Kossel Mini Cross Brace

This is a mount designed to hold cross bracing rod for a Kossel Mini delta printer (https://github.com/jcrocholl/kossel). The default parameters are for a 15mm x 15mm OpenBeam frame which uses M3 hardware and an M5 threaded rod, but could easily be changed to another frame size and mounting hardware.

The Kossel design is triangular and prone to vibration because the upper frame can twist compared to the base. These cross braces provide diagonal support along the upright rectangles, removing the ability for it two twist.

Hardware required to use this design per side of the Kossel:
* Threaded rod of a length determined by the SCAD file (approximately 650mm for Kossel Mini)
* 4x M3 nut (to mount to frame)
* 4x M3 bolt (to mount to frame)
* 2x M5 nut (to tighten the rod on the diagonal)