Parametric marble roller bearing for cheap filament spindle

This is a derivative work of http://www.thingiverse.com/thing:4641 and http://www.thingiverse.com/thing:4885 .

It is designed to be Makerbot printable.
The idea is to have the roller bearing filled with marbles and have some board with the filament on top of it freely spinning.
For the board you can use cardboard, press board or whatever is lying around. I used some of the wood left from the makerbot assembly.

To increase resistance against tilts and asymmetries in the filement spindle i