Back gear

(in a lathe) one of several gears for driving the headstock at various speeds.
Historical Examples

Referring again to Fig. 494, g′ is the pinion to drive the back gear while g receives motion from the back-gear pinion.
Modern Machine-Shop Practice, Volumes I and II Joshua Rose

Various methods of moving the back gear into and out of gear with the cone spindle gears are employed.
Modern Machine-Shop Practice, Volumes I and II Joshua Rose

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.
Modern Machine-Shop Practice, Volumes I and II Joshua Rose

The cone pulley and back gear is of the full proportion and power of an eighteen-inch lathe.
Modern Machine-Shop Practice, Volumes I and II Joshua Rose

Another plan is to let the back gear move endwise and bush its bearing holes with hardened steel bushes.
Modern Machine-Shop Practice, Volumes I and II Joshua Rose

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.
Scientific American Supplement, No. 643, April 28, 1888 Various

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