Fig. 1148.
To increase the steadiness of the sliding head it may with advantage, be made long, as in [Fig. 1148], in which s is a long sleeve fitting to the bar b at the head end h, and recessed as denoted by the dotted lines. The short cutting tool c may be fastened to h by a set-screw in the end of h, or by a wedge, as may be most desirable. The bar may obviously set over to bore tapers as in the cut, and the sliding head may be prevented from turning by a driver resting on the top of the tool rest, and pushed by a tool secured to the tool post, the self-acting carriage feed being put in operation.
Fig. 1149.
It is obvious that when a boring bar is set over to bore a taper, the lathe centres do not bed fair in the work centres, hence the latter are subject to excessive wear and liable to wear to one side more than to another, thus throwing the bar out of true and altering the taper it will bore. This, however, may be prevented by fitting to the bar at each end a ball-and-socket centre, such as shown in section in [Fig. 1149]. A spherical recess is cut in the bar, a spherical piece is fitted to this recess and secured therein by a cap as shown, the device having been designed by Mr. George B. Foote.
Fig. 1150.