While the paint dries on some other parts, I decided to begin fabricating an avionics access door that will go in the bulkhead between the instrument panel and the firewall. I began by taking a bunch of careful measurements of the bulkhead, then I spent some time planning the operation of the door and the details of its construction. (It will hinge at the bottom, and the door will open forward, into the baggage compartment. I think I'll fasten it with #8 screws and nutplates, but I'll look at quarter-turn fasteners, too.)
I measured and drew the design onto the bulkhead so I can cut out the opening, and also copied the door dimensions onto a sheet of white posterboard. After checking the clearances and verifying that my concept will work, I then used this "posterboard door" as a template to cut out the actual door from a sheet of 0.040 aluminum.
I also cut the -P3 hinge that will mount the door. By the way, for reference, my door will be 23.5" across, 6.5" high in the middle, and 4" high at the outside edges. The actual opening in the bulkhead is 3/4" less than this on the top and sides. That's where the nutplates and reinforcing ring will go.
You might notice that the opening will not quite reach the tops of the indentations in the bulkhead. That's OK, because the door will cover this area, and the nutplates will be located between the indentations.