I was now ready to begin drilling the aft fuselage. I started from the back and worked my way forward. Soon enough, I stumbled across and interesting hurdle. After batch drilling the bottom of the F-711 bulkhead you will notice that the holes are not centered in the tab, in fact they have a tenancy to be fairly close to the bulkhead web. I began to worry a bit about how I was going to work in this area for dimpling. I'll spare you the drama but basically after looking into things, it appears from what little pictures people actually post of this area on their build logs, many seem to have similar situations. I discussed the matter a lot with my buddy Mike and researched heavily into the option of countersinking the 0.040" F-779 skin as that will prevent the need for dimpling the tab which I was concerned with. In the end I decided against it. The manual states that it is common to countersink for rivets in material thicker than 0.040". When I first read it I missed the 'thicker than'. So I was seriously contemplating it. I double checked the head thickness of an AN426AD3 and its not all that less than 0.040". Also considering that I have to countersink the curved aluminum skin....the changes of a knife edged hole become extremely likely. Hence in the end I decided to dimple.
I unclecoed the F-712 and F-711 bulkheads to have a better look at what I was dealing with. In this picture it looks a little better.
I took out my Cleveland tool 3/32" close quarter die and ground it down a little on one side. I was then able with the help of bending the back tab a bit I was able to dimple the holes with the pneumatic squeezer.
