[mtucker]

I do the plastic bag trick like Metalman when I put a flat spot on the shaft.
Slide your pinion on and see about where the pinion set screw is going to go and then mark that place on the shaft with a felt marker. Cut a small hole in a plastic bag and slide it over the shaft. It only takes a few seconds with the Dremel cutting tool to make a flat spot on the shaft.

You pinion will likely wind up spinning on the shaft if you don't.

Matt