For Lexan and cast acrylic the optimal settings are very non-intuitive. Has to do with putting the heat into the chip and not the tool, so it won't mark the part.
I had to "fix" a larger more expensive part once. The 3M stuff you get for cleaning up car headlights can do amazing things for fixing and polishing scratches on lexan and cast acrylic.
I don't do much aluminum on CNC at this time.