The construction manual has you tape off a set of holes that are not dimpled or counter sunk. The initial builders found errors in the holes that were called out and it took 2 revisions to the plans before the factory engineers got it right. I though I was staying on top of the changes, but I ended up countersinking too many of the holes in the F-1401D cross stiffener. I considered ordering a replacement but then I read more about what the first builders did. It turns out you can order conical washers to insert in the countersink. I didn't want to wait around for an order to arrive, plus the minimum order is for hundreds and I only need 4. So I made my own washers by carefully drilling out and filing down some counter sink rivets.
Here I've put the washers in the holes with a very small dab of ProSeal to hold them in place until I assemble the stiffener.
The instructions have you ProSeal the edges of the upper panel and center piece where they overlap the lower panels. You don't want carbon monoxide or hot gasses leaking through the firewall into the cabin and the ProSeal insures the integrity of these joints.
I back riveted all the rivets today. It took a lot of time and patience to line up the bucking plate/bar to work around all the edges of the overlapping pieces and the diagonal fluting. Complicating all this was the ProSeal oozing out and getting on everything.
I got most of the heavy riveting done today, but I still have to figure out how to get to the rivets around the nose gear brackets. The holes in the corners are for the bolts that secure the engine mount to the firewall. Lots of reinforcement layers and rivets to carry the engine loads.
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