I have cut a fair amount of lexan which is a PITA, to get descent results, I use vacuum hold down, a 1/8" bit and leave a skin on for the first pass. That holds everything together and on the table until allmost all the cutting is done. Then a final pass to cut-through and break the vacuum when the cutting loads are very light because all the high forces happened during the first pass. That "usually" works.
Lexan is bad about sticking to the bit, which tells me my bit is getting too hot, so that calls for less aggressive cutting, same feed rates, but less pass depth.
Hope that helps.
D
"The best thing about building something new is either you succeed or learn something. Its a win-win situation."
--Greg Westbrook