Most engineering workshops utilise a number of different machine tools. These are machines which, by varying methods, apply a cutting tool to a piece of metal to alter the shape. The machine tool family includes drills, grinders, milling machines and, by far the most important one, the lathe. With skilled operation the lathe can cut metal to extremely close tolerances, often 0.025 mm.
The work, usually in the form of a metal shaft or bar, is gripped in a set of jaws, called a chuck, which is mounted in the headstock. The chuck is similar in operation to the chuck of a standard DIY electric drill, but usually much larger. The headstock rotates, causing the work to rotate. The work is held at the other end by the tailstock. This is usually done by drilling a small hole in the end of the work, into which is inserted a pointed drift. This is to steady the work as it rotates, often at speeds of up to 2000 revolutions per minute. The cutting tool is mounted on the tool post, which in turn is mounted on a cross slide. This can move at right angles to the work, and is mounted on a saddle which moves along the length of the work, thereby enabling the tool to be positioned anywhere on the piece of work.
The tools are usually made of high speed steel, which is an alloy of chromium, vanadium and tungsten. It is a very hard alloy and is largely unaffected by the high temperatures which occur due to friction whilst cutting. For very high speed the cutting blade is often made from tungsten carbide, which is almost as hard as diamond. To limit the temperatures whilst cutting, a jet of coolant is directed at the cutting edge of the tool. Acting as a lubricant, the coolant is usually white in colour and consists of an emulsion of oil and water.
