11: Machine Tools

Machine tool, any stationary power-driven machine that is used to shape or form parts made of metal or other materials. The shaping is accomplished in four general ways: (1) by cutting excess material in the form of chips from the part; (2) by shearing the material; (3) by squeezing metallic parts to the desired shape.

Machine tools that form parts by removing metal chips from a workpiece include lathes, shapers and planers, drilling machines, milling machines, grinders, and power saws. The cold forming of metal parts, such as cooking utensils, automobile bodies, and similar items, is done on punch presses, while the hot forming of white-hot blanks into appropriately shaped dies is done on forging presses.

Before the Industrial Revolution of the 18th century, hand tools were used to cut and shape materials for the production of goods such as cooking utensils, wagons, ships, furniture, and other products. After the advent of the steam engine, material goods were produced by power-driven machines that could only be manufactured by machine tools. Machine tools (capable of producing dimensionally accurate parts in large quantities) and jigs and fixtures (for holding the work and guiding the tool) were the indispensable innovations that made mass production and interchangeable parts realities in the 19th century.

The earliest steam engines suffered from the imprecision of early machine tools, and the large cast cylinders of the engines often were bored inaccurately by machines powered by waterwheels and originally designed to bore cannon. Within 50 years of the first steam engines, the basic machine tools, with all the fundamental features required for machining heavy metal parts, were designed and developed.

In 1775 John Wilkinson of England built a precision machine for boring engine cylinders (see right). In 1797 Henry Maudslay, also of England and one of the great inventive geniuses of his day, designed and built a screw-cutting engine lathe (see below). The outstanding feature of Maudslay’s lathe was a lead screw for driving the carriage. Geared to the spindle of the lathe, the lead screw advanced the tool at a constant rate of speed and guaranteed accurate screw threads. By 1800 Maudslay had equipped his lathe with 28 change gears that cut threads of various pitches by controlling the ratio of the lead-screw speed to the spindle speed.

Britain tried to keep its lead in machine-tool development by prohibiting exports, but the attempt was foredoomed by industrial development elsewhere. British tools were exported to continental Europe and to the United States despite the prohibition, and new tools were developed outside Britain. Notable among these was the milling machine invented by Eli Whitney, produced in the United States in 1818, and used by Simeon North to manufacture firearms (below right). The first fully universal milling machine was built in 1862 by J.R. Brown of the United States and was used to cut helical flutes in twist drills (above left). The turret lathe (above middle), also developed in the United States in the middle of the 19th century, was fully automatic in some operations, such as making screws, and it presaged the momentous developments of the 20th century. Various gear-cutting machines reached their full development in 1896 when F.W. Fellows, an American, designed a gear shaper (left) that could rapidly turn out almost any type of gear. More contemporary developments in machine tools include electrification and computer control. In the 1900’s electrification was introduced in to machine tools, further increasing their flexibility and efficiency. Some machine tools of this period had complex gears and levers to fully automate the machine tool process.