Well here's a f-up I perpetrated on my airplane today. We were countersinking and dimpling stuff today and I countersunk the wrong parts. These are the F-704C & D vertical arms of the main spar carry through bulkhead. I had forgotten about the F-704H doubler plate which gets sandwiched between these and the F-770 side skins, so I thought these needed countersunk. I got through three of them before realizing I had screwed up. So I went upstairs and called Van's to discuss it. Tom was quite helpful. He suggested opening the holes up to #40. This would eliminate much of the countersink, and the doubler is thick enough to countersink for AN426AD4 rivets. Good fix to a stupid mistake.

Here are two of the vertical members after being drilled to #30. The one on the left didn't get countersunk. The one on the right did and still shows some of the countersink, but it's better than before. The 1/8 rivets will be even stronger than the AN426AD3 rivets which were originally called out here, so strength won't be an issue.

After match drilling, I countersunk the F-704H doublers. I'm glad this wasn't worse than it was.