We mill plexi and acrylic faces with a 1/4 shank 3/16 cutter. Onsrud makes them. They are single flute upspiral 65-018. As far as feed rates - you can tell by cutting your material. If you are going too slow - you'll get extremely fine chips - too fast - fills the cut gap and the chips re-adhere themselves gluing your channel shut. We'll take 1/2" passes with this bit.