I just made my first two 3" minicell bulkheads and here are a couple of tips for those who have not tried it before. I am sure that there are other ways to do it...maybe better ways but this worked for me. These were for my Great Auk.

1. If the bulkhead falls on or very close to one of your forms then trace that form on the minicell. I used my lofted half sheets and not the plywood forms.
2. If it falls between two forms then trace both the larger and smaller form on the minicell.
3. Take a look a the average difference in the two tracings. I am sure that there is a mathmatical formula you could figure out....but I figured it looked like less than a 5 degree angle. I set my bandsaw table top to 3 degrees and cut the bulkhead using a narrow scroll blade.
4. I picked a point just over (1/8" or so) larger than mid-way between the two traced lines and cut it out. It fit the first time with no sanding.

Second tip...do the larger of the two first, that way if you mess up the first one you can probably salvave it for the smaller bulkhead.

The minicell is pretty pricey so I did not want to mess it up.

Jay