The Theme for Today was.....More Dimpling of WIng Skins and Ribs

Yesterday I had managed to go as far as I could with the top outer left wing skin panel as far as dimpling is concerned. As previously posted (I think) I missed match drilling two holes. I could have taken an easier path by just independently drilling the hole in the skin and rib/rear spar, but as any of you following my blog have already surmised, doing things the easy way is not my forte. SO I needed to match drill these two holes, which meant putting the outer skin panel back on the frame, match drilling the missing holes, and then removing the skin again to debur the holes properly and dimple them.

SO I did just that today. Since this was the first time I mounted the skin to the ribs and the spar with the dimples and countersunk holes in place, I was able to check the fit as I reclecoed the holes. At first there was some misalignment of all holes on the inboard edge for some reason, but using a graduated approach to clecoing the holes, and they managed to align themselves pretty well.

Once this was done, I we to check the fit of the skins to the ribs and the spar with the dimples. I was pretty happy with the dimple-to-dimple fit of the skins to the rib flanges, but the ft of the dimples to the countersunk holes in the spar is another story. I don't seem to be able to use a "test" dimple on some short piece of aluminum very well. I just can't tell if it actually fits. The problem is that trying to verify the fit of something on the wing spar flange is difficult for me because the flange is bent, and there is only a small portion of the test piece that rests on the small flat part of the spar flange I cannot tell if the test dimple and the metal surrounding it are actually fitting correctly, because if I apply a little pressure to it it seems to end up flush with the spar.

Other folks with videos of this always show some test dimple and a another "test" piece of aluminum, but they never show the test piece up against the actual part, such as a wing spar flange. I find this to be troublesome. Are you supposed to have a little spring back with the dimple in the countersunk hole, or none. I do know that if the countersunk hole is too deep, you risk denting the skin as you rivet it, which causes other major problems. SO you definitely do not want to end up doing that.

Anyway, the edge of the skin where the dimple fits into the countersunk holes of my wing spar appear to be "pillowing" just a bit when clecoed. this is a sign that the countersunk hole may not be deep enough for the dimples.  This will become even more pronounced once you try to rivet these holes. MY problem is that the pillowing seems to be evident in between clecoes as shown the next pics:

However, if I put clecoes in every hole, they seem to tighten up. I watched some videos of other builders today who demonstrated that if you are placing a dimple in a countersunk hole you have to enlarge the countersunk hole quite a bit to allow the dimple to rest in the hole properly. In fact, from the examples I saw, it looked like it took 1/32 of an inch more depth to make it fit properly for a dimple, as measured by the exposed metal at the top of the hole if you put an AN426AN- 3 rivet  in the hole.

Then you can take a caliper and measure the width of the dimple and the hole and compare them to see if the edges of the dimple should fit inside the the countersunk hole. The last time I had to deal with this, and frankly I am about to find out if I did it right back then, was when I was countersinking the holes for the #8 nutplates and screws in the wing spar for the fuel tank. That was a long time ago, and it was not for any 3/32 holes that would be receiving a dimpled skin. SO this feels like some new territory.

Sounds like I have some more tests to run to see if I need to enlarge my countersunk holes a bit more or not. Anyway, with that first fit completed, it was time to remove the inboard wing skin and debur and dimple it AND the wing walk doubler, which I have not laid my eyes on for a very long time. I removed that skin and proceeded with checking the holes again and deburring them again as necessary, and filed those bumps on the edges, then deburred the edges, rounded off the corners, formed the small bend in the skin edges, and dimpled as many holes as I could reach with the pneumatic squeezer.

I also did some math to try to figure out how much material in each wing skin I need to remove to scarf the joint that sits next to the fuel tank skin where the inner and outer wing skin panels overlap. I need to get some attachments for some sanding disks for my die grinder tomorrow at Harbor Freight so I can complete that little fabrications exercise.

Here is the inner skin on the dimpling table. Since this skin section is smaller than the outer one, it was much easier to maneuver and flip this skin panel on the work bench. I also took a pic of the partially dimpled wing walk doubler.

Tomorrow I finish dimpling the holes I could not reach with the squeezer, scarfing the corner of the inner and outer wing skins, and then it will be time for final edge prep, then scuffing, cleaning and priming all the interior portions of the skins and the wing walk doubler.

Mainly I wanted to get to a point where I can remount both dimpled wing skins to the frame and then mount the LE again to layout the pattern for the cuts in the outer skin. That was the original part of the plan several days ago.

Winter arrives tomorrow night and into Monday, but it looks like things recover for the rest of the week.I'm getting closer to some major assembly steps and actually slamming some rivets.