The Gear I created with cliffords Gear Script (http://www.thingiverse.com/thing:829) and the Rack I created using my own quick and dirty experimental Rack Script (https://whatever.metalab.at/user/wizard23/RackGenerator) which takes a closed loop (like a gear or a star, or a heart) and creates the fitting rack for rolling this object.

Cut it out and marvel at the beauty of rolling curves or use it for some playful mechanical contraption you devise.

This rack was calculated with zero slack. After I lasercut it - which makes the cutted thing a tiny fraction smaller because the laser has some width) it rolled very smoothly. If you use this with a CNC you might want to add some slack.