Hi Brian
Basically it is like this......whatever shape you want, in every detail including a lip or flange at the base of the cowl if it is going have that........you make it to that shape....just like it will look when it is a part. There are many ways to go about this. What works good for me is balsa blocks. I carve the plug from balsa and then check it with templates when I have it down to the shape that I want. I like to use balsa for several reasons. It is easy to sand and shape yet is tougher than a foam block. All it takes is resin coating to make it smooth with a tough skin whereas other materials take more filling and fairing and sanding to get the suface perfect. Once it is resin coated and sanded smooth I shoot it with about 50 mils of Dura Tek, which is a catalyzed primer. The pimer gets wet sanded and polished up to a good gloss (Dura Tek will polish up to a mirror finish) then it is ready to wax and lay up the mold. It is really up to your imagination. All you need is the shape with no negative draft angles. Severe negative drafts will make it impossible to separate the plug from the mold. Hope this helps.
Mark
