I'm working on some blast gates for 6" PVC duct work. Based on the link on Bill Pentz's site I've been trying to cut a 6" hole in 3/4" MDF, Mellamine, or Plywood. I have a circle cutter and I'm using my new Delta floor drill press on the lowest speed (215 RPM). This works, but it is very slow and the cutter is nice and blue after just one hole. I used very little pressure on the cutter.
So, what is recommended? I could use a jig saw, router with a circle jig, buy premade gates from LV or ClearVue. What else is out there I haven't thought of? Oh, I have coupler ends on the PVC now so I was going to make the gates with short pieces of standard pipe.