For finding the distance between the centers of two meshing gears (in inches), you can use the following formula:
(T1 + T2) / (2*Dp) + C
Where:
- T1 is the number of teeth on the first gear
- T2 is the number of teeth on the second gear
- Dp would be the diametrical pitch of the gear (Most of the AndyMark and Vexpro gears have a Dp of 20, which means that the diameter of a gear with 20 teeth is 1". Some have a Dp of 32. You can buy all kinds of neat sizes from other manufacturers)
- C is an additional offset to make up for manufacturing tolerances. If everything could be made perfectly, then C would be 0. In real life, the hole isn't exactly in the center of the gear, the two bearing shafts aren't the exact right distance apart, etc. Most AndyMark products use a value of 0.002" or 0.003" for this offset. You can download some gearbox models and measure the distance from one bearing to the next to see this.