Saturday, October 31, 2009

Riveting battle won, the war proceeds apace

A comment from Wingman Ted on the topic of the ever-bending rivets stated the following:

As for your AD4 rivet, make sure you are using the right length rivet. From the picture it looks too long. When a rivet is too length it bends!

This is true, and I remember it from the sheetmetal class that I took at the local A&P school. But.... how could the rivet be too long when the rivet gauge borrowed from Co-pilot Rick indicated that the rivet was, if anything, too short? Sure, Van's warns us in section 5 of the manual that there will be cases where a too long rivet is called out in the plans and may need to be shortened, but... the rivet gauge! How could it be wrong??

Well, as it turns out, thusly:

Used that way, the rivet appears much too short. This is a sample photo taken later with a different size rivet and different thickness of metal, though - with the rivet in question, the error was not nearly as obvious. That said, here's how the gauge is supposed to be used:

Makes all the difference!! I didn't find that out until later, though. Still working under the impression that the rivet was bending because I couldn't get the squeezer situated correctly due to interference from the flange, I hauled everything up to the hangar and pulled out my Gucci rivet gun:

Would you guess that it hasn't seen much use in the last couple of years? Yep, both the rivet gun and me were pretty rusty - I drove a couple of practice rivets in a piece of scrap to remind myself how to do it. Then I aligned everything on the problem rivet, gave it a few shots with the rivet gun, and.....

bent it.

Drat. Having exhausted my limited knowledge without any commensurate gain, I contacted Co-pilot Rick for assistance. I loaded everything back into the car and hauled it up to his shop where he tried to drive a straight rivet. It bent. "Ah," he said, " it's too long."

"Impossible," I replied, "I checked it with the gauge."

You can guess how it went from there.

We used the bench grinder to shave a little length off of one of the rivets and Rick was able to drive it in perfectly straight. Only to find a completely new problem: a gap was created between the rib and the spar. That poor little rib by then had something like the fifth rivet drilled out of it. The newest problem was caused by trying to form the shop head (the part of the rivet that gets "shrunk" to form the grip) on the very thin metal of the rib. I was doing it that way because the manufactured head (the pretty one that doesn't get all squatted down by being riveted) on the side of the metal that would be visible to the outside world. Pure vanity, that, and completely unnecessary. Turning it around and driving with the shop head on the thicker metal worked perfectly. Rick pounded in all four and I headed back to Schmetterling to do the rest. Those were all squeezable because the called out rivets were exactly the correct length.

You can see the shop heads running down the row between the hinge brackets. Please don't look to closely; one of them is pretty ugly. It'll look nice on the inside where no one can see it, though:

The next step is to create a special rib for the bottom of the rudder. This rib will get riveted onto the big welded control horn/hinge bracket. For that to work, the front flange needs to be cut off:

That rib gets attached using a combination of the #4 solid rivets and a couple of blind rivets. I did the blind rivets first:

That whole deal gets riveted onto the spar with eight solid rivets. I was only able to squeeze six; the other two will have to be driven because of interference with flanges and such that precludes getting a straight shot with the squeezer. Well, that and because I insist on successfully driving a rivet by myself.

Tomorrow the rudder skin will go on, so I went ahead and deburred the remaining three ribs and clecoed them into place:

With a few more minutes before I needed to start preparing dinner, I also pulled the blue skin off of the rudder skin.

I worry that the heated language used while doing this puts me in danger of a deadly no-knock raid from the DEA, (they reportedly use thermal imaging spy cameras to detect the heat of the plant lights used for illicit basement farming) so to distract myself I thought about a fun prank I'd like to pull. A fellow brand-new-to-the-whole-game RV-12 builder asked on an internet forum what he should do about primer. The evangelists came flying out of the woodwork like those flying monkeys in the Wizard of Oz, of course, each having exclusive possession of the only possible right thing to do. I got to wondering what would happen if I replied to his question by saying that my plan is to just leave the blue vinyl skin in place on the inside skins, figuring it was put on there to protect the metal, right?

Oh, that would be a riot!


Torsten said...

Thanks, Dave, for the very detailed notes on the rivet length problem and how to avoid deforming the rib holes when setting them. This saved me a bunch of frustration and time. As you seem to be reading the Oregonian manual just as I do (meaning, I'm running into the same problems as you), I am now reading your blog entries BEFORE I work on a section to see what I have to look out for. Your blog is just priceless!

Vieille Burette said...

I really appreciated your detailed documentation of Page 07-04, not the least because I made the same mistake on the positioning of the Manufactured head on the rib (and for the same reason!) This taught me a lesson: read what Schmetterling did first! This also convinced me to organize my blog by Van's Manual page number as you did: it's the best way to be helpful for future builders.

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