Today’s project was a clear pick-guard to replace the standard black one you’ll find on an Eastman AR371-CE guitar. The fellow specified 5mm Lexan polycarbonate as his preferred material - a super hard plastic that’s very difficult to break - it’s basically what they use on greenhouses in lieu of glass.
It cuts pretty well but needed a pretty slow spindle speed to prevent it from melting to the cutter. And air - as much air as you can blow at it..! I used a 3mm 2 flute carbide end-mill - this is perhaps why the spindle was set to a slow 9500rpm, plastics are usually cut with single flute cutters, which would allow a higher spindle speed. Full width depth of cut (roughing pass) was twice around at a depth of 2.5mm with a 10mm/sec feed. The finishing pass to take off the 1mm left by the roughing pass was the same but just once around at full depth. After that the edges needed smoothing back with 400 then 1500 wet’n’dry before polishing them up with Autosol.