Summary I've updated this a little with the edges radiused which should reduce belt rubbing, and for anyone wanting to modify this themselves I'm including the original 123D Design files. This was my first attempt at anything with CAD, I have one fitted to my printer and it seems to work well, in fact better than the original. The original acrylic part caused the belt to wander from side to side causing belt wear. You can see in the picture the side of part of the belt is showing wear where it was rubbing on the sharp acrylic edge. I hope others may find it useful. If you have any feedback please leave a comment. I believe this is the same for the aluminium and acrylic models. Mine is the aluminium model with some acrylic parts, I made this just in case.... http://www.thingiverse.com/thing:953556 has all of the other parts except the Z axis top mount.