Printrbot spool holder with bearings

Emmett's Printrbot spool holder (http://www.thingiverse.com/thing:355889) was one of my first prints, because, of course, the Printrbot Simple Metal ships without any spool holder.

The spool holder worked great, and made long prints feasible. But every once in a while, with a very full spool, the filament would fall off the spool and wrap around the spindle underneath, and then get stuck, stopping filament movement and ruining the print. Also, as a trivial nuisance, the rubbing action of spoo