Timing Belt Y GT2, Printrbot Simple V2

**This will work for both V2 designs (with & w/o string tension). Included is a fan mount to be compatible with aluminum extruder upgrade.**

In response to multiple requests I have developed this GT2 timing belt conversion for the Y axis of the Printrbot Simple. This thing is similar to my original http://www.thingiverse.com/thing:180146

Differences are:
- Use GT2 belt & pulley instead of the MXL
- Use 608 Bearings instead of R2
- Requires some modification of the wood Y axis part