I don't need a physically accurate function, but something that hints at the involute curves, etc. I was just using `r = 2 + sin^2`, which gets the idea across, but it looks like - ahem. Googling around, you can find plenty of information on how to draft a 'correct' gear, but nothing in the way of a bare-bones approximation.

EDIT: The 'look' that I'm after: <http://www.cartertools.com/involute.html>