Alright So I uploaded a version with the correct dimensions, Im not sure what happened but my bed dimensions were off. Choose the first file if you are using the original y-axis carriage or choose the second file if you want 40mmx80mm spacing or are using my bed carriage here: http://www.thingiverse.com/thing:2185496.
Be aware that the inherent issue with wobbly y-axis may still be present with the new version, as the spacing on the stock holes is 42mm (as far as I can tell) this seems to be to far apart for the wheels to properly tighten, I was able to easily modify my stock bed to fit this and I recommend doing that as 80x40 spacing is much better. I will print this version as soon as a I have a chance and test it.
I made this wheel tensioner because I was sick of having to, undo the screws, try to fit two tools in there while someone manhandled the printer, plus clamp the wheels so they stayed tensioned, just to tension the y-axis wheels. It works remarkably well(with just one screw driver and no moving the printer). The version Im uploading has a few new features compared to the one that I printed initially, I havent tested this version, but the only main difference is it has a few bridges that might cause some troubles now(but are necessary for the screws to fit recessed without having to use a drill...like I did). The counter bore may need some work, so if anyone prints this and it doesn't work let me now and ill change it. It is 8mm thick so if your someone who counts every mm of your z axis travel(but never even goes near half of it lol), take that into account. If you want to use it for something other than the tronxy X3 the screw spacing is 40mm x 80mm.
It will be fairly tight as is (depending on your printers accuracy) and only needs a very small amount of clamping to make a difference. So put the M4 screws and nuts in and keep them loose then slide it on the extrusion and just snug them up, it wont need a lot...there will be a torque at the base of the standoff that will make the arm want to twist radially outward (probably the major weakpoint I can think of for this system) so it will probably continue to tighten with little more effect, other than to eventually break and twist the wheel until it is improperly seated in the v slot...keep it in mind.
I just reused the M5 screws that came with the printer, although for 2 of the corners it could probably use some shorter screws and it will need m5 nuts.
The holes on the side are for m4 screws and nuts.
I havent used the belt holder yet but it should work.
You'll need two of the clamps and an m4 screw and nut.
I didnt make the clamp(I just split it into a single stl) so credit where it is due to Wisnaeme
If you print this, any comments on how I can improve it would appreciated.