X Axis motor mount for Anet A8 or Prusa i3

This is a ground-up redesign of "thing" 1428253 using Fusion 360. I used a slight teardrop shape at the top (when printing) of the horizontal holes to avoid sagging on the bridging at the top of the holes. I also used 1mm fillets at all of the corners, so the printer would not have to slowdown or overrun tight corners. These changes allowed the tolerance to be a lot tighter than the original design. The holes are 8.18mm (originally 8.6), although I did have to use some light bearing oil to slide the rods in. Linear bearing holes are slightly tighter too (15.08 vs. 15.2). There are other cosmetic and functional changes.

After you print, you probably want to sand the bottom (that will be the top when flipped). I used 600 sandpaper. This is in case there was any curling/warping off the bed during printing. You want those huge nuts for the z-axis screws to be as level as possible.

All of the screws and nuts are 3mm in my design. I used a left over 45mm screw from my printer for the pulley/thumbscrew. I also used 3mm locknuts, although plain nuts should work too.

###Printing
* Depending on your printer, use either the standard Left/Right files which have 45mm spacing between rod axes, or the 44mm/46mm variants of those files.
* Do not use supports
* Enable Avoid crossing perimeters or equivalent so you don't have any garbage to clean up where the rods or linear bearing go.
* The test_fit.stl file can be used to check how tight the fit is with your printer and slicer settings. The hole in this file is the normal (8.18mm) size.

###Assembly
After inserting the horizontal rods, rotate both of them in place (simultaneously) to relieve any stress on your Z-axis rods. Then tighten the two outer screws on the "tensioner" just enough that it begins to separate. This ensures that the horizontal rods are providing the belt tension (and not your Z-axis).

###Updates:
* I added a second version of the right side that is slightly looser than the left side, in case you don't want to struggle to slide the rods across. It is 8.32mm instead of 8.18mm.
* Made the screw holes for the endstop switch a little bigger
* Added a small shape for test-fitting just the hole
* Added variations with 44mm and 46mm rod spacing (vs. standard 45mm)

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