Hmm, interesting. Balsa should make a superb core, shouldn't it...the attraction of the shopbot NC router is that it gives you the right shape almost directly from CAD drawings. A bunch of the guys here use it to make female molds from high density foam; they cut the molds with the 'bot, then spray on a coating ("duratec" or something), finish sand, add mold release, and get out the vacuum pump. Pretty soon they'll be making blades for small wind turbines that way.

I've heard about tricks with saws and routers and such; yours seems better refined than what I'd heard before and I'll plan to give it a try sometime. Hopefully in a few weeks some "hey look guys" pictures...though maybe not showing the old sweatshirts as bleeder ply. Thanks again for the advice.