Update 11/8/2016
After printing this again for the left side with the cable, this side was 2mm longer opening, so I made a Long & a Short version. I also realized their are 2 nice holes on the aluminum vertex to wire tie these in place instead of using a T-Nut. You can see a 8" black wire tie on the left cover of the 1st photo. There are still a number of options in the openscad file if you prefer to print it a little differently. I also allowed 2mm more clearance in front of the belts.

I would suggest printing VerticalBelt_GuardShortTest_Rev12.stl file 1st to see how well it fits on each of 3 vertices.

I occasionally have something fall thru these openings and sometimes plastic debris gets caught in the belts, so I came up with this idea. I have included an openscad file & 4 stl files. There are 2 T-Nut screw holes on each side, but it was a tight enough fit on my machine that I do not need them. In the openscad file you can set a few variables, like the base height, Belt Guard height & opening for Effector cables. I set the base height at 2mm & height for the belt guard at 30mm, but you can go to what ever height you want.

I have only tested this on an hour print & not sure if there needs to be some ventilation holes for heat from the motors so I added an option for putting in heat vents above the motors if anyone has problems with heat not venting.