Back-Gear

In an engine-lathe for metal turning or in a drill or milling machine, a short shaft parallel to the spindle which carries the nest of cone-pulleys. On this short shaft are two or three toothed wheels. The cone-pulley casting which carries the belt has cast or fastened to it a small gear which engages with a large gear on the back-gear shaft. The cone pulley casting turns freely on the spindle. At the other end of the back-gear shaft is a small gear which engages with a large gear keyed on the spindle of the tool, so that the driving speed and power of the belt is carried round the nest of cone pulleys back to its axis again with great reduction in speed and increase of power. The usual ratio of gain is as 1:10 or as 1:16. In lathes which are triple-geared there is a third wheel on the back-gear shaft, so that at will the spindle may be driven by the former gear, or the face-plate or chuck-plate may be driven from teeth on its periphery, by this third wheel. See LATHE.