a much greater rate. In any discussion of broaching machines there must first be a basic knowledge of the broaching process. Broaches are metal-cutting tools with a series of teeth in which a gradual rise In tooth circumference or height allows each successive tooth to remove only a predetermined amount of stock as the broach Is moved past or through the work piece. Each tooth cuts a specific amount of metal until the last teeth have produced a form of the exact shape and size required. Unlike other cutters, each tooth on a broach is in contact with each part only once and cuts only a small portion of the entire stock removed. The advantages of broaching over other methods are: speed of stock removal, high finish, and close tolerance, which can be maintained consistently. Broaching is economical on high production operations and low production where quality of finish and close tolerance is required. There are two classifications of broaching operations: internal and surface broaching. Internal broaches are used 124 to broach round holes, splined holes, Irregular shaped holes such as hex, squares, rectangular or any contour. Surface broaches are generally of slab or sectional construction and are mounted on broach holders which are adapted to the machine ram* Surface broaches may be designed to broach half round, cams and various shaped contours. There are several ways of forcing the broach through or by the metal* The two most common methods are pushing the broach or pulling it -- giving rise to the term ”pull broaches11 and ”push broaches”* In addition, certain types of surface broaching are often performed by drawing the work across the broach. There Is no limitation to the form of a broach tooth and so there is no limitation in the shape of broached surface. The only type of surface that cannot be broached Is one that has an obstruction that interferes with the passage of the broach. There are four broad classes of broaching machines in use today. work. The horizontal machine is used mostly for Internal The vertical pull up or pull down machine Is also used primarily for Internal work. best adapted for surface broaching. The vertical machine is The fourth type, the hydraulic press, Is used for push broaching. Any broaching machine, however, may be used for a variety of different operations* For example, a horizontal machine can be adapted for surface broaching by the proper design and construction 125 of the broach and fixture. In much the same way a surface broaching machine can be set up to do internal work. In addition to the previous mentioned broaching machines, there Is one type that is somewhat special in nature and is seldom used except on high production. In this machine the work is pulled across the broach or broaches. In Figure 40 is shown this type of machine and in a close-up of the broach holder and fixture can be seen how this Is done. In this particular machine the broaches are stationary in the head and the fixture mounted on a chain carries the work piece • VIII* HONING, LAPPING AND SUPERFINISHING There are three methods to obtain the ultimate in fine surface finishes on metal parts and for obtaining extremely close dimensional accuracy or optical flatness* These methods all use abrasives in one form or another, but not in the form of a grinding wheel* The three machines used for this purpose are the hone, lapper and the superfinisher* Hones• The honing machine in many cases is much like the vertical drill press in appearance* however, is very much different* The spindle motion, The honing machine spindle rotates rapidly while being reciprocated up and down at the same time but at a much slower speed in feet per minute* Honing is an abrading process used to shear stock from a cylindrical surface* It Is used largely for removal of tool marks and as a final finish process for cylindrical bores and other bearing surfaces* The hone consists of a series of four or six abrasive sticks mounted in a circle in a steel holder. As the tool is expanded these sticks are forced out radially with equal pressure in all directions. With all the sticks in contact with the surface the tool is stabilized in the cylinder and thousands of grits abrade a large area simultaneously* The work Is clamped In a stationary 128 position on the table usually by means of a fixture. The hone is allowed to float freely, and does not generate align­ ment as related to squareness, concentricity or parallelism of axis In adjacent parts. The hone tool will correct taper and out of roundness in the bore, and will generate a true cylindrical bore. Accuracy of roundness Is generated by the rotary motion of the hone, and accuracy for diametric straightness is generated by the reciprocating motion always given the hone. The speed In the honing process ranges from 10 to 250 feet per minute. From .003 to .0045 of stock is removed when honing a cylindrical bore. The hone is used to finish bores in engine cylinders, air and hydraulic cylinder sleeves. Any machineable material and many materials ordinarily considered unmachineable can be honed. These include all types of cast iron and steel, all non-ferrous metals, ceramics, glass and seme plastics. Tappers. Lapping Is a name given several methods of producing fine finishes on ground parts. The process may be either machine or hand operation. There are two general types of lapping machines in use: the vertical and the centerless. The centerless is used exclusively for cylindrical work whereas the vertical can do either cylindrical or flat pieces* The vertical lapping machine Is arranged with two round cast iron laps or disc in a horizontal plane. The upper lap 129 Is free to float in small machines to adjust itself to the work, hut In large machines Is power driven* The lower lap is rotated in all cylindrical lapping, for most flat lapping and for dressing* The work to be lapped Is placed between these two laps, the top lap Is lowered to apply a slight amount of pressure on the work, and the laps rotated. The proper grade and grit of lapping compound is applied to give the desired finish. Generally the abrasive is contained In oil* The other common type of lapping machine is the center­ less lapper. This machine is somewhat similar to the center­ less grinding machine in that it has two driven wheels, or rolls that turn at different speeds. These machines may vary in size from small bench models to a machine as large as a centerless grinder. The work piece is placed between the rolls with a slight amount of pressure and the proper abrasive and allowed to rotate until the desired finish and size are obtained. Compared with grinding the speed is very slow and usually only a few millionths of an inch of material are removed. Most fixed size gages as plug gages and gage blocks are lapped. Lapping Is particularly efficient for production of size blocks, plug gages, sides of ball races and thrust washers. Valve plates, the component parts of metering pumps, hydraulic pump parts, refrigerators, compressors, and diesel 130 engine Injectors are some of the many other parts also in this category. Superfinishing. SuperfInlshing is a form of lapping that reduces surface Irregularities left by grinding to a few millionths of an inch variation from the geometrically true cylindrical sxirface. One of the objects of superfinlshing is to remove metal deformed by the previous operation, such as grinding. In general purpose type of superf ini sher, the work Is supported between centers as in a lathe and rotated at moderate speeds. A power driven mechanism at the rear carries the stone holder and provides means of applying pressure on the stones and for reciprocating the hdder back and forth with short rapid motions, also means for slowly traversing along the work. Bonded abrasive sticks similar to hone sticks are used but the motion is over an irregular path so that no one point on the stone crosses its cwn path again. In many cases this process is accomplished without a superfinishing, but Instead Is done on a regular lathe with a superf inlshing attachment mounted on the cross slide. This process is necessary in some cases depending on the function of the part in the assembly. In grinding, each abrasive particle of the grinding wheel acts as a very small cutting tool and shears off metal In small chips • This means 131 that the surface of the metal has been subjected to a com­ pressive force sufficient to exceed the compressive limit of the metal. Thus, even on a finely ground surface there is a thin layer of stressed and deformed metal. Grinding and other common machining methods have been shown to be of value as dimension creating operations, but surfaces produced by such means definitely cannot be regarded as being sufficiently true to be wear resistant. Superf inlshing will more completely produce the required type of surface than any other method. This type of finish Is efficient in the surface refinement of cylindrical, spherical, conical, or taper shaped parts. Although it is not primarily a dimension creating process, it is necessary that some little stock be removed, averaging .0001 to .0002 on the diameter to remove the spurious layer of stock. A positive pressure is not used; the abrasive is held in place on the work by a rather flexible force of 10 to 40 pounds per square Inch. This process is not to be confused with grinding where surface speeds range around 6000 feet per minute. In superfinishing the speed seldom exceeds 8) feet per minute and is approximately 50 to 60 feet per minute. In all cases the work Is flooded with coolant to carry off the heat generated. Crankshafts, clutch plates, valve stems, piston pins, and rocker shafts are only a few of the representative auto­ motive parts superfinished. IX. SPECIAL PURPOSE MACHINES One of the first factors essential to interchangeable manufacturing is the use of machinery in the place of hand work. Often It is advisable to use a machine other than the general purpose drilling, turning, milling, grinding, and shaper groups. Usually this machine and the work that it does is quite special in nature as contrasted to the general nature of the work performed by the standard machine* This type of machine Is designed to do a specific operation or operations on a particular part of a given design. This type of machine is called special purpose because if the design of the work piece is altered radically, the machine must be almost completely rebuilt to be of further service in making the revised design. The work piece might be almost any manufactured part. For example, the work piece might be an engine block and the machine might be built to bore, ream, and hone the cylinder bore and at the same time the stud holes could be drilled, countersunk and tapped. In nearly all cases several operations are being performed on the work piece at one time or several different operations are done In succession. In Figure 41 is shown a typical special purpose machine that was designed to tap,drill and countersink in the first station, 133 F I G . 4 1 - SPECIAL DRILLING, COUNTERSINKING,AND TAPPING MACHINE 134 to drill an oil hole in the second station and to tap in the third station. The fixture in the center indexes and has one loading station and three working stations. are machined at one time. Eight parts Note that the upper columns are standard drill press heads with special multiple spindle drilling and tapping units. These standard heads are mounted on a cast base. The special purpose machine may offer many advantages over the general purpose machine in specific cases. Some of the advantages such a machine may offer are as follows: 1. Obtain full production with unskilled labor 2. Conserve manpower 3* Cut production cost 4. Reduce floor space 5* Increase tool life 6. Maintain exacting accuracy 7. Produce with smaller capital invedment. The special purpose machine applies low cost continuous production to a wide variety of work In much the same way as small parts are produced on automatic screw machines. Frequently a group of operations Is consolidated in a machine to eliminate two or more other machines and thereby save labor. These machines are made to complete any one or a combination of turning, milling, drilling, boring, reaming, tapping, and grinding operations automatically. As complicated as some of these machines may look, a man can 135 be trained to operate them in a few hours time, and relatively unskilled workers can operate them* Accuracy Is built into the machine to eliminate the human error and thereby main­ tain precision tolerances even though the operator lacks skill and experience* As strange as it may seem, more skill is required to run a general purpose machine than a highly special one that need only be supplied with work. These machines are usually engineered with full automatic operating cycle to load, clamp, feed, unclamp and eject the work. Machines designed for a particular purpose are compact, self-contained production units which occupy less space than the machines that they replace and at the same time produce more work. They simplify the problems of economical plant layout and reduce handling. Another advantage of this machine is that It conserves tool life because the spindle speeds and feeds are fixed so cutters always operate under conditions most favorable to economy, and interlocking controls prevent breakage. Furthermore, the initial cost of this type of machine with all its automatic features is often less than the combined cost of a group of standard machines. These are all factors that must be given consideration In selecting a special purpose machine. Even with all these features this type of machine does have seme disadvantages that must be considered. Such machines take highly skilled mechanics to build and special tools and fixtures are needed 136 with them. It also takes highly Intelligent mechanics to maintain and repair them. Another factor that is all important in the machine decision is the length of the production run. On a special machine the total cost must "be amortized over the length on the run of the one work piece, because at this time the machine will be of little or no future value for production without extensive rework. In the case of the standard machine, when production is completed on one part, the cutters and the fixtures can be taken off and replaced by new equipment for a new work piece. In this way the machine cost can be spread over a long period making the machine cost for any one production part very economical. IV. SUMMARY As used in the foregoing sections of this thesis the term 1tool engineering” has become recognized as meaning the design and selection of the necessary tools and machinery for the economical production of a given quantity of parts or assemblies. In this general definition is included the two major objectives of concern to the tool engineering group: tool design and production machinery. The scope of this thesis Is limited to the discussion of these two objectives. Special emphasis has been placed on the ultimate production of manufactured goods by the most economical means, and the necessary procedures by which that end is attained. The essential purpose of tool design is to furnish designs and drawings of the necessary jigs, fixtures, and gages for the complete tooling of any desired part. General methods of tool design which enable the designer to develop ideas Into practical specifications for modern manufacturing methods form the basis of this section. Many graphic illustrations are Included to show the principles and problems Involved in tool design. While every tool designer is confronted by different problems, there are certain funda­ mental principles which can be modified to meet existing 138 conditions and applied to most cases. In the discussion of the design of jigs and fixtures, the problems were approached by considering the various purposes for which these tools are used, such as guiding the tool, locating the work, clamp­ ing the work, secondary operation features, chip and coolant control. Under each of these purposes were considered some of the principles and problems Involved. While the contents were aimed primarily at presenting general principles of design, many suggestions should help In the solving of technical problems. Also presented In this text is the objective of good tool design from the standpoint of motion economy. This Is very important for the most economical production of the work piece and an item over which a designer may have direct control. Motion economy in design deals with those factors which enable the operator to produce a work piece in less time. These items may include such things as to ehninate barriers, to provide sufficient chip clearance, and to provide quick and easy clamping and unclamping of the part. To tool engineering an industrial gage is an instrument to determine the dimensional fitness of a given work piece for subsequent operations or to function In the assembly of which it is a part. Since tool engineering is responsible for the design or purchase of all the necessary gages for production, they must have a complete knowledge of gages and 139 gaging, Including gaging principles, purpose, and classifica­ tion of gages. In general, all industrial gages can be classified into three groups as manufacturing gages, inspection gages, and reference gages. The personnel of the tool engineering division must also have a complete knowledge of all types of production machinery, both standard and special, for with them rests the responsibility of selecting or purchasing the necessary equipment for production. To do this efficiently the function, purpose, operation, advantages and disadvantages of each must be taken into consideration. The machine selected will depend on several factors, the principal ones being: the type of production, volume of production required, manu­ facturing equipment available, and the required quality of finish. Many photographs are included to supplement the descriptive material and to give the reader a better idea of the types of machines used in Industrial production. Besides the description of the general types of production machinery, advantages and disadvantages of the special single purpose machine is also Included. The ccmplete work and field of tool engineering has not been covered b y any means by this thesis. Hcwever, an introduction to tool engineering has been given which will be interesting to both the technical student and the practicing engineer. In the text of this thesis has been presented 140 background of industrial information that will give a better understanding of modern industry. Also was discussed the purpose, function, and seme of the "know-how” of the technical profession known as "tool engineering". BIBLIOGRAPHY Anonymous, Machine Design. December, 1944* Brickner, C. E. J., The Tool Engineer!s Place in the Industry Tool Engineer. July, 1946. p. 37* Hall Foundation, Herbert D., The Machine Tool Primer» New Jerseys Herbert D. Hall Foundation, 1943* 111, 137 174-181 pp. Hines, Charles R., Machine Tools for Engineers. New York: McGraw-Hill Book Company, 1950. p. 201. Karash, J. I., Analysis of Drill-Jig Design. New York: McGraw-Hill Book Company, 1944V Preface p. 2. Owen, Halsey, Introduction to Tool Engineering. New York: Prentice-Hall, Inc., 19^8^ 5-iO, 21-22 pp.