3rd Rail CoreXY

*UPDATE* I have retired this version and moved on to the V2. You can find it here: https://www.thingiverse.com/thing:5319298. (TL;DR This is a coreXY conversion for the FlSun Cube, but it works for scratch build printers that use 2020 extrusion and MGN12 rails. It assumes that you have a Z axis setup that you already like.) After a year of trying, I was never able to get my FlSun Cube to print as good as I wanted. Despite costing more, it was consistently giving me worse prints than my abused Wanhao Duplicator i3--mostly due to having very not-straight 8mm rods. Also, lets face it, the stock gantry configuration is really inefficient and weighs in at a whopping THREE POUNDS. There had to be a better way. 3rd Rail is my attempt to find that better way. I dropped the 8mm rods in favor of MGN12 rails and changed the complicated kinematic arrangement out for a more elegant CoreXY arrangement. The nice thing about the rails is that they are pretty resistant to racking, so you can get by with similar quality choices as the stock printer. This is based upon the 5rails build, but has been customized to work with the frame and Z axis arrangement from the FlSun Cube. I added extra ease space for the belts (my Chineseum belts were thicker than expected) and modified the X to Y brackets to give full access to the stock Cube build plate. Compact 8mm rod holders are used at the top, to give full range of motion (they are friction fit and meant to hold the rods in place. Use the stock holders at the bottom to make it secure.) The Unimount replaces the idler mounts from 5rails with a taller and ambidextrous version. For whatever reason, my belt path was substantially taller than the stock 5rails mounts allowed for. I also added a bit more belt ease space. In the end, I have a full 310*310mm build plate with a 430mm maximum Z height. This arrangement weighs about 1lb less than the stock gantry arrangement. That XY range may be reduced, depending on what hotend and