Referring again to Fig. 494, g′ is the pinion to drive the back gear while g receives motion from the back-gear pinion.
Various methods of moving the back gear into and out of gear with the cone spindle gears are employed.
As shown in the sketch, g is in one of these grooves while h is the other, but when the back gear is in, g would be in h.
The cone pulley and back gear is of the full proportion and power of an eighteen-inch lathe.
Another plan is to let the back gear move endwise and bush its bearing holes with hardened steel bushes.
The head stock of a lathe—the back gear in particular—is about as hard a thing to improve as the link motion of a locomotive.