3D Printed Wheel + Axle, Parametric

Here' a basic, parametric definition for toy wheels, created in Rhino + Grasshopper.

The "axle" has a square shaft for assembly into whatever vehicle you dream up. The part is generated with a user-defined gap between the hub and wheel (0.4mm worked well for me). You can also include a through-hole to use a nail or screw for a more durable toy. In the included photo, I've used a small nail to lock in the 3D printed wheels. The nail does two things: (1) reinforces the plastic where the hub narrows to the plastic axle and (2) expands the axle section for a tighter fit into the hole. You could use glue, but I found that the nail does a great job of locking the wheels on. The reinforcing hardware allows you to use a much smaller axle size (that can stand up to enthusiastic toddlers).

I used these wheels on my [Modern Diesel Train](http://www.thingiverse.com/thing:1994173). After assembling onto the train and hammering in the nails, I had to work the wheels back and forth to snap the