February 2, 2007

Prep Work on the HS Skins - 6.0 Hrs.

With all the ribs and internal parts dimpled and ready for priming, today I set out to finish the prep work on the skins. That means making sure all the edges of the skins are deburred and smoothed first. Next, I pulled the blue vinyl off the insides of the skins and used my soldering iron to cut thin strips off the rivet lines on the exterior sides. Then the skins are dimpled. I set up the dimpler and dimpled both skins.

I took a few pictures at this point, because I'm not happy with what I'm seeing with these dimples.

See those huge craters, or depressions around each dimple? This doesn't look good at all, and I don't know what I'm doing wrong. I'm so disappointed. I wonder if there's something wrong with my dimpling tool, or my dimple dies, or my technique. I think it's time to call my technical counselor for a visit and see if he can help me figure this out.

In the meantime before he could come, I thought of something that might help. I took the female side of the dimple die set and a handful of rivets, and set the skin on the bench, exterior side down, with the rivets sticking up through the holes.

My idea is to put the die down over a rivet, and smack it with a hammer. Hopefully this will flatten things out a bit and improve the appearance of the dimple.

I did this and noticed some immediate improvement.

I did a whole bunch of these and then turned it over to check the results.

Wow! Much better. Still not real crisp and sharp, though.

But let me cut to the chase here. Shortly after this point, my technical counselor at the time, Randy Lervold, came over to pay me a visit. Randy is well known among RV circles, having built both a finished RV-8 and a stunning RV-3, and other projects (there's a link to one of his sites on my Home page). I don't know anyone in the world as knowledgeable as him. I was excited to show him my new DRDT-2 dimpler, thinking he would really be impressed with this new tool that I knew he didn't have. He did all his dimpling the old-fashioned way with a C-frame and a hammer. Boy, was I wrong. He was not impressed at all. He immediately saw that all my skins were under-dimpled. And he blamed the tool at first. He had paid a visit, he said, to a number of new guys like me and saw under-dimpling with all of them, particularly when they had a DRDT-2 dimpler in the shop. Under-dimpling is a common thing, apparently, with new builders. Randy is old school, and much prefers his C-frame to my fancy new dimpling tool. I couldn't argue with the results. His dimples were beautiful, crisp and sharp, and the finished rivets nice and flat.

So before he left, I knew I needed to go over to his place to see his C-frame, which I later did, and learn how he dimples his parts and do some comparisons. It was fun watching him practice on some scrap, and I learned a lot. I was definitely under-dimpling. He would smack each dimple hard with the hammer twice. Once to create the dimple, and the second time to really smack it hard and shape it to a good crisp finish. It leaves the surrounding metal perfectly flat. And let me tell you, his rivets are gorgeous. There's an old saying out there: don't be shy or timid. Beat that aluminum into submission.

So later, I set about to see if I could improve the dimples from the DRDT-2. I learned that if I adjusted the ram down some more, and locked it in place in a more extended position, it would work much better. I set it so it contacts the metal well before the arm is pulled all the way down. It ends up using so much force, you can actually see the big steel arms on my dimpler flex and bend apart a little bit under the force. And I hit each dimple twice with it, just like he did on the C-frame. From this point on, my dimples look really good. I'm not totally happy with the dimples in my Horizontal Stabilizer, but it is acceptable. I already had the HS skins riveted on before all this took place. I'm not going to rebuild it, and I'm not going to drill out all those rivets either. But if I were to do it again, it would have a much nicer appearance.

Later on when I was building the wings, I found an almost-brand-new C-frame dimpler for sale on eBay for about half the price of a new one. So I bought it. The only thing wrong with it was that it had a tiny bit of paint spilled on it. A little bit of MEK took it right off, and it looks brand new. From that point on, I used the C-frame on all the exterior rivets where it really shows. The difference is very subtle, but I do think the C-frame gives superior results. Sorry, but I have to go with the old-school guys on this one.

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