Two classes of cutter-bars are represented by Figs. 456 and 457, one class being cylindrical boring-bars or rods; these are used in lathes by being rotated while on the conical pivots termed lathe centres. The other class of cutter-bars consists of square bars that are similar to other slide-rest tools, and are bolted to slide-rests in a similar manner. A cjdin-drical boring-rod has two or three slots, termed cutter-holes, for tightly holding the cutters while in use. In the Figure a cutter is shown to be keyed in its place ready for use, the cutter being denoted by C. A boring-tool of this class is used to bore wheel-bosses, lever-bosses, tubes, garnishers, and many other pieces of work that are too long to be bored on a chuck.

The slide-rest tool shown by Fig. 457 also has a cutter, denoted by C, but this tool is employed for making grooves, key-ways, and similar openings into wheel-bosses and lever-bosses after they are bored to their finished diameters, the key-ways being made with the cutter-bar while the piece of work is still bolted to the lathe chuck. The method of using this bar consists in tightly bolting it to the slide-rest and moving the rest to and fro ; by such means the cutter is made to traverse the entire length of the hole in the wheel or lever that requires the key-way, and cuts out a portion of the metal every time the cutter enters the boss. In small lathes, the rest to which the cutter bar is fastened is moved to and fro with the ordinary handle ; but rests and carriages that are too heavy to be thus handled are moved with the aid of the lathe-screw and a few wheels.