hold down plastic

Hello everybody
This is first time I have to doing machining on derlin/plastic I have to do machining outside profile & on center hole(9”) from 24”x24”x0.750” derlin /plastic what is the best way to hold down plastic. I don’t have any vacuum devices’. Please help me for which end mill I can use with recommended speed, feed, and depth of cut. Any suggestion helpful

Here's one way;

Doublesided tape, and a few clamps around the outside. Cut the center hole, and move the clamps. The tape will keep your Delrin from moving while you shuffle clamps, then profile the outside.