This evening I countersunk all the firewall gussets and stiffeners.

Next step was to start dimpling the firewall. I be darned if I didn't have the dimple dies in to make backwards dimples when I started. Oh well, at least it was only one dimple that I had to redimple the correct direction.

After dimpling all the rest of the firewall, I noticed these two rows of five holes at the top. The instructions don't say anything about them at this point, but I thought it would be a good idea to find the mating parts and match drill now so I could dimple the firewall using the c-frame. Should be much easier than trying to dimple when it's on the plane.

I spent a while looking for F-7107-L and F-7107-R. Couldn't find them anywhere.

Finally I looked at the title block of the drawing. Dang! This is the wrong drawing. I'm building a tip-up, not a slider.

Flipping one more page over, I determined the parts I really needed were F-745-L and F-745-R.

I quickly located those ribs, clecoed them in place and match drilled.

Then 10 more whacks with the hammer and I had those holes dimpled too.

Then it was on to dimpling the firewall recess flanges.

Here you can see how the dimples came out for those holes that were elongated. The dimple just barely reaches to the edge of the oblong hole. Cool. Once there's a flush head rivet in there, nobody's ever gonna know. :-)

Match drilling those ribs to the firewall this evening got me wondering what other items could (should?) be drilled to the firewall when it's a standalone piece of metal. I did some flipping through the drawings and found a few items already. The battery mount is one. The engine control cables pass-through holes is another. I'm sure there are more. Tomorrow I'll spend some time poring over the drawings to do as much work as possible before riveting the firewall together.