Here is something I have stumbled on to that gives professional results.
My latest project is to change out my woofers from a pair of Altec 414Z woofers per channel, for some 2231 with 2235 cones, two each a side as well. Aha! I thought I finally had a use for the new spin saw....no such luck, the circle cutting jig only allows up to 12" diameter holes.
The prospect of using a jigsaw guided by hand was not too inviting, my experience at getting a hole with a decent shape has not been great.
I looked around and found that Lee Valley Tools had the perfect solution for C$31.50. It can make holes from 6 to 40" in diameter. It's a plastic universal cutting router jig that allows you to exactly drill a pivot point for a 13-31/32" diameter hole. You simply remove the base of your router, (oh yeah - Sears had plunging routers on sale for C$99.00), and screw the jig to the router.
The jig comes with a 1/8" post that goes through the pivot hole you make in the jig and into a 1/8" hole in the center of your cut-out.
Presto, perfect holes in about a minute through 3/4" MDF. I can't believe just how easy it was to cut four woofer holes.
www.leevalley.com
P/N 46J91.01