This completes the lathe itself, but many adaptations are necessary before it is in order for work. Of these the principal are the chucks used to connect the work with the lathe. The screw-chuck is a circular plate of metal with a boss at the back, tapped to screw upon the nose of the mandril : the face is turned perfectly true, and in the centre is a coarse conical screw to hold any large piece of wood to be turned. The hollow-chuck is a strong circular cup of metal with perpendicular sides : the work is either driven into it with a mallet, or, if smaller than the inside of the cup, held by the ends of four screws in its rim. The drill-chuck is a strong iron chuck about an inch in diameter, with a square hole in the centre to receive drills and other tools. In drilling, a mark being made with a punch where the hole is to be, the work is held against the point of the drill, and the front-bead being brought up to the back of the work, the cylinder is pressed forward, as the drill proceeds, by turning the screw J. The 'universal chuck is a circular disc of metal, with three narrow elite cast in it, extending nearly from the centre to the circumference. The face is turned perfectly true when on the mandril, and the work being laid upon the face of the chuck, is fixed to it by screws which pass through the slits into nuts at the back of the plate. The concentric chuck is of the same form as the last described, snd the face in like manner must be turned per fectly true to the mandril. Instead of three slits, it has but two, in a straight line with each other, and extending nearly the whole diameter; the opening of these slits is wider at the back than front. Within these slits lies a spindle, having a bearing in the centre and one at each extremity, with a right-hand screw upon one and a corresponding left hand screw upon the other ; these screws move two steel studs which fit accurately within the slits, and have projecting heads about an inch square, that move steadily and smoothly along the face of the chuck. Upon the heads are fitted two other square pieces, having their sides hollowed out in curves of different diameters varying from two to eight or ten inches, and which can be placed with either of their sides towards the centre, to fit the circumference of the work to be held between them.
All the chucks that we have described are adapted principally for work which does not require supporting at both ends. When a long piece of wood is to be turned, a chuck is used having a piece of steel with three points standing out upon its face ; the centre of one end of the work is pressed against the middle point, and the other end is supported by the cylinder of the front-head.
The carrier is used in metal-work for the same purpose as the three point chuck for wood. If the ends of the work are pointed, it is supported between the hollow end of the cylinder in the front puppet El, fig. 4) and the nose of the mandril, which is similarly shaped for the purpose : if, on the contrary, the ends are hollow, the cylinder is reversed and the point-chuck. (fill. 5) screwed upon the mandril. The carrier (c, fig. 4) is fixed upon the end of the work by its screw, as shown on a larger scale in the side view ,fig. 6; and motion is given to
the turner holds between the upper part of his arm and his side. For hard wood, ivory, and bone, similar gouges and chisels are used ; but they are smaller, and sharpened at a less acute angle. Some of the work, as in gold, silver, and light brass-work, is performed by gravers with straight, oblique, and curved faces, to suit different sorts or parts of the work. These are sharpened by an angle on the under side only, and the cutting-edge is applied nearly opposite to the. centre of the work. For inside work, drills placed in angles are used to make the first opening, which is afterwards enlarged by other tools with this general characteristic, that the stalk is made narrower than the cutting part of the tool, to allow of undercutting or making the hollow within larger than the opening through which the point of the tool is intro duced. The principal tools used for turning iron are the hook-tool, fig. 8 E is the cutting-edge; the heel, H, is placed firmly upon the top of the rest and the tool held with both hands, the end of the handle resting against the turner's shoulder. For finishing the work, gravers of difibrent sizes and shapes are used, similar to those for hard wood, gold, silver, brass, and ivory, but stronger, and sharpened at a more obtuse angle. Screw-tools are very important appendages to a lathe, and, with the engineer, in constant use : they are filed up with several teeth exactly the shape of the spaces between the intended threads. For inside screws the teeth are cut on the side, instead of the front of the tool : taps however are much more generally used. A circular saw is often fitted to a lathe, particularly for ivory-turning : the saw is placed upon a spindle against a projecting collar, and held in its place by a washer and nut. A parallel rule is fitted upon the table by the side of the saw to regulate the width of the pieces cut off.
In the lathe, as previously described, the tool is held in the hand, and is consequently subject to any unsteadiness in the workman. To get rid of this imperfection in certain cases, and so arrange that the tool could be withdrawn at pleasure and replaced in the same position, and always be steady, was a great desideratum. This was effected by the invention of the slidc-rest, which is now attached to all but the most ordinary kind of lathes. The principle of the slide-rest is that the tool is fastened to a plate, moved in the required direction by means of screws, instead of being held in the hand. Fig. 9 shows a the work by the driver n, jljs. 4 and 5, either screwed upon the nose of the mandril or attached to the point-chuck.
Wood and ivory turners make use principally of box and other wood chucks altered at the instant to suit their purpose. One chuck, how ever, requires notice, called the split or ring-chuck, fig. 7 : a piece of wood is tapped and screwed on to the mandril and then turned conical; it is afterwards drilled down the centre to the bottom, and two slits cut with a saw at right angles to each other, from the point of the chuck to the nose of the mandril; the work, when in the chuck, is held in its place by the ring on the outside.