I've been doing tiny chunks of work the last few days and need to get caught up with pictures. I finished the hinge halves that will get riveted to the seat pan and match drilled them. These mate up to the other hinge half on the bottom of the seat back and provide a few inches of adjustment fore/aft.
The seat backs have a surprising number of parts. The main seat back is just a thin corrugated sheet, so it needs to be stiffened up with aluminum angle - 2 thick pieces for the sides and 2 thinner pieces for the top and bottom. I started by cutting up raw stock for the side stiffeners.
The bottom of each side stiffener traps the hinge that mates up with the one riveted to the seat pan. I notched out just enough material so the hinge will fit between the stiffener and seat back.
To be able to adjust the angle of the seat, a brace gets attached to the upper portion of the seat back using a hinge. This movable brace slots into the different locations in the seat back bulkhead that I built a long time ago. I trimmed the pieces according to the plans and then drilled the optional lightening holes (no real reason - I suppose now I can carry two extra crackers because of the weight savings). I didn't have a hole saw the size called out in the plans, so I used a fly cutter at first. The first hole was fine, but cutting the second hole I really made a mess of things because the fly cutter wouldn't stay centered. The material is soft enough that the centering bit of the fly cutter was chewing away at the hole and making it oblong. So the fly cutter wandered pretty bad. I stopped and decided to finish up the holes with the largest hole saw I have. It's only 1/4" smaller, so is barely noticeable. I should have just started with the hole saw and left the fly cutter in the drawer.
I didn't take a picture of the fly cutter damage. This part is non-structural, so I just mixed up a little JB Weld that I had and filled the stray gouges. Once it set up, I sanded it smooth the next day.
All of the hinges and stiffeners cut and ready for holes to be drilled:
The top of the seat has a lip with an angle stiffener that nests inside of it. A few inches below that is the hinge that connects the moveable brace. The bottom of the seat also has an angle stiffener.
The moveable brace:
I deburred all of the parts and added them to the pile to be primed.
With the seats done, next up is the forward tunnel cover.
The tunnel cover supports are made out of extruded Z angle with lots of angles cut into them. I laid out and made the left side and called it for the weekend.
