So, as you can see in the photo, I over-tightened the Z-drive clamps on my Printrbot build. The birch ply is not up to the power of a ham-fisted schlem and eventually cracked through. I looked for an off-the-shelf solution, but I couldn't find two appropriately-sized plates to make the repair. So, first thing I am printing (after minor tweaking prints) is a set of clamps to replace the busted plywood. I am printing it as I type this (without support) and I think it is going to work very well. This is for a Printrbot Plus, but I expect it will work any of the PBs. The groove in the middle that sandwiches the Z drive screw and the shimmed motor shaft is 8mm diam. If you are adapting this for a different 3D printer/application - you may need to modify that.
I printed these with 50% fill, no support, and 2 perimeters and they have worked flawlessly since I made them. I have since looked at the equivalent parts that are part of the Printrbot full tray, and mine are beefier. Even under the strains of my over-torquing fingers, I don't seen any deformation under the bolts. One note, longer bolts might interfere with the carriage on rotation. Make sure your fasteners clear the plywood.
V2 is thinner with nut captives. Based on the strength of the original design, I think some dimensional reduction is in order. This version should easily clear the carriage on your 3D Printer.