read post 13 http://www.mycncuk.com/threads/7666-...9535#post59535

these are good starting points for excelent finish. Play with the depth of cut, depending on your machine stiffness and cooling. Blowing air into the cutter from old fridge compressor helps greatly increase the depth of cut. You should have nice chip if you use very sharp polished cutter, which is a must with plastics.