The tools used in turning are numerous and varied. For soft wood scarcely any are required besides gouges or round chisels with circular points, to rough out the work, and chisels with an oblique cutting edge, sharpened by being ground and rubbed at a very acute angle on each To give the workman power to prevent the tool dipping or trembling, the tools are set in very long handles, the ends of which very usual and convenient form. T is the place for the tool, which is held down by the screw above : the tools are long square pieces of steel reaching beyond the edges of the plate upon which they are fixed. This plate has two small slips or dovetails screwed on to its under surface and fitting the sides of the plate a, which has a screw along its centre, working in a nut in the upper plate : so that by turning the winch-handle the tool can be moved backward or forward along the plate a, which is about twice the length of the upper or tool plate. Beneath the plate a is a circular piece c, divided by a line into two unequal portions; the upper and thicker portion is screwed to the plate 8 ; the lower is in fact only a circular fillet left upon the plate below : in the centre of the latter is fixed an accurately-turned pin fitting into a corresponding hole in the former, which turns upon it as a centre, and can be set at any required angle to the lower plate (which is graduated for the purpose) and fixed in its position by two binding screws, shown in the figure on each side of a. Beneath are a second slide and circular plate, counterparts of those above, and the whole is mounted on a plate, P. The manner of using the rest will be easily understood. Hollow andipherical surfaces may be cut with the slide rest with equal accuracy as rectangular figures, either by an adaptation to the common slide-rest, by which the lower slide is made to act upon the other, or by one constructed for the purpose. The slide-rest is of great value in producing any number of pieces of work of exactly the same form, of opposite forms and fitting each other, or in any given proportions ; each elide-screw is fitted with a small circular graduated plate, and sometimes also with a micrometer screw and plate, so that the greatest nicety can be observed.
It ie, howeeer, only in conjunction with the power-lathe, that the full value of the slide-rest Is exhibited. The beat, headstock, and slide-rest of the power-lathe, fig. 10, aro made in the same manner as points, which may be moved out of the way when the cutters approach.
The cutting of toothed wheels is one of the most valuable applica tions of the lathe. [Witert-Currteo.) The circular cutter used In this process may be employed in many other ways, such as cutting grooves and flutes, which, except for sudden curves, it performs better and much more rapidly than the drill. For cutting straight grooves both the drill and cutter are entirely superseded by the planing machine, a modern invention of the greatest importance. It supplies what was one of the greatest wants of the engineer, and might appro priately be called the straight-lathe. For cutting grooves or flutes in cylindrical work, two small puppets carrying centres are screwed to the table to support the work,and the parts where the grooves are required are brought under the tool by means of a divisiomplato fixed to one of the puppets : a revolving cutter may be used instead of a fixed tool for cutting long pinions and terminating flutes.
Eccentric Turning.—In enumerating the different chucka, we pur posely omitted the crcentric and era, as they give their names to the respective kinds of turning for which they are used, and may therefore be considered rather as hurts of the lathe itself than as mere appur tenances. Fig. 13 represents a tingle eccentric chuck. It consists of a in the foot-lathe, but stronger ; the mandril works in bearings to allow the end n to project beyond the back puppet and carry a toothed wheel ; between the beds end along their whole length is a screw, which works in a nut attached to the under part of the rest ; on the end of the screw is placed another toothed-wheel 1), which Is turned by the mandril-wheel a by means of the connecting wheel c. By varying the size of the wheels a and st, the rest can be made to move through any required space along the beds of the lathe at each revolution of the mandril The spindle of the connecting wheel o fits in a curved groove to accommodate it to the different sized wheels used on the mandril and rest-screw; when the rest is required to move in the opposite direction, two connecting wheels aro used. The size of these connecting wheels, having no influence on the relative rates of 13 and n, may be varied according to circumstances. The pulley, instead of being fixed upon the mandril, as in the foot-lathe, is mounted upon a metal tube or cannon which fits and turns smoothly upon the mandril. The lathe, when set in motion, will require no more attention until a fine spiral line is cut, enveloping the cylinder along its whole length ; the rest has then to be shifted to where it started from, or by a simple contrivance be made to work its way back again, the tool being set out a little deeper each time until the surface is completed. In screw cutting with the power-lathe, the point of the tool is made exactly the shape of one of the spaces between the intended threads and having the same rake or inclination; at each revolution of the mandril the rest must move through the distance from one thread to the next. The circumference of the screw has no effect upon any part of the arrangement but the inclination of the tool. When the screw is required to be double or treble-threaded, that is, having two or three intervening spirals upon the Panto stem, the rest must be moved forward a proportionate distance at the commencement of the second and third throttle. In fe. 10, r P P is the drilling frame, for working drills and cutters, fixed In the rest, by aid of the pulleys o, end 1. If it is required to drill any number of holes in a plate, the drill-stock, fig. 11, is placed in the slide-rest and connected with the pulley r. By drawing the drill-frame to or from the centre of the work, holes may be drilled In straight lines across the centre, and. by shifting the dividing-plate, in circles; by the combination of the two movements the holes may le placed in curves and spirals in any direction. By giving Motion to the mandril, and connecting It with the slide-rest screw, spiral grooves cony be drilled upon the surfaces of plates, cylinders, or cones.