What plastic for Printer Parts

[printbus]

... For example, the v slot wheels on my z don't all spin when the z is moving up and down. I can freely spin the inside wheels.

This indicates to me that you did not have the left x-motor and right hand x-idler brackets properly adjusted to the vertical rails and the two brackets level with each other BEFORE you tightened up the horizontal rails to the end brackets.

EDIT: ...regardless of whether or not the build guide was clear on doing this. It certainly wasn't mentioned in the April 2014 build guide that I used.

EDIT #2: With the horizontal rails loose on the x-motor and x-idler brackets, adjust each of the x-axis brackets to their respective vertical rails. Then level the two x-brackets using the method of your choice. I used a long metal ruler as a straightedge across the top of the two brackets. Others have adjusted for something like equal distance between the bottom of the brackets and the tops of the z-motor mounts. Then, and only then, tighten the horizontal rails to the x-motor and x-idler brackets. Tightening the eight M5 bolts on the horizontal rails will likely torque the x-axis assembly out of alignment, so some readjustment or pre-tensioning in the opposite direction may be necessary.