About this 3D model

Added a probe for an optical endstop, re-enforced the backstop for the captured toothed belt and countersunk the four mounting bolt heads. **WARNING**: See Instructions. See http://www.thingiverse.com/thing:450238 for the matching optical endstop mount for Openbeam 15x15. Timelapse video: https://www.youtube.com/watch?v=VxSCTOD9BZQ