That's a hell of a site you have there Cafeman. I've seen several of your posts but never knew of the link. I'll be sure to read through the other things as well. The thing is I need to cut a hatch through the bottom of an ultra stick 40. I could go through the top which is balsa but I figured it would be less noticeable from the bottom. It is ply and pretty thick. What I want to do is put a lighter engine mount on it. I've knocked the blind nuts out and need access to the firewall from behind to fill in the old holes with epoxy and to reinstall them. I will also be tail mounting rudder and elevator servos. Your information you provided will be a big help there. Thanks.