I used to machine a lot of plastics. Delrin, Nylon, etc. Certain times on tight tolerance parts, I would have to check the parts after waiting for the temperature of the parts to return to an ambient temperature before checking dimensions. Some plastics change a lot from just being a little bit warm from just being machined. And too slow of a feed will cause the plastic to melt a bit during the cutting process. I was using a very high FPM/FPT (within reason)with polished cutters and coolant. No burrs, less heat, less temperature deformation. Too high of RPM and a slow feed creates a lot of heat. You just can't get too aggressive, and pull the part of the holding fixture (vice, jaw chuck, etc,,,).
