Machine Tools

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.

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.