and producing articles of circular cross sections machines such as are represented on Plate 20 (figs. I, 2) are indis pensable auxiliaries. The material to be worked is revolved, generally, around a horizontal axis, while a turning-tool, supported in a suitable rest and made to aot upon its periphery, detaches material in the form of turn ings or shavings. As each point of a rotating body describes a circle, all cross-sections of the material at right angles to its axis must become circles, provided the distance of the tool from the rotating axis be not changed during the rotation. By giving the tool, during the rotation of the work, a motion parallel to the axis, there will result a helical cut whose separate convolutions, lying closely together, form a cylindrical surface, and by changing the course of the tool conical, straight, spherical, or other surfaces may be produced.
—The oldest and simplest arrangement for turning is the " turn-bench " Jig. i), at present used only for shaping very small arti cles, such as ebony, bone, or ivory chessmen, or the cylindrical parts of the works of clocks and watches. The piece to be shaped is secured between two conical steel points held in two poppets, one of which is fixed to a bar, which may be secured in a vise, while the other can be shifted upon this bar according to the length of the piece to be worked. Upon the work to be shaped is placed a small pulley, around which is passed the cord of a drill-bow. By drawing the bow to and fro with one hand the work to be shaped is rotated first in one direction and then in the opposite direction, while the removal of the turnings is effected by a tool held in the other hand and supported by a rest on a Trail which extends from one poppet to the other. Formerly turn-benches in which the work was rotated by a treadle were much used. A cord fastened to the treadle passed two or three times around the work and was attached to the end of an elastic pole or lath (hence the term " lathe ") fixed above the head of the turner.
the turning-tool can act upon the work only during the rotation of the latter toward the tool, half the time is lost by the use of the turn-bench, and turning contrivances at the present time are exclusively used for giving an uninterrupted rotation in one direction. The principal types of these contrivances (lathes) are represented on Plates 20 to 23.
the ordinary foot-lathe (pl. 20, jig. 2) a driving-shaft, resting in the lower portion of the frame and connected by a cord with a mandrel in the upper portion, toward the left hand of the turner, is rotated by a treadle. The piece to be shaped is so attached to this
mandrel as to rotate with it. Long pieces of work are supported on the centre of the outer end by a pin fixed in the so-called "sliding poppet," whose distance from the head-stock or mandrel-stock can be varied according to the length of the piece to be shaped. The tool is held by both hands, with a " rest " as a support, and thus forms a lever upon whose short arm falls the resistance of the material, while the hands of the turner act upon the long arm. These foot-lathes are about the same for wood-working as for metal-working, the principal differences being that for wood the rotation speed is higher, and the method of attachment to the mandrel is usually by points projecting from the live spindle instead of by bolts, or by projections in the face-plate of the lathe, or by "chucks" which grasp the periphery of the object held.
shaped tools used with such lathes are shown. in Figure 3, the first six serving for "turning" proper and the last two for cutting screw or circular threads in previously formed cylin drical or conical surfaces. Figure 33 (p/. 13) shows a number of hand turning tools for turning hard-woods, ivory, and brass. (See p. 105.) and wood-turner no longer uses calipers to gauge the depth of cut and regulate the outline or profile of his work, nor is he limited to the production of shapes which are circular in every cross-section, for he can employ lathes which, while turning out objects that are thus circular in every transverse cut, insure perfect profile and size; and he may also turn out such irregularly shaped objects as axe helves, gun-stocks, etc., the machine not only regulating the depth of cut and the profile, but also producing the desired amount of eccentricity and non-circularity of cross-sections. But the gauge- and copying-lathe of to-day are considerably in advance of those of a decade ago (p7. 20, 9), and America, which originated these types, still leads the world therein. In gauge-lathes a desirable feature is a small guard upon the follower, which regulates the thickness of the shaving taken by the finishing-knife and prevents the knives from digging into the stick. Another good ele meat in sonic of these machines is that the head- and tail-blocks are milled out to fit the ways and have a bearing over their full extent, so that the blocks can be set their entire length over the ends of the bed and turn longer than the regulation length. Shorter blocks than the maximum can be turned by moving the tail-block up toward the head.