Parallel gears - Geometric study

A gear is a device that connects two shafts, transmitting rotational motion from one of the shafts (the driving or motor shaft) to the other (the driven shaft), with a constant ratio of angular speeds.

Depending on the relative position of the two shafts to each other, we have three main gear classes:

Parallel gears: the two axes are parallel (figure 1 a).

Concurrent gearing: the two axes intersect along their extensions (figure 1 b).

Left-hand gear: the two axes occupy any relative position; they are neither parallel nor intersecting (figure 1 c).