Source code for sp-rocket.com. It generates 3D models of sprockets based on your parameters! If you want to see the code in action, visit sp-rocket.com. It's written in node.js with a very simple server framework I cobbled together myself. It serves static files using the cachemere caching module, but will load modules and invoke methods given a properly-formatted URL.
The ajax URL pattern is:
/~module::function
The framework will attempt to load the module and call the exported function with the following signature:
function(request, response, params)
For the gear-specific code, look at gearlib.js. The meat of the function is in getGearPoints() which uses sin()/cos() to 'walk' a sine wave around the perimiter of a circle, generating the points to use to make the STL mesh.