It’s been a few days since I worked on the plane, but I’m back at it. The four vertical row of clecos will have to have the rivet holes countersunk. This area included the Top Inboard Skin, Wing Walk Doubler-AFT, and Wing Walk Doubler-FWD. The Top Inboard Skin is only .032, so the plans caution not to countersink two deeply. Additionally, under the three pieces mentioned above, is the Flanges of Wing Ribs #1 - #4. So the material is relatively thick considering....if you combined them together. But regardless, you have to be careful.
As I mentioned above, because the Inboard Top Skin is only .032 thick, the plans state that “under” countersinking by .005 is acceptable and a preferred method. As a result, the AN426AD3 rivets will not sit completely flush with the Skin. However, that is not a very big deal in this location. There will be wing walk affixed to this area once the plane is complete and will “hide” the slightly proud rivet heads. Below, you can see the .005 gauge I used to measure the depth of the countersink. The rivet is NOT set, but just sitting in the whole and used to show the comparison with the gauge.
To get the correct “undersink”??, I used my countersink cutter (with a #40 cutter) to make the countersink. I then held a 6” ruler vertically on top of the rivet head. Finally, I used the .005 gauge to check the gap between the bottom of the ruler and the top of the Skin. This worked out pretty well for what I was doing. I also used a razor blade in the same fashion as the ruler. Either seemed to worked great.
Kind of hard to see, but here is a picture of the very first countersink I made.
I have completed the countersinks required in the Top Skin that sits over the Wing Walk-FWD section. I will complete the Wing Walk-AFT section tomorrow and continue with the steps in the plans.