by gascarnut » Mon Mar 21, 2016 6:02 pm
Gears are specified in alternate ways:
Diametral pitch (DP): Diametral pitch is an imperial unit of measurement of a gear, and is the number of teeth that would fit on a pitch circle of 1" diameter. So, if you had a 64 DP gear with 64 teeth, it would be 1" diameter at the point where the teeth mesh with their mating gear/pinion. The bigger the number, the smaller the teeth.
The second method is Module: This is a metric measurement system. The Module of a gear is the number of millimeters of pitch circle diameter per tooth. Here the smaller the number, the finer the teeth.
The Slot.it gears will be made in terms of module rather than DP, and they are I think 0.5 module, meaning that a 34 tooth gear would have a pitch circle diameter of 17mm. This equates to roughly 50DP in the Imperial measurement
Remember that the PCD is the diameter at which the gears mesh, not the outer diameter of the gear.
There are exceptions to all of this. For example, Slot.it make their sidewinder gears in both 18 and 19mm outer diameters, and the outer diameter is constant despite different numbers of teeth. They achieve this by mucking with the tooth shape, and that's why some combinations of gears have better mesh than others.
Here ends the engineering lesson for today!