I've created a lot of 3D printed gears over the last few years and one of the best tools I've found is from Rainer Hessmer.<p><a href="http://hessmer.org/gears/InvoluteSpurGearBuilder.html" rel="nofollow">http://hessmer.org/gears/InvoluteSpurGearBuilder.html</a><p>It allows you to specify additional parameters like backlash, clearance, and profile shift. It also allows you to output in DXF which tends to be more of a standard in the engineering world.