Fig. 823.
[Figs. 822] and [823] represent a chuck employed by the Hancock Inspirator Co., of Boston, for very true work. This chuck will not get out of true by wear, and holds brass work against a good lathe-cut without indenting it.
Fig. 824.
[Fig. 822] shows the chuck complete. [Fig. 823] is a mid-section of chuck complete. [Fig. 824] is a side and an end of the work-gripping piece. The chuck is composed of three pieces, a, b and c. Piece a screws upon the lathe spindle and is bored to receive c; piece b screws upon a and receives the outer end of c, which is provided with a double cone d e, and is split nearly its full length at three places, one of which is shown at f, so that when b is screwed upon a the two cones upon a, b compress c, and cause the diameter of its bore to decrease and grip the work. The splits f are made long, so that c shall not close at its outer end only, but on both sides of the cones, and thus grip the work parallel.
There are several advantages in this form of construction; thus the parallel bore of a, in which c fits, is not subject to strain or wear, and therefore remains true and holds c true. Furthermore, b has no tendency to wear out of true, because it fits upon a at the part g, as well as at its threaded end, while the cone e of c also acts to keep it true. As b is screwed up with a wrench fitting its hexagon exterior, the work can be held against any amount of cut that the lathe will drive.
It is obvious that the capacity of the chuck, so far as taking in range of different diameters, is quite limited, but the excellence of its execution far more than compensates for this when work is to be turned out true and correct to standard gauge.
To increase the range of capacity of the chuck, the split piece only needs to be changed. Before hardening the split piece the jaws should be sprung well apart, so that they will spring open when released by unscrewing the outside shell to release the work and insert another piece.