ABSTRACT
When two rotation vectors associated with an input and output shaft are specified, gears of various geometries can be used to transmit and transform a rotation from the driving shaft to the driven shaft. Skew-axes helical gears, worm gearing, and others are used to transmit and transform a rotation from an input shaft to an output shaft, the axes of which cross each other at a crossed-axes angle. This chapter illustrates the possibility of developing a scientific classification of all possible gearings. In spur and helical involute gears, teeth are generated from a basic rack whose pitch plane rolls over the pitch cylinder of the gear; further, the teeth of the basic rack are symmetrical with respect to the pitch plane, or they have, in the case of corrected gears, a plane of symmetry parallel to the pitch plane.
