Flyin' Bryan's RV-8 Adventure: Finally working with metal again

Thursday, April 13, 2017

Finally working with metal again

The tasks at hand as elaborated on in my previous post are to

Trim the ends of the top and bottom 408-1-L rib flanges to allow clearance for the shop head of the rivet that will fill that last pre-drilled rib hole in the skin

Drill the new rivet holes in the top and bottom of the LE skin a little further up from the above-referenced holes

Assemble the LE on the wing (fully clecoed) and match drill the new holes through the top and bottom flanges of the 408 rib.

Well, after thinking about this for the hundredth time, I realized that I might need to allow some additional room for the shop head of the rivet, and then I also realized that I will probably be drilling and riveting through my "sub skin" since it will be riding on top of both inboard rib flanges. SO those final holes in the skin will actually be attaching the Le skin to the subskin, but not to a rib flange. SO they won't just be hole-filling rivets after all.

The math for the clearance allowance for the shop head of the AN426AD3 3/32 flush rivets is 1.5 x the diameter of the rivet shaft. So if the rivet is 3/32 inches wide, 1.5 x that diameter is 4.5/32nds, or just over 1/8th of an inch. ( I hate using decimal values to the thousandth measurement, so I do it this way. To each their own.) To make sure the rib flange will clear the shop head of that rivet, I needed to adjust the location of the hole in the skin by about another 1/16th of an inch.

This is why you think about this stuff a million times, then you measure more than twice, and then you drill or cut as needed, and hope you did steps one and two correctly for you got to step 3.

Here is the first pics showing the new cutline raised about 1/16th of an inch on the rib flanges

The other thing that I realized is that by raising the cut line of the flanges, I also needed to raise the radius hole that will provide a smooth transition between the small portion of the rib flange that I am not cutting and the new "end" of the rib flange after I finish trimming them up. So I used my tapered round needle file to slowly move the hole up to the new corner of the flange to provide the radius for the corner that was originally going to be established by the original rivet hole.

This next pic came out dark but clearly shows the change to the hole that provides the radius for the flange as applied by the file:

I'll remove the rib from the wing spar and then use my Dremel cutoff wheel to carefully trim off the metal from both rib flanges. Once that is done there will be enough clearance for the shop head of the rivet so that it does not rub or interfere with the rib flange.

Next we move on to the LE skins and remarking for the new rivet hole location about 1/16th inch higher than the previous one. Then I had to figure out how I was going to drill the holes in the LE skin without having it mounted to the wing spar. I don't have very good luck with curved surfaces (See my posts when I tried to rivet the left skin for the HS. First rivet was OK. Second rivet was disaster. Without it installed on the wing the open skin is quite flimsy. I cant put the rib in there because the rib does not get drilled until the LE is attached solidly to the wing.

SO I came up with a solution by setting it upright on my table and using a couple of wood blocks on the inside and outside of the skin to keep it from moving. Since the skin is curved and not quite flat, I also put some shims in front of the inner wood block so that the skin has some support and the drill bit has something to bite into on the back side without distorting the skin too much. Notice the new drill hole mark about 1/16th inch higher than the previous one, to compensate for the additional rib flange material that I have to remove.