Compound Stage Gear

By Spencer Connor

Technically a compound gear train can be any number of sequential gear sets, although I’m showing the minimum of two and in a straight line. The primary reason to do this is for precise but irrational gear ratio like those often found in astronomical clocks and orreries. For most things a two stage is sufficient and the four gear sizes for a target ratio can be found via Stern-Brocot method or brute force solver. Of course, for greater accuracy it can be expanded to three stage or higher. A secondary advantage of two or more stages is that there is no need for the three or more arbors to be collinear, in fact by ensuring that the input and output arbors are closer than L1+L2 the intermediate arbor(s) can be positioned to tune the depthing of the wheels.