machine tool

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Machine tools are devices used to build parts of machines; but usually the concept is interpreted more narrowly, denoting tools that cut or drill, press or shear, or otherwise shape hardened materials into specific forms. Although casting is often one of the most important steps in producing a part, casting per se does not use machine tools. A mold may, however, have been shaped by machine tools. A classic description of how a sculptor works says that the sculptor takes a block of marble and removes everything that does not look like the statue in mind. Most machine tools work the same way, removing metal or ceramic a little at a time until the part the designer had in mind is all that is left.

The first machine tool was among the first machines invented; the bow drill goes back at least to Neolithic times. But the main ancestor of machine tools was not a machine tool itself. The potter's wheel, dating from about 6000 years ago, was originally used to shape soft material only. It cannot count as a machine tool because clay is not hard until after firing. By classical Greek times, however, the potter's wheel had become a part-time machine tool, helping smooth imperfections from fired pottery.

Although records are scarce, that application of the potter's wheel apparently merged imperceptibly into the principal machine tool used even today, the lathe. A lathe is a device for rotating a hard object, originally wood and later mostly metal, so that the object can be shaped by a stationary cutter. We know that early lathes had been developed because we find parts such as chair legs that had clearly been produced by "turning" on a lathe. But it is not until the 15th century, when Leonardo drew a lathe, that we learn anything about the device apart from its products. Leonardo's lathe is thought not to have been an invention, but a then-common type of wood lathe with a treadle and a spring pole.

During the 16th century, the art of lathe making advanced, and the lathe was adapted for making screws. Although early screws were used as fasteners, the application of screws for delicate adjustments was far more important. This use of screw adjustors ensured the accuracy of the machine parts produced. In addition to screw making, various adaptations of lathes throughout the 17th century using cams and patterns enabled the wood lathe to cut complicated figures, not just circles with different radii.

The 18th century began with a metal-cutting lathe built in 1701, but its builder clearly stated that his was not the first such lathe, but one of a very few. By the end of the century, however, metal lathes were much more common. Jacques de Vaucanson was among the first builders of the heavy, industrial lathe, which appeared in France before it did in England. A surviving lathe by Vaucanson was apparently built between 1770 and 1780. The English soon surpassed the French, however. English lathes by Henry Maudslay, built in the early 19th century, set the standard for the time. Maudslay turned out in his shop not only the best lathes of the time, but also the best machine tool manufacturers. Almost all the machine builders of the Industrial Revolution in Britain can trace their heritage directly or indirectly to Maudslay's shop.

Maudslay's reputation and the place of machine tools in industry were both set during a seminal operation at the Portsmouth Naval Yard at the start of the 19th century. Using a system set up by Marc Brunel and Samuel Bentham, the production of pulleys (known to shipbuilders as "blocks") was completely mechanized. Although this operation had been partly mechanized as early as 1780, the new system used a special tool for each step in the operation. The arrangement was copied so extensively in the United States and blended so well with earlier U.S. developments of standardized parts in gun manufacture, that the whole process came to be called the "American system" of manufacture.

The lathe is the basic machine tool. Variations on the lathe, such as boring machines, grinders, milling machines, and planers, all of which use rotary motion to remove unwanted material, leaving the partly or completely finished part, are generally considered separately. These tools, all of which advanced in the mid-19th century, were also essential to the growth of industry. The cannon-boring machine, adapted to making strong cylinders for steam engines, is often cited as a key development.

Standardized parts and mass production are worthless without excellent measurement standards, as early standardizers found, often to their dismay. Concurrent with and necessary to the development of good machine tools was the development of better ways to measure parts. Joseph Whitworth, from Maudslay's shop, was one of the first to recognize this, developing various standards, including the bench micrometer, that improve accuracy from "can't fit a well-worn penny between the parts" early in the 19th century to one ten-thousandth of an inch or better by the middle. Whitworth also introduced plug-and-ring gauges, which led to the first "go-no-go" gauges -- if the part was right it would fit into the larger or "go" gauge but not quite fit in the "no-go" smaller gauge. By the end of the 19th century gauge blocks that could be combined to measure with accuracies of a millionth of an inch were available. These tools were used to measure other tools that were sometimes in turn used to measure other ones; although there was some loss in precision along the way, the tools used in the shop could always be recalibrated as necessary by the experts. As a result, standardized parts produced by machine tools could become fully interchangeable all over the world.

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Lathe is an example of a machine tool

A machine tool is a powered mechanical device, typically used to fabricate metal components of machines by machining, which is the selective removal of metal. The term machine tool is usually reserved for tools that used a power source other than human movement, but they can be powered by people if appropriately set up. Many historians of technology consider that the true machine tools were born when direct human involvement was removed from the shaping or stamping process of the different kinds of tools. The earliest lathe with direct mechanical control of the cutting tool was a screw-cutting lathe dating to about 1483.^[1] This lathe "produced screw threads out of wood and employed a true compound slide rest".

The first machine tools offered for sale (i.e. commercially available) were constructed by one Matthew Murray in England around 1800.^[2]

Contents 1 Overview 2 Examples 3 See also 4 References 5 Bibliography 6 Further reading 7 External links

Overview

Machine tools can be powered from a variety of sources. Human and animal power are options, as is energy captured through the use of waterwheels. However, modern machine tools began to develop only after the development of the steam engine, which led to the Industrial Revolution. Today, most machine tools are powered by electricity.

Machine tools can be operated manually, or under automatic control. Early machines used flywheels to stabilize their motion and had complex systems of gears and levers to control the machine and the piece being worked on. Soon after World War II, the numerical control (NC) machine was developed. NC machines used a series of numbers punched on paper tape or punch cards to control their motion. In the 1960s, computers were added to give even more flexibility to the process. Such machines became known as computerized numerical control (CNC) machines. NC and CNC machines could precisely repeat sequences over and over, and could produce much more complex pieces than even the most skilled tool operators.

Before long, the machines could automatically change the specific cutting and shaping tools that were being used. For example, a drill machine might contain a magazine with a variety of drill bits for producing holes of various sizes. Previously, either machine operators would usually have to manually change the bit or move the work piece to another station to perform these different operations. The next logical step was to combine several different machine tools together, all under computer control. These are known as machining centers, and have dramatically changed the way parts are made.

From the simplest to the most complex, most machine tools are capable of at least partial self-replication, and produce machine parts as their primary function.

Examples

Examples of machine tools are:

• Broaching machine
• Drill press
• Gear shaper
• Hobbing machine
• Hone
• Lathe
• Screw machines
• Milling machine
• Shaper
• Saws
• Planer
• Stewart platform mills
• Grinders

When fabricating or shaping parts, several techniques are used to remove unwanted metal. Among these are:

• Electrical discharge machining
• Grinding
• Multiple edge cutting tools
• Single edge cutting tools

Other techniques are used to add desired material. Devices that fabricate components by selective addition of material are called rapid prototyping machines.

Several regions of the United States became centers for machine tool development between 1800 and 1950, including Philadelphia, Pennsylvania; Cincinnati, Ohio; Rockford, Illinois; Providence, Rhode Island; Springfield, Vermont; Windsor, Vermont; Hartford, Connecticut; and Bridgeport, Connecticut.

See also

• Four slide machine
• Tool bit
• Tool wear
• Clanking Replicator
• Multimachine - an open source machine tool
• James Fox (engineer)
• Machinist calculator
• Metalworking
• Swarf

References

1. ^ Moore, Page 137, figure 213
2. ^ Moore

Bibliography

• Moore, Wayne R. (1970), Foundations of Mechanical Accuracy (1st ed.), Bridgeport, CT, USA: Moore Special Tool Co., LCCN 73-127307 .

Further reading

• Hounshell, David A. (1984), From the American system to mass production, 1800-1932: The development of manufacturing technology in the United States, Baltimore, Maryland, USA: Johns Hopkins University Press, LCCN 83-016269, ISBN 978-0-8018-2975-8 .
• Moltrecht, Karl Hans (1981), Machine Shop Practice (2 vols) (2nd ed.), New York: Industrial Press, LCCN 79-091236, ISBN 978-0831111267 .
• Noble, David F. (1984), Forces of production: a social history of industrial automation, New York: Knopf, LCCN 83-048867, ISBN 978-0-394-51262-4 .
• Roe, Joseph Wickham (1916), English and American Tool Builders, New Haven, Connecticut, USA: Yale University Press, LCCN 16-011753, http://books.google.com/books?id=X-EJAAAAIAAJ&printsec=titlepage . Reprinted by McGraw-Hill, New York and London, 1926 (LCCN 27-024075); and by Lindsay Publications, Inc., Bradley, IL, USA (ISBN 978-0-917914-73-7).
• Rolt, L.T.C. (1965), A Short History of Machine Tools, Cambridge, Massachusetts, USA: MIT Press, LCCN 65-12439 . Co-edition published as Rolt, L.T.C. (1965), Tools for the Job: a Short History of Machine Tools, London: B. T. Batsford, LCCN 65-080822 .
• Woodbury, Robert S. (1972), Studies in the History of Machine Tools, Cambridge, Massachusetts, USA, and London, England: MIT Press, LCCN 72-006354, ISBN 978-0-262-73033-4 . Collection of previously published monographs bound as one volume.

External links

Look up machine tool in Wiktionary, the free dictionary.

• National Institute for Metalworking Skills Standards download page
• U.S. Department of Labor Bureau of Labor Statistics Occupational Outlook Handbook
• American Precision Museum—A museum that preserves historically important machine tools and helps to educate on the history of machine tools
• Canadian Museum of Making

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