'Printrbot Metal Simple' Back Mounted Dual Spool Holder

In my opinion top mounted Printrbot spools make the machine top heavy and are a *bad* idea due the small base surface area.

This is my version of machine a DUAL back mounted spool holder based on http://www.thingiverse.com/thing:846520 design. I wanted to reduce the width to `60mm` for common `1kg` spools yet still allow for wider spools. To do so I eliminated the end cap and to prevent spools from falling off I slanted the arm `2%` angle - cross your fingers I'm printing right now - DONE,