Simple Bearings for Printrbot Metal Plus Filament Spool Holder

For use with http://www.thingiverse.com/thing:675439

These should help reduce the friction load of the spool on the extruder. I found the drag a bit heavy with only the tubes, so I made these to hopefully extend the life of the extruder motor.

Even when snug on the tube, they still seem to loosen the feed tension.

I've added my original blender file (I'm not an artist!) and an untested scad file with comments. I'm finding openscad more to my liking, for functional things such as this.