I printed two of these up: http://www.thingiverse.com/thing:93652

They work great as long as there isn't any tangles on my spool but any of the "drop-in" spool holders will have this problem. Oddly, the worst spools that I have are the laser cut one's from Printrbot. There are little bumps on the spool plates that cause it to rotate unevenly. This was also a problem using the power tower. I have found that both are useless and now use plastic spools exclusively.

Cheers,

KDog