Fig. 1529.
Fig. 1530.
The mechanism for swivelling the upper part or body upon the base and for locking it in its adjusted position is shown in [Figs. 1529] and [1530]. The body d is provided with an annular ring fitting into the bore of the base, which is coned at q. The half-circular disks r fit this cone and are held to the body of the chuck by four bolts n, which are adjusted to admit disks r to move without undue friction. k is a key having on it the nut v, which receives a screw whose squared end is shown at s. By operating s in one direction key k expands disks r, causing them to firmly grip the base at the bevel q, hence the base and the body are locked together. By operating s to unscrew in the nut v, k is moved in the opposite direction and r, r release their grip at q and the body d may be swung round in any position, carrying with it all the mechanism except base p.
To enable the body to be readily moved a quarter revolution, or in other words, moved to a right angle, there is provided a taper pin, the base having holes so situated that the body will have been moved a quarter revolution when the pin having been removed from one hole in the base is seated firmly home in the other.
Referring again to [Fig. 1526], there are shown one pair of parallel pieces marked respectively a, having bevelled edges, and another pair marked respectively b. Both pairs are provided with a small rib fitting into a groove in the jaws of the chuck, as shown in the figure.
These ribs and grooves are so arranged that the upper pair (a, a) may be used in the place of the lower ones, and the uses of these pieces are as follows:—