Okay well I actually found that my entire Z axis was loose from the X axis. Strangely though I'd have expected that to make the X axis cut poor but that one was great, lol. Still it couldn't have helped matters. I've also made a modification to improve dust extraction. I haven't tried another cut yet, I'll do that tomorrow.

I'm also considering getting a more suitable tool for cutting plastics. Looking at the Cutwell Tools site.. what do you think is better for acrylic they have 45deg Helix flutes (do these extract the chips better?) plus some YG single flute HSSE and some Karnasch cutters. Are the Karnasch worth the extra money?