This is a great way to keep stepper motors cool.
This thing is a remake of http://www.thingiverse.com/thing:22449, with freecad python sources provided.
I had issues getting ChrisMagno's part to slice with slic3r, so I rebuilt from scratch.
Printing an assembly are straightforward.
The freecad python source should work by copy-paste into the freecad python shell. Freecad version 0.10 has some issues with the script and will not produce reliable results, but it works fine with freecad 0.13