This plain description of the device, however, does not convey an adequate idea of its importance. Suppose, for example, that it is required to turn a number of duplicate pieces, each with a certain taper: all that is necessary is to adjust the plates p in their distances from the lathe centres. If the large end of the taper on the work is required to stand nearest the lathe headstock a, the plate p on the headstock must be moved until its shoulder o is farther from the lathe centre. If, however, the work requires to be made parallel, the plates p must be set the same distance for the axial line of the centres. If it be desired to have a parallel and a taper in proximity upon the same piece of work, the tool must have one of its cylindrical ends taper and use it upon the taper part of the work.
Fig. 1317.
In [Fig. 1317] the tool d is shown cutting a square groove. The tool at f serves to turn the parallel part x, and the tool e would cut the V-shaped groove i.
All kinds of irregular work may be turned by varying the parallelism and form of the cylindrical ends b c; but in this event the shoulders o o, [Fig. 1315], should be made V-shaped and hardened to prevent them from rapid wear.
Fig. 1318.