Wow! I made a post and it looks like it never happened. My suggestion was to download OpenScad and then go to http://www.thingiverse.com/thing:3575 and get the parametric_involute_gear_v5.0.scad file. It can even make Herringbone gears. This is the module that most of the RepRap's use to make their gears. You get to specify everything.