The lathe is the parent of all machine tools, and some of its elements are curiously traceable in many kinds of machines, including fresh types not known a quarter of a century ago.
Machines derived from the lathe model include the boring, drilling, milling, sawing and grinding machines; the planing ma chine was a new departure rendered necessary by the introduction of flat surfaces in steam-engines and machines. These at first were made slowly and laboriously with hammer and chisel and file, but on the planer they were readily and accurately surfaced by passing under a tool. Then for smaller articles the shaper was invented, the object remaining fixed on a table while the tool was recipro cated by a ram above; the slotting-machine is practically a vertical type of shaper, the tool going up and down and cutting along edges according to how the table feeds the work; the broaching machine, a recent type, effects its cut in one instead of many strokes (as in the preceding machines), the broach being a long tool furnished with teeth increasing in cutting depth, so that a hole or slot is cut a trifle deeper by each tooth in the traverse of the broach through the hole. This method is quick and highly accurate, besides being suited for shapes that are awkward to plane, shape, slot or mill.
All drilling and boring was at first—and much of it still is—effected in the lathe; but the upright drilling-machine, in which the object to be treated can be held in a more convenient position while the drill descends on it, was soon developed. Horizontal boring Machines, too, were built with slight differences from the lathe ; these gradually extending to alterations which radically changed the appearance, though the revolving spindle remained, and the essential differ ences are greater adjustability to suit different sizes of work and improved means for holding the latter. The speed range of the spindle of a drilling or a boring machine is often more extensive than that of a lathe, the light sensitive drills for small holes run ning up to 12,000 revolutions or more per minute, with means for going at slower speeds for larger drills or extra hard metal; such a speed is necessary to secure the full advantage of the high-speed steel drills. A great enhancement of output is obtained in automo
bile factories, engine works, valve and fitting factories and others by using multi-spindle machines. Instead of putting one drill through the metal at a pass of the spindle, the latter is duplicated, or multiplied into of ten scores of spindles, each holding a drill, so that all the holes wanted in the face of the work are drilled simultaneously.
Milling was originally also performed in the lathe, the rotating cutter being driven by the spindle while the piece of metal was fed under it by the slide-rest ; and from th at principle dozens of different kinds of milling-machines utilizing cutters of various shapes that can finish flat surfaces, curves, slots and every conceivable shape required in metal construction from the tiniest to the most massive, have been evolved. Wood is also milled on machines of a somewhat different type, and forms in either wood or metal which would be slow and tedious to pro duce on certain other machine-tools and difficult by hand methods alone, can be milled in a brief time with great accuracy. As in most instances the milling-cutter imparts its shape or part shape upon the metal, the intricate outlines are as easy to cut as the plain flat ones; hence a cutter or set of cutters mounted together will mill flats, bevels, curves and slots along a casting or forging all in perfect relationship and turn out hundreds or thousands of pieces alike. As in drilling, two or more spindles may be fitted on a machine, and the work be milled on each flank, or at top and sides, or underneath. Cylinder blocks, crank-cases and various parts of engines and machines are bolted on a long table to feed past such cutters, so that when the table has completed its feed from 6 to 20 units have received treatment. The quantity will be greatly increased if a double row is laid down the table, the cutters milling on one side only of each piece. Mass production in the motor-car and other factories has extended so much that even the halting of a machine for the purpose of removing milled units and putting on others to be done has been partly abolished.