My nephew (in Atlanta) asked me how to cut a 10" diameter hole in 3/4" hardboard. (I didn't even know they made 3/4" hardboard! Anyway, I didn't know, so I'm going to the experts. He has a jigsaw and a router available. I wasn't sure what kind (TPI) blade to use in the jigsaw. I thought several light passes with a router on a trammel would work. Any ideas?