Machine Tools

I

Introduction

Machine Tools, stationary power-driven machines used to shape or form solid materials, especially metals. The shaping is accomplished by removing material from a workpiece or by pressing it into the desired shape. Machine tools form the basis of modern industry and are used either directly or indirectly in the manufacture of machine and tool parts.

Machine tools may be classified under three main categories: conventional chip-making machine tools; presses; and unconventional machine tools. Conventional chip-making tools shape the workpiece by cutting away the unwanted portion in the form of chips. Presses employ a number of different shaping processes, including shearing, pressing, or drawing (elongating). Unconventional machine tools employ light, electrical, chemical, and sonic energy; superheated gases; and high-energy particle beams to shape the exotic materials and alloys that have been developed to meet the needs of modern technology.

II

History

Modern machine tools date from about 1775, when the English inventor John Wilkinson constructed a horizontal boring machine for producing internal cylindrical surfaces. In about 1794 Henry Maudslay developed the first engine lathe. Later, Joseph Whitworth speeded the wider use of Wilkinson’s and Maudslay’s machine tools by developing, in 1830, measuring instruments accurate to a millionth of an inch. His work was of great value because precise methods of measurement were necessary for the subsequent mass production of articles having interchangeable parts.

The earliest attempts to manufacture interchangeable parts occurred almost simultaneously in Europe and the United States. These efforts relied on the use of so-called filing jigs, with which parts could be hand-filed to substantially identical dimensions. The first true mass-production system was created by the American inventor Eli Whitney, who in 1798 obtained a government contract to produce 10,000 army muskets, all with interchangeable parts.

During the 19th century, such standard machine tools as lathes, shapers, planers, grinders, saws, and milling, drilling, and boring machines reached a fairly high degree of precision, and their use became widespread in the industrializing nations. During the early part of the 20th century, machine tools were enlarged and made even more accurate. After 1920 they became more specialized in their applications. From about 1930 to 1950 more powerful and rigid machine tools were built to utilize effectively the greatly improved cutting materials that had become available. These specialized machine tools made it possible to manufacture standardized products very economically, using relatively unskilled labour. The machines lacked flexibility, however, and they were not adaptable to a variety of products or to variations in manufacturing standards. As a result, in the past three decades engineers have developed highly versatile and accurate machine tools that have been adapted to computer control, making possible the economical manufacture of products of complex design. Such tools are now widely used.

III

Conventional Machine Tools

Among the basic machine tools are the lathe, the shaper, the planer, and the milling machine. Auxiliary to these are drilling and boring machines, grinders, saws, and various metal-forming machines.

A

Lathe

A lathe, the oldest and most common type of turning machine, holds and rotates metal or wood while a cutting tool shapes the material. The tool may be moved parallel to or across the direction of rotation to form parts that have a cylindrical or conical shape, or to cut threads. With special attachments, a lathe may also be used to produce flat surfaces, as a milling machine does, or it may drill or bore holes in the workpiece.