Ready to Rivet! 5.5/146 hours

Well, during the month of February I've managed to fit, trim and drill the left side HS skin (8 hrs), deburr both skins and the skeleton  (2 hrs), set up the DRDT-2 dimpler and repair one of its supplemental tables that we broke during the move (1.5 hrs),  dimple the skins (2 hrs), and today, dimple the skeleton (5.5).

I owe a lot to the guys on Vans Air Force (VAF) for information on how to properly set up the modern, beautiful, lever-action DRDT-2. I've used it before on my first start at an airplane project, the CX-4. (I was building it with dimpled, flush rivets and using the RV-3 instruction manual to figure out how to build it, so I switched over to the real RV-3 last summer.) Anyway, my CX-4 rudder skin had slightly dished-out dimples, which made the rivets hard to buck without denting the skins and leaving the rivets slightly proud. After examining a P-51 last year at Oshkosh closer than I ever had before, I realized that properly set flush rivets should be exactly that, "flush!" I wondered why my dimples weren't as perfect as the Mustang's. Possum, my tech counselor, said he didn't like the DRDT-2. He preferred the old-school C-Frame, and said that you had to pound each dimple twice on the C-frame to make a perfect dimple. His plane has perfect Lindy-winning dimples, so I couldnt' really argue. Some guys on VAF said the same thing, but others said all you need to do is "preload' the DRDT-2 dimpler to put extra pressure on the skin. Ben has had it for a while, he paid good money for it, and I remember what it was like to pound dimples with a C-frame and a hammer when we built the RV-10 tail. It was loud, jarring work and it was easy to damage skins with a misplaced blow. I love the silent, easy motion of the DRDT-2... so I was very thankful to find out that there is hope for good dimples with it, after all.

You set it up so that the dimple dies touch each other when the lever is all the way down. Then, you crank them together an extra 3/4 turn. This places a lot of pressure on the dies so that it deforms the metal fully according to the shape of the dies. I made up a test strip with 4 holes. The first hole had zero preload, and it looked dishy, similar to the CX4 rudder skin-- which made sense, since I did not set any preload when I dimpled the CX4 skins. The last hole had 3/4 turn, and it was crisp. There was no distortion of the skin outside the immediate area of the dimple. The rivet sat slightly below the surface of the skin, but when I squeezed a test, the rivet came out flush and not proud. Excellent! (Photos will come when i get back to work and upload them off the other camera chip...)

After figuring out the DRDT-2 (without any help from the man, by the way, who was even slightly offended that I would consider his dimple-machine inferior,) and making the best dimples I could have dreamed of in the skins, how hard could it be to make dimples in the skeleton itself?

This was NOT a good way to start!  SHIT!! It was like piercing an ear. As I tried to wriggle the pneumatic squeezer into position on the end of the spar, I prematurely bumped the lever. The alligator pressed the dimple die right through the spar flange just OUTSIDE the hole, which you can see just above the die. D'OH! I was just glad it's not in a place to worry about structural strength. It isn't pretty but it won't cause the tail to fall off, since it's on the tip.

I removed the die and gave use of the pneumatic dimpler some additional thought... The jaws are really too big and awkward for these parts. And obviously, a mistake in placement of the dimple die will go unforgiven. So, I switched to the smaller hand squeezer. Ben ground the nose of the yoke flat a long time ago, during construction of the RV-10 tail, for dimpling holes close to spar webs-- which is what I need on this piece, since the spar doublers and rivet shop heads are very close to the rivet line. I continued up the spar line with the hand squeezer... oww... I have little bitch-hands with zero muscle mass, so this hurt, but I got them all done. To make sure the dimples were deep enough, I periodically checked them against a piece of .032 scrap with a dimple made by the DRDT-2 and the Cleaveland dies, and made sure it sat flat inside the skeleton dimple. There were several holes that were too close to the elevator hinges to dimple, so I countersunk those using the same scrap dimple gauge to check depth. 

I put on some fuzzy blue gloves to prevent blisters on my hands during the second half of the skeleton-dimpling operation. It worked!

What did I do with the extra-hole monstrosity? I dimpled the "real" hole, which flattened the punched hole, and I will drive an OOPS rivet in there. I'll secure it with a drop of epoxy to keep the rivet from working loose, since the hole is not quite round anymore, and a bit bigger than the 1/8" OOPS rivet will fill. Something to put on the list of anomolies to check during each annual inspection, I suppose... I am glad that it's easily accessible, in case it works loose in the future.