Re: HDPE question
UHMW and HDPE are both polyethylene. The UHMW has a higher density, but other than that no substantial difference for most applications. If I wanted a ''see through'' something for an application requiring strength and resilience, polycarbonate (Lexan, Tuffak) would be my choice.
Warping is common when machining some plastics (and some metals), but if you take off about the same amount of material from each side you can minimize this. In your case, heating the material and trying to straighten it might work, or it may get worse. Just depends on the stresses in the material.
Jim Dawson
Sandy, Oregon, USA