be found to answer every purpose. This is the best form of stay I know of, but some workmen, instead of the die and holder, use a piece of plain iron shaped like an inverted L, and attached to the standard on the slide-rest, in the same manner as the die-holder is in this arrangement.

A socket bearing is merely a hollow cylinder of iron, fitted with six or eight screws, and sometimes used when turning portions of long shafts. It is slipped on to an unturned or rough shaft, and by moving the set screws is adjusted so that its surface runs true. The socket is then used as a bearing for the shaft, by being caused to run in the dies of the die-stay shown at Fig. 128.

Another modification of this bearing is sometimes necessary, as, when the shaft to be turned has large collars on it, the socket cannot be slipped on to the shaft. In these cases, a bearing such as the last is used, but made in halves, which are put together, when on in place.

The four-jawed chuck, Fig. 144, is a very useful contrivance for chucking and holding work whilst being turned or bored; it is very like an ordinary face-plate, but has four jaws on its face, which are moved in or out, towards or from the centre, according to the size of the work, by turning the screws at the edge of the plate. These jaws being turned out in steps, articles varying greatly in diameter can be chucked without much movement of the jaws. Articles such as rings may be chucked or held by their inside surface by putting them on the outside of the jaws and screwing from the centre.

There are various modifications of this chuck in use, in which the jaws are simultaneously moved towards or from the centre, without having to move each by a separate screw. But these self-centering jaw-chucks, as they are termed, are useful only for circular work, whereas the one described will chuck

work of almost any shape. The self-centering chucks are, however, much liked by amateur mechanics, but are not used to any great extent by practical men, as, although occasionally convenient, most varieties are too clumsy and complicated to give continued satisfaction. A self-centering chuck is shown at Fig. 145, by moving any one screw the three jaws move together.

The tools used in the slide-rest for self-acting turn

ing are various. The ones described have been found effective, and they are as simple as any. Most work

Amateurs are fond of universal tools: mechanics seldom or never use such, and although they are very pretty to look at, their use cannot be recommended.

Fig. 146 is the ordinary hook tool. Fig. 147 is the

FIG. 146. FIG. 147.

side-hook tool; these are made for cutting both to the right and left hand. Fig. 148 is the square-nose, Fig. 149 is the round-nose tool. Fig. 150 is the knife tool, made both right and left hand. Fig. 151 is a simple

roughing tool. Figs. 148, 152, 153, are spring tools. Fig. 154 is a simple tool and holder, sometimes made with a triangular instead of a round tool. This tool is merely a piece of round steel, ground off as shown. Fig. 155 is something like the last, but adapted to light work: the tool is made of a flat piece of steel, ground and held in a holder as shown. The cutting part of this may also be made with a round edge, with a square edge, or with an angular edge. Such tools all work very well, and are both easily made and readily ground when dull. Upon the whole, the

FIG. 152. FIG. 153. FIG. 154.

FIG. 155. FIG. 156. FIG. 157.

amateur will find these tools and holder to be as useful as any he can get. Fig. 156 is the ordinary holeing tool. Fig. 157 is the compound holeing or internal turning tool.

The metals turned by these operations being those already mentioned, no further remarks on them will be necessary; but work to be turned by self-acting tools requires different treatment, in some respects, from that of the same material turned by hand-tools.

The tools described are all held in the tool-holder of the slide-rest, and the screw or screws holding them should be screwed down reasonably tight, but care should be taken not to strain the screws or damage the screw-thread. Many workmen fancy they cannot use too much force in screwing down their tools. They pull with all their power at the end of a long lever in the shape of a wrench, and the result is that their screws are frequently either breaking or having their threads sheared off. The tool should not project too far outside the rest or support, as the nearer the cutting edge of the tool is to the support, the better the tool will work; but it is not necessary, if the tool be of the proper size, to work it close to the rest, nor is it convenient to do so.

Slide-rest tools should not be double ended, or made with a cutting edge at each end, as, when this is done, the end not in use seems to be always in the operator's way, and inflicting serious cuts on his unfortunate fingers. The steel for all the tools should be of the best quality. It seems bad policy to use soft or cheap steel for these purposes. Some use Bessemer steel; but, admirable as that metal is for constructive use, it can scarcely be recommended for tools, and, however costly the best steel may be, it is the cheapest in use.

The cutting edge of the tools should be just level with the centres, but the slide-rest tools, for internal turning or boring, may be placed above the centres with advantage. The practice in the matter of speeds varies somewhat in different workshops, and with different workmen; but no exact rule can ever be given,