Machining Fundamentals From Basic to Advanced Techniques by John R. Walker Publisher The Goodheart-Willcox Company, Inc. Tinley Park, MlinoisMachining Fundamencals Copyright 2000 by THE GOODHEART-WILLCOX COMPANY, INC, Previous Editions Copyright 1998, 1993, 1989, 1981, 1977, 1973 All rights reserved, No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of The Goodheart-Willcox Company, Inc. Manufactured in the United States of America Library of Congress Card Catalog Number 99-1776 International Standard Book Number 1-56637-662-9 345678910 00 0302 0100 Cover photo OWestlight (K. Tiedge) Waker, John FL ‘Machining Fundamentals from basi to advanced techniques / by Jofn RWaiker pom. Includes indo. ISBN -56697-662.0 41, Macrine-shop paces, 2, Machining LTte soxrrs | op!Introduction Machinists are highly skilled men and women. They use drawings, hand tools, precision measuring tools, drilling machines, grinders, lathes, milling machines, and other specialized machine tools to shape and finish metal and nonmetal parts. Machinists must have a sound understanding of basic and advanced machining technology, which includes: ‘* Proficiency in safely operating machine tools of various types (manual, auto- matic, and computer controlled). « Knowledge of the working properties of metals and nonmetals. « The academic skills (math, science, English, print reading, metallurgy, etc) needed to make precision layouts and machine set-ups. Machining Fundamentals provides an introduction to this important area of manufacturing technology. The text explains the “how, why, and when” of numer- ous machining operations, set-ups, and procedures. Through it, you will learn how machine tools operate and when to use one particular machine instead of another. ‘The advantages and disadvantages of various machining techniques are discussed, along with their suitability for particular applications. Machining Fundamentals details the many common methods of machining and shaping parts to meet given specifications. It also covers newer processes such as laser machining and welding, water-jet cutting, high-energy-rate forming (HERP), cryogenics, chipless machining, electrical discharge machining (EDM), electro- chemical machining (ECM), robotics, and rapid prototyping. The importance of computer numerical control (CNC) in the operation of most machine tools, and its tole in automated manufacturing is explored thoroughly. This new edition of Machining Fundamentals has many features that make it easy to read and understand. A numbering system for headings has been adopted to make it casier to locate information in a chapter. Learning objectives are presented at the beginning of each chapter, along with a list of selected technical terms important to understanding the material in that chapter. Throughout the ‘book, technical terms are highlighted in bold italic type as they are introduced and defined. Several hundred of these terms are also listed and defined in a Glossary of ‘Technical Terms at the end of this text. Review questions covering the content taught are presented at the end of each chapter. Color is employed extensively in this new edition to enhance understanding and to emphasize safety precautions. A consistent color coding has been employed in the hundreds of line illustrations (most made especially for the text) to help you visualize more clearly the machining operations and procedures, Many of the black and white photographs in the text have been replaced with new, full-color photos showing the most current types of equipment and processes. Machining Fundamentals is a valuable guide to anyone interested in machining, since the procedures and techniques presented have been drawn from all areas of machining technology. John R. WalkerMachining Fundamentals Color Key Colors are used throughout Machining Fundamentals to indicate various materials or equipment features. The following key shows what each color represents. E| Metals (surfaces) Rulers and measuring devices | Metals (in section) Direction or force arrows, — dimensional information | | Machines/machine parts || Fasteners B Tools ® Abrasives we Cutting edges Fa Fluids a Work-holding and tool-holding devices & Miscellaneous IMPORTANT SAFETY NOTICE Work procedures and shop practices described in this book are effective, but general, methods of performing given operations. Always use special tools and equipment as recommended. Carefully follow all safety warnings and cautions (they are printed in red type for greater legibility). Note that these warnings are not exhaustive. Proceed with care and under proper supervision to minimize the risk of personal injury or injury to others. Also follow specific equipment operating instructions. This book contains the most complete and accurate information that could be obtained from various authoritative sources at the time of publication. Goodheart-Willcox Publisher cannot assume respon- sibility for any changes, errors, or omissions.Contents Chapter |. An Introduction to Machining Technology .. 1.1 The Evolution of Machine Tools. .... : 1.2. Basic Machine Tool Operation . ... 13 Nontraditional Machining Processes 14 Automating the Machining Process. 15 The Evolving Role of the Machinist Chapter 2. Shop Safety... . 2.1 Safety in the Shop . . 22 General Machine Safety 23 General Tool Safety . 24 Fire Safety Chapter 3. Understanding Drawings 3.1 Dimensions. . 32 Information Included on Drawings 3.3. Types of Prints..... 344 Types of Drawings Used in the Shop 35. Parts List... 36 Drawing Sizes . 37 Geometric Dimensioning and Tolerancing . Chapter 4. Measurement 4.1 TheRule. . : 42 The Micrometer Caliper . 43. Vernier Measuring Tools. 44 Gages .... 45 Dial Indicators . 4.6 Other Gaging Tools .....-- 47 Helper Measuring Tools . . Chapter 5. Layout Work .. 5.1 Making Lines on Metal 52 Squares... : 5.3 Measuring Angles a 54 Simple Layout Steps ........ 55 Layout SafetyMachining Fundan Chapter 6. Hand Tools ........+.+secee eee ee IE 6.1 Clamping Devices . 1 62 Pliers... 63 Wrenches ..... 64 Screwdrivers... 6.5 Striking Tools 69 6.10 6.11 Hand Polishing ........... Chapter 7. Fasteners . 7.1 Threaded Fasteners . cee 72 Nonthreaded Fastening Devices, 73 Adhesives. 74 Fastener Safety. Chapter 8. Jigs and Fixtures 143 B81 Jigs... : 143 82 Fixtures. 115 83 Jig and Fixture Construction, 146 Chapter 9. Cutting Fluids. . 149 9.1 Types of Cutting Fluids : 2149 9.2 Application of Cutting Fluids. -150 Chapter 10. Drills and Drilling | Macl 153 10.1 Drilling Machines ciceeecteeeees eee 138 10.2 Drill Press Safety . fesse BT 103. Drills. 104 Drill-holding Devices - 105° Work-holding Devices. ..... 10.6 Cutting Speeds and Feeds. 107 Cutting Compounds ..... 108 Sharpening Drills. 10.9. Drilling . : 10.10 Countersinking 10.11 Counterboring 10.12 Spotfacing. 10.13 Tapping. . 10.14 Reaming . Chapter 11. Offhand Grinding . ‘11.1 Abrasive Belt Grinders ....... M2 Bench and Pedestal Grinders . 11.3. Grinding Wheels . 114 Abrasive Belt and Grinder Safety 11.5 Using a Dry-type Grinder IL6 Using a Wet-type Grinder. 11.7 Portable Hand Grinders . 183 = 183 + 183 2185 - 186 187 «188 188table of Contents Chapter 12. Sawing and Cutoff Machines ....... 191 12.1. Metal-cutting Saws .. ee er 122. Reciprocating Power Hacksaw. 123 Power Band Saw . 124 Using Reciprocating and Band Saws 125 Circular Metal-cutting Saws . 12.6 Power Saw Safety ... Chapter 13. The Lathe 13.1 LatheSize.... 13.2 Major Parts of a Lathe 133 Preparing Lathe for Operation. 13.4 Cleaning the Lathe. ....... 13.5. Lathe Safety .... 136 Cutting Tools and Tool Holders - 13,7 Cutting Speeds and Feeds. 13.8 Workholding Attachments... 139 Turning Work Between Centers 13.10 Using Lathe Chucks. 13.11 Facing Stock Held in Chuck... : 13.12 Plain Turning and Turning to a Shoulder 13.13 Parting Operations. . Chapter 14. Cutting Tapers and Screw Threads on the Lathe ... 14.1 Taper Turning 142 Calculating 143 Measuring TTilstock Setover. 144 Cutting a Taper 14.3. Measuring Tapers . . 14.6 Cutting Screw Threads on the Lathe . Chapter 15. Other Lathe Operations .........- 261 15.1 Boring on a Lathe. ..... a --261 152 Drilling and Reaming on a Lathe +263 153 Knurling on a Lathe. : = 265 154 Filing and Polishing on a Lathe . -267 155. Steady and Follower Rests . = 268 15.6 Mandrels. . wee -.270 15.7 Grinding on v the Lathe. 270 158 Milling ona Lathe . 272 159. Special Lathe Attachments . 122 15.10 Industrial Applications of the Lathe . 274 Chapter 16. Broaching Operations. cence ee eee se 281 16.1 Advantages of Broaching -....... 283 16.2 Keyway Broaching. = 283Chapter 7. The Milling Machine............+.285 17.1 Types of Milling Machines . +286 172. Milling Safety Practices. -292 173. Milling Operations. 293 17.4 Milling Cutters. . 293; 175 Types and Uses of Milling Cutters. 296 17.6 Methods of Milling 304 17.7 Holding and Driving 306 17.8 Milling Cutting Speeds and Feeds. £308 17.9 Cutting Fluids -310 17.10 Milling Work-holding Attachments Chapter 18, Milling Machine Operations 310 IT 181 317 18.2 oe BIT 18.3 ..317 18.4 Milling Machine Care 185 Horizontal Maing Machine Operations 18.6 Slitting...... 187 Slotting bx 188 Drilling and Boring on a Horizontal Mailing Machine. 11111339 18.9 Cutting a Spur Gear. ..... 18.10 Cutting a Bevel Gear. 18.11 Precautions When Operating a Ming Machine . 18.12 Industrial Applications . 2349 Chapter 19. Precision Grinding . beeen eee 19.1 Types of Surface Grinders... : 19.2 Workholding Devices. 193 Grinding Wheels . 194 Cutting Fluids (Coolants) 195 Grinding Applications 196 Grinding Problems . 19.7 Grinding Safety . 198 Universal Tool and Cutter Grinder - 199 Tool and Cutter Grinding Wheels 19.10 Cylindrical Grinding. : 19.11 Internal Grinding. 19.12 Centerless Grinding, 19.13 Form Grinding. . 19.14 Other Grinding Techniques - Chapter 20. Band Mac! 201 Band Machining Advantages 20.2 Band Blade Selection . 203 Welding Blades 20.4 Band Machine Prepai . 205 Band Machining Operations. 20.6 Band Machine Power Feed . . 207 Other Band Machining Applications 208 Troubleshooting Band Machines ... 20.9 Band Machining Safety...Chapter 21. Computer Numerical Control......399 21.1 Computer-aided Machining Technology. : e399 21.2 Positioning with Numerical Control . °. 401 21.3 NC Movement Systems. .. 404 214 Programming NC Machines. 408 215 Computer Languages . . 412 21.6 Adaptive Control. +413 21.7 NCand the Future 2413 21.8 Advantages and Disadvantages of NC 415 Chapter 22. Automated Manufacturing......... 423 22.1 Flexible Manufacturing System . . : 4 22.2, Robotics . 424 223 Safety In Automated Manufacturing 428 224 Rapid Prototyping Techniques ..... 4B 225. The Future of Automated Manufacturing. 1433 Chapter 23. Quality Control .. 23.1. The History of Quality Control .... 23.2 Classifications of Quality Control .. 233 Nondestructive Testing Techniques BA Other Quality Control Techniques. Chapter 24. Metal Characteristics . 24.1 Classifying Metals . 24.2 Ferrous Metals . ... 243 Nonferrous Metals. 244 Copper-based Alloys. 245 High-temperature Metals 24.6. Rare Metals..........+ Chapter 25. Heat Treatment of Metals ..... 25.1 Heat-treatable Metals . wae ® 25.2. Types of Heat Treatment. 25.3 Heat Treatment of Other Metals. 254 Heat-treating Equipment 255 Hardening Carbon Steel . 25.6 Tempering Carbon Steel . 25.7 Case Hardening Low-carbon Steel” 25.8 Hardness Testing . . . 259 Heat-treating Safety. Chapter 26. Metal Finishing 26.1 Quality of Machined Surfaces. .. 26.2 Other Metal Finishing Techniques . Chapter 27. Electromachining Processes .. 27.1 Electrical Discharge Machining (EDM) . . 27.2 Electrical Discharge Wire Cutting (EDWO). 27.3. Electrochemical Machining (ECM). 492Chapter 28. Nontraditional Machining Techniques ... 28.1 Chemical Machining . we 282 Hydrodynamic Machining (HDM) . 28.3 Ultrasonic Machining . . 284 Electron Beam Machining (EBM 285 Laser Beam Machining .... Chapter 29. Other Processes... 29.1 Machining Plastics. . 29.2 Chipless Machining 29.3 Powder Metallurgy 294 High-energy rate Forming (IERF) 29.5 Cryogenic Applications ...... Chapter 30. Occupations in Machining Technology. te eeee ee ee BAT 30.1. Machining Job Cat “ 302 Preparing aa Jon Machising Tashi wicisesercee BOS 30.3 How toGetajob....... soos Reference Section . . Glossary of Technical Terms ............46.+.+.593 Index coe cece cece eee e eter ete nee eee ne ONSLEARNING OBJECTIVES After studying this chapter, you will be able to: IMPORTANT TERMS A study of technology will show that industry has progressed from the time when everything was made by hand to the present fully automated man- ufacturing of products. Machine tools have played an essential role in all technological advances. ‘Without machine tools, Figure 1-1, there would be no airplanes, automobiles, television sets, or computers. Many of the other industrial, medical, recreational, and domestic products we take for granted would not have been developed. For exam- ple, if machine tools were not available to manufac- fure tractors and farming implements, farmers might still be plowing with oxen and hand-forged plowshares. It is difficult to name a product that does not require, either directly or indirectly, the use of a machine tool somewhere in its manufacture. Today, Chapter l tion to hnology Figure 1-1. Machine tools have made it possible to manufac ture parts with the precision and speed necessary for low-cost ‘mass production. Without machine tools, most products on the ‘market today would not be available or affordable. (Courtesy of SURFCAM by Surfware) no country can hope to compete successfully in a global economy without making use of the most advanced machine tools. ‘There is one very important point that must be emphasized concerning modem manufacturing technology. The high-paying skilled jobs in manu- facturing, such as tool-and-die making and preci- sion machining, require aptitudes comparable to those of college graduates. Jobs that require few or no skills, have almost disappeared. me1.1 THE EVOLUTION OF MACHINE TOOLS Machine tools are the class of machines which, taken as a group, can reproduce themselves (manu- facture other machine tools). There are many varia- tions of each type of machine tool, and they are available in many sizes. Tools range from those small enough to fit on a bench top to machines weighing several hundred tons, The evolution of machine tools is somewhat akin to the old question, “Which came first, the chicken or the egg?” You could also ask, “How could there be machine tools when there were no machine tools to make them?” 1.1.1 Early Machine Tools The first machine tools, the bow lathe and bow Grill, were hand-made. They have been dated back to about 1200 BC. Until the end of the 17th Century, the lathe could only be used to turn softer materials, such as wood, ivory, or at most, soft metals like lead ‘or copper. All of them were human-powered, Eventually, the bow lathe with its reciprocating (back-and-forth) motion gave way to treadle power, which made possible work rotation that was contin- uous in one direction. Later, machines were pow- ered by a “great wheel” tumed by flowing water or Casting being machined by a person or animal walking on a treadmill. Power was transmitted from the wheel to one or more machines by a belt and pulley sy When inventor James Watt first experimented with his steam engine, the need for perfectly bored cylinders soon became apparent. This brought about the development of the first irue machine tool. It was a form of the lathe and was called a “boring mill,” Figure 1-2. The water-powered tool was developed in 1774 by Englishman John Wilkinson. This machine was capable of turning a cylinder 36” in diameter to an accuracy of a “thin-worn shilling”(an English coin). However, operation of the boring mill, like all metal cutting lathes at the time, was hampered by the lack of tool control. The “mechanic” (the first machinist) had to unbolt and reposition the cutting tool after each cut. About 1800, the first lathe capable of cutting accurate screw threads was designed and construct ed by Henry Maudslay, an English master mechanic and machine toolmaker. As shown in Figure 1-3, a hand-made screw thread was geared to the spindle and moved a cutting tool along the work, Maudslay also devised a slide rest and fitted it to his lathe. It allowed the cutting too! to be accu- rately repositioned after each cut. Maudslay’s lathe is considered the “granddaddy” of all modem chip- making machine tools. Figure 1-2. The first true machine tool's thought to be the boring mill invented by John Wilkinson in 1774. it enabled James Watt to ‘complete the first successful steam engine. The boring bar was sigily supporied at both ends, and was rotated by waterpower. It could bore a 96” diameter cylinder to an accuracy of less than 1/16”. (DOALL Co.)Chapter |___An Introduction to Machining Technology Figure 1-3. Henry Maudslay’s screw-cutting lathe. This ‘machine tool, consiructed on a heavy frame, combined a mas- tor lead screw and a movable slide rest. The lead screw had to be changed when a different thread pitch was required. (DoALL Co.) In retrospect, the Industrial Revolution could not have taken place if there had not been a cheap, convenient source of power: the steam engine. Until the advent of the steam engine, industry had to locate near sources of water power. This was often some distance from raw materials and workers. With cheap power, industry could locate where workers were plentiful and where the products they produced were needed. The steam engine, in turn, would not have been possible without machine tools. Until the boring mill and lathe were devel- oped to the point where metal could be machined with some degree of accuracy, there could be no steam engine. ‘The milling machine was the next important development in machine tools. It also evolved from the lathe. In 1820, Eli Whitney, an American inven- tor and manufacturer, devised a system to mass pro- duce muskets (guns). Whitney began using a milling machine, Figure 1-4, to make interchange- able musket parts. Until then, muskets were made individually by hand, so parts from one musket would not fit in another. Whitney's milling machine even had power feed, but it had one defect. There was no provision to raise the worktable. The part had to be raised by shimming after each cut. Since each machine was used to produce the same part again and again, this shortcoming was not a great problem. It wasn’t too much later that this problem was corrected. Figure 1-4. Ono of he frst practical miling machines manutac- tured in America. Eli Whitney used it and similar machines to ‘mass-produce musket parts that were interchangeable. (DoALL Co.) Whitney had another problem, however. His ideas were used in several armories producing gun parts. There was no standard of measurement at that time, so parts made in one armory were not interchangeable with parts in another armory. It was not until the mid-1860s that the United States adopted a standard measuring system. By 1875, basic machine tools such as the lathe, the milling machine, and the drill press, Figure 1-5, were capable of attaining accuracies of one one- thousandth of an inch. America was well on its way to becoming the greatest industrial nation in the world, 1.1.2 Power Sources ‘As machine tools were improved, so was the way they were powered. At first, the changes were very slow, taking hundreds of years. The great changes have come only in the last 150 years or so. '» Hand power. The bow lathe and bow drill are examples. Direction of rotation changed at each stroke of the bow. + Foot power. A treadle or a treadmill made pos- sible continuous rotation of the work in one direction. » Animal power, Treadmills were used to power early devices for boring cannon barrels. Human foot power was not suificiently strong for this work.Machining Fundamentals Figure 1-5. tustrations of Pratt & Whitngy machine tools from an 1878 advertisement. Bult from heavy iron castings, the machines were driven by overhead putleys and belting. A central steam engine or large electric motor powered the overhead pulleys in facto- tos until the 19203. © Water power. Not always dependable as a power source, because of lack of water during, ‘dry seasons. ‘© Steam power. The first real source of depend able power. A centrally located steam engine turned shafts and overhead pullevs that were belted to the individual machines. © Central electrical power. Large electric motors simply replaced the steam engines. Power transmission to the machines did not change. © Individual electrical power. Motors were built into the individual machine tools. Overhead belting was eliminated. 1,2 BASIC MACHINE TOOL OPERATION Almost all machine tools have evolved from the lathe, Figure 1-6. This machine tool performs one of the most important machining operations. It oper- ates on the principle of work being rotated against the edge of a cutting tool, Figure 1-7. Many other operations—drilling, boring, threadcutting, milling, and grinding—can also be performed on a lathe. ‘The most advanced version of the lathe is the CNC turning center, Figure 1-8. See Chapters 13-15 for basic lathe operations, and Chapters 21 and 22 for automated machining. Figure 1-6. & modem lathe using digital technology to perform ‘operations such as maintaining a constant surlace speed, auto- ‘matic threading cycle, automatic radius cutting, and taper turn- ing. Note tho safety shield that moves withthe carriage. Except ‘those tools that perform nontraditianal machining operations, all ‘machine tools have evolved from the lathe. (Harrison Rem Sales, inc.) 1.2.1 Deill Press A drill press, Figure 1-9, rotates a cutting tool (drill) against the material with sufficient pressureChapter 1 An Introduction to Machining’ Technology Figure 1-7. The lathe operates on the principle of the work being rotated against the edge ofa cutting tool. Figure 1-8 Slant bod CNG lathe with hydraulic chucking land an electronically indexed 12 station turet. (Clausing industrial, Inc.) to cause the tool to penetrate the material. It i primarily used for cutting round holes. See Figure 1-10, Drill presses are available in many ver- sions. Some are designed to machine holes as small as 0.0016” (0.04 mm) in diameter. See Chapter 10. 1.2.2 Grinding Machines Grinding, Figure 1-11, is an operation that removes metal by rotating a grinding wheel or abra- sive belt against the work. The process falls into two basic categories: © Offhand grinding. Work that does not require great accuracy is hand-held and manipulated until ground to the desired shape. See Chapter 11. Figure 1-9. A typical 20” variable-speed gear head dil press with power feed. Itcan dril holes up fo 1 1/2" in alameter in cast iron, (Wills Machinery and Tools Corp.) 4 Figure 1-10. A dill press operates by rotating a cutting tool (Ail) against the material with sufficient pressure to cause the too! to penetrate the materiel,Figure 1-11. Grinding is a cutting operation, lke turing, driting, :iling, or sawing. However, instead ofthe one, two. or mutipio- ‘edge cutting tools used in other applications, grinding employs an abrasive too! composed of thousands of cutting edges. © Precision grinding. Only a small amount of material is removed with each pass of the grinding wheel, so that a smooth, accurate surface is generated. Precision grinding is a finishing operation. See Chapter 19. 1.2.3 Band Machines Band machining, Figure 1-12, is a widely employed technique that makes use of a continuous saw blade. Chip removal is rapid and accuracy can Figure 1-12. Band machining makes use of a continuous saw blade, with each tooth functioning as a precision cutting tool. Machining Fundamentals be held to close tolerances, eliminating or minimiz- ing many secondary machining operations. See Chapter 20. 1.2.4 Millling Machine A milling machine rotates a multitoothed cutter into the work, Figure 1-13, A wide variety of cutting operations can be performed on milling machines. See Chapters 17 and 18. A ‘Work travet End mil rotation Figure 1-13. Miling removes material by rotating a mutttoothed ‘cutter into the work. A—With peripheral miling, the surface being machined is parallel to periphery of the cutter. B—End ‘ills have cutting edges on the circumference and the end.Chapeer | 1.2.5 Broaching Machines Broaching machines are designed to push or pull a multitoothed cutter across the work, Figure 1- 14. Each tooth of the broach (cutting tool) removes only a small amount of the material being machined. An Introduction to Machining Technotagy Too! travel Figure 1-14, A broach is a multitoothed cutting too! that moves ‘against the work. Each tooth removes only a small portion of the ‘material being machined. The cuiting operation may be on a vertical or horizontal plane. 1.3 NONTRADITIONAL MACHINING PROCESSES There are a number of machining operations that have not evolved from the lathe. They are clas- sified as nontraditional machining processes. These include: * Electrical discharge machining (EDM). An advanced machining process that uses a fine, accurately controlled electrical spark to erode metal. * Electrochemical machining (ECM). A method of material removal that shapes a workpiece by removing electrons from its surface atoms. In effect, ECM is exactly the opposite of electroplating. © Chemical milling. A process in which chemi- cals are employed to etch away selected por- tions of metal. + Chemical blanking. A material removal method in which chemicals are employed to produce small, intricate, ultrathin parts by etching away unwanted material. + Hydrodynamic machining (HDM). A comput- er-controlled technique that uses a 55,000 psi water jet to cut complex shapes with mini- mum waste. The work can be accomplished with or without abrasives added to the jet. + Ultrasonic machining. A method that uses ultrasonic sound waves and an abrasive slur ry to remove metal. * Electron beam machining (EBM). A thermo- electric process that focuses a high-speed ‘beam of electrons on the workpiece. The heat that is generated vaporizes the metal. * Laser machining. The laser produces an intense beam of light that can be focused onto ‘an area only a few microns in diameter. It is ‘useful for cutting and drilling, * Hexapods. CNC has made possible uncon- ventional machine tools that use new work- positioning and tool-positioning concepts. See Figure 1-15. These tools, already available to industry, utilize the same movement prin- ciples developed for the flight simulators that train aircraft pilots. They offer basic advan- tages in stiffness, accuracy, speed, dexterity, and scaling (making larger or smaller ver- sions of the same part). 1.4 AUTOMATING THE MACHINING PROCESS In the late 1940s, the United States Air Force was searching for ways to increase production on com- plex parts for the new jet aircraft and missiles then going into production. ‘The Parsons Corporation, a manufacturer of air- craft parts, had developed a two-axis technique for ‘generating data to check helicopter blade airfoil pat- terns. This system used punched-card tabulating ‘equipment. To determine the accuracy of the data, a pattern was mounted on a Bridgeport milling machine. With a dial indicator in place, the X and Y points were called out to a machinist operating the machine’s X-axis handwheel and another machinist ‘who controlled the Y-axis handwheel. With enough reference points established, the generated data proved accurate to 0.0015” (0.038 mm),