Spur parametric gear rack (experimental)

Warning: not yet printed (and I don't have a printer yet!)

OpenScad script to generate parametric gear racks. Only one important parameter.

There are 4 required parameters:

* module: the most import parameter of any gear. Two gears (or a gear and a rack) of the same module will mesh. Determines the tooth height and this value is the pitch circle diameter in mm. Common gear modules: http://www.beltingonline.com/gears-366/spur-gears-367/metric-0-5-to-8-mod-375/
* number of teeth: this pa