Fitting the firewall^3h

Mustered my will, and drilled the firewall to the skins today!

During the last few days I was fitting the firewall. Measuring, clamping, measuring again, the clamping some more. The idea is to get the firewall forward/aft to be 5/8" from the edges of the skin. Forward/aft because instructions say "forward face of the firewall", but the plans show "to aft face of firewall". After some research, it seems that small variability is not critical here.

I don't think I got it perfect, but I did get some alignment, and finally, drilled the holes.

First, the side holes attaching the firewall flange.

Then the bottom skin to the firewall flange and the angle.

Finally, I drilled the holes in the steel engine mounts.

I drilled them with the #41 drill bit first, then upsized them to the #30. Since the holes in the longerons and the skins were already drilled to #30, I used a small brass tubing as a drill bushing. Then I used a couple of more drill bits to upsize the hole, and finally, the #30 reamer.

Managed to break a couple of drill bits again. It seems like what works is to use multiple drill bits to upsize the hole, if a drill bit is too large, it grabs and breaks. Oh well. The holes look okay. A couple of them are less than perfect but will see in the end. If I did mess them up, there is still an option to upsize them for the NAS1241 rivets.

This is what it looks like from the inside.