TURNING, the art of shaping wood, metal, ivcry, or other hard substances into forms having a curved (generally circular or oval) transverse section, and also of engrav inc figures composed of curved lines upon a smooth surface, by means of a machine called a turning-lathe. Thus art is of great importance and extensive application in mechanics, the most delicate articles of luxury and ornament, equally with the most ponderous machinery, being produced by it. The art of turning; dates from a very early period, and Theodorus of Samos (about 560 B. C.) is named by Pliny as its inventor; but long before this period, the potter's wheel (KC POTTERY) the earliest and simplest form of turning-machine, was in general use, as is evidenced by numerous references in Holy Writ. The immense variety of work performed by turning-machines necessitates great variations in their construction; but their mode of operation is always the same, and consists in fixing the work in position by two pivots or otherwise, causing it to revolve freely round an axis of revolution, of which the two pivotS are the poles, and holding a chisel or other so as to meet it during its re rohnion, taking care that the cutting-tool be held firmly and steadily, and moved about to different parts of the work till the required shape be obtained. Lathes are divided, with respect to the mode of setting them in motion, into pole-lathes, foot-lathes, hand-wheel lathes, and power-lathes, with respect to the species of work they have to perform, into ern/LT-lathes, which form the outside surface. and spindle, mandrel, or chuck lathes, which perform hollow or inside work, though this distinction is for the most part useless, as all lathes of good construction are now fitted for both kinds of work. Bed-lathes are those used by turners in wood, and bar-lathes for the best sort of metal-work; and the small metal center-lathe employed by watchmakers is known as a turn-bench.
The primitive and most simple form of lathe for wood-cutting is the pole lathe. It consists of two planks or beams placed horizontally side by side with a narrow space between them, which, being firmly supported at a convenient height, constitute the bed; of two uprights or puppets rising from the bed, one of them stationary at the left end, and the other sliding along over the slit between the beams, and capable of being fast ened at any required point by a projecting tenon and wedge beneath; of a treadle below and parallel to the bed; and of an elastic pole or lath (whence some derive the name lathe) fixed to the ceiling above. This form of lathe is well adapted for turning long
thin cylinders of wood, the piece to be turned being held fast at each end by the (nnical iron or steel point projecting from the inner face of each puppet. Motion is communi cated to the work by a cord which is fastened to the lath overhead, wound twice or thrice round the work, and then attached to the treadle below. When the workman presses his foot ou the treadle, the work commences to revolve rapidly, unwinding the cord toward the treadle, and it up on the side next the pole, causing the latter to bend considerably. During this period the workman has been holding his cutting instrument to the work; but after the treadle has been quite pressed down, he removes his foot, and the reaction of the bent pole causes the work to revolve in an opposite direc tion, till the pole has straightened itself; and during this latter revolution no cutting is (loin:. When the whole piece is to be turned, the cord must be moved from on ished to a finished part of the work. For the pole, an elastic steel bow and string are substituted when the work is light, or fine, the cord being attached to the middle of the string, and the bow fastened to the ceiling by its center. The advantage of the lathe is that it never acquires an impetus hi the direction of the cutting motion, for whenever the pressure on the treadle is removed the reaction of the pole takes effect; hut the great waste of time during the straightening of the pole and rising of the treadle has caused the abandonment of this machine for the foot-lathe. The foot-lathe, the most common and generally useful form of lathe, differs from the former iu having is or in place of the left-hand stationary puppet. This bead-stock, 1III (lig. 1), consists of two supports or puppets firmly connected at their base, and fastened at right angles to the bed by means of the screws A,A; the outer pet is pierced for the screw S; and the inner is supplied with a steel collar,within which the mandrel, M, which carries the ,,,,, ....11,..— 1.) 'Mtn 1.•ft nr,r1 of 0, J. 4.1.0. J.