Here is a solidworks file used to design a 3 CIM gearbox:
https://drive.google.com/file/d/0ByD...ew?usp=sharing
It has a 50 tooth gear in the center, with three cims with pinions driving it. On each cim we have included 3 different sized pitch diameters (12, 14, 17) so that the pinions can be swapped to get different ratios. Each pitch diameter circle is driven by an equation: pitch diameter = number of teeth/ 20 +0.002 because these are 20 dp gears. I have also added 0.002" to all pitch diameters to get the 0.002" extra on all center to center distances. Also included in the first sketch are mounting hole locations for the cims with each of the different pinions. Around each pitch diameter I have a circle 0.1" larger in diameter to show where the tips of the gear teeth are to make sure nothing will collide with them. Also shown are the bolt heads of cim mounting screws to make sure everything will clear.
The 0.002" extra value is not a strict rule. We have found that it works well for enclosed gearboxes that are waterjet.
I wish solidworks had sketch annotations so I could label every circle. It can get ridiculous trying to remember what each of the dozens and dozens of circles represent when doing a more complex gearbox.
Here is a screenshot of the assembled gearbox:
https://drive.google.com/file/d/0ByD...ew?usp=sharing
The cim mounting hole locations in the plate that the cims mount to is driven by the sketch in the front plate, so that any change made to the front plate will propagate through the whole assembly.
These gearboxes are a good example of how you can use solidworks bottom-up (start with sketches) or top-down (start with assemblies and use the parts to drive sketches for other parts). For example the gearboxes start with sketches, but the robot bellypan uses components placed in the assembly to drive the position of mounting holes.