Figure 33 (pi. T3) shows a number of hand-turning tools for turning hard-wood, ivory, and brass. Number r is a "milling" tool for impressing a circumferential ornamental line on work previously finished. Numbers 2 and 3 are chasers for cutting fine screw-threads internally and externally respectively. Numbers 4 and 5 are bent "inside" tools; number 6 is a flat tool for outside work; number 9 a " point " and number io a "round point" tool; number II is a square graver; number 12 is for "cutting off" and numbers 13 and 14 are for general turning.
Referring to Plate 19 (jigs. 5, 6), number i is known as a " left-side " tool; number 2 is the same style, made " right hand." Numbers 3 and 4 are the same types, "bent" for working at an obtuse angle. Number 5 is a heavy "diamond-point" tool for cast iron; numbers 6 and 7 are right-hand and left-hand diamond points for steel and wrought iron. Number S shows a " half-diamond point " and number 9 a " round-nose." Number io is a "water-finishing" tool, which takes off a very fine, wide turning. Num ber it is for cutting off pieces in the lathe; number 12 for roughing stock; number 13 for cutting external or " male " V-threads, and number 14 the same as number bent. Number 15 is for turning a hollow cylinder; number 16 for cutting an internal or " female " screw-thread. All the foregoing are used in a slide-rest.
Of Figures 4 to S (pi. 2o), Figures 5 and 6 are ordinary turning-tools for metal and Figure 4 one for wood, while Figures 7 and S are examples of a tool whose cutting-edge consists of a three-cornered bar or piece of steel set in an iron stock. This allows of very economical use of the steel and dispenses with the otherwise unavoidable forging of the entire tool.
in which the guidance of the tool is effected by mechanism instead of by hand are called "slide-rest'' lathes, a simple form being shown in Figure to (pi. 2o). The mandrel carries a stepped or cone pulley with various diameters corresponding to those of a similar stepped pulley on the counter-shaft, the revolving motion of the latter being transmitted to the former by a belt. The tool is firmly secured to a rest, which receives a motion parallel to the rotating axis by a lead screw in the interior of the bed, the nut and the screw being carried by the slide-rest. The rotation of this lead-screw is derived from that of the mandrel by belt- and wheel-gearing. This arrangement is suitable only for producing cylindrical surfaces. Sometimes engine-lathes are provided with contrivances for guiding the tool in other than a straight line—for instance, with a special guide-bar, against which the uppermost cross-slide is constantly pressed by a weight (curved slide-rest; j51. 20, fig. 13).
lathe shown in Figure i (j51. 2 t) differs from the preceding in two particulars. Besides the mandrel the head-stock contains au auxiliary appliance placed parallel to the mandrel, so that the former can be connected with the latter by a pair of wheels, through which the motion transmitted to the step-pulleys can be communicated in a retarded velocity to the mandrel itself. As the step-pulleys can be directly con nected with the mandrel, it is possible, with the four varying diameters of the step-pulley, to give the work eight different velocities, and thus to obtain the most advantageous peripheral speeds according to the different materials to be worked. This class of appliances is described in very full detail under the head of screw-cutting lathes (p. ioS).
Another peculiarity of the lathe (jig. 1) is the simultaneous action upon both sides of the work of two turning-tools, which, it is claimed, not only double the capacity of the lathe, but also, by the action of the tool, prevent the work from springing. To hold these two tools the car riage has two special cross-slide rests, each allowing its tool to be traversed in two directions at right angles to each other. The details of such slides are shown in Figures it and 12 (p1. zo).
Gad-bed give engine-lathes the widest possible range of work they are frequently provided with a gap-bed (jig. 14). Directly alongside the head-stock and beneath the head of the mandrel—which must be provided with suitable contrivances for securing the work— the bed-plate is depressed within a certain length, to allow turning work, if not too lon,g, with a radius greater than the height of the centre from the general bed-level. The advantage of this kind of lathe lies in the fact that work is most frequently either long and thin or short and thick. This lathe forms the transition to those exclusively intended for spher ical or flat work of a larger diameter, the so-called "face-plate" lathes (pt. 21, //AY'S. 2, 3), in which the work is fastened to a large cast-iron plate (face-plate) provided with hollows and T-shaped slots and screwed upon the head of the spindle. The tail-stock or sliding poppet either is placed, together with the slide-rest, upon a special bed (fig. 3)—which is, however, connected with the head-stock by a foundation-plate—or is entirely omitted (fig. 2), in which case only a special framing for the slide-rest is required. Such lathes are very convenient for turning large pulleys, gear-wheels, tur bines, etc.