Simple^2 Anti-Tension Customizable Spool Holder for Printrbot Simple Metal 1403

Using other z-rod-mounted filament spool holders, I found that they caused undue tension on the filament when using fast retraction. The ones that tried to resolve this relied either on metal bearings, or overly complex (and large) solutions.

Not finding a suitable one that I liked, I designed my own in OpenSCAD.

The design allows the filament guide arm to flex on resume from fast retract, instead of having the full tension of the retract have to spin the mass of the entire spool. In