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aeropunk

Active Member
Dad and I are working on Practice Kit #2, this time in the home shop with my own tools. (Kit #1 was at a SportAir workshop.) We've run into a problem of "clinched" rivets (I think this is the terminology) while joining the rib flanges to the spar. By "clinched," I mean that while driving the rivet, some of it is "oozing" out between the layers of aluminum.

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(Click on the photo to go to Flickr and see my notes.)

Now, supposedly this is due to lack of deburring, etc., but we did this. No matter how well we clamped these layers together, they'd always spread apart while squeezing a rivet. What's going on here?
 
Hi Brian--

I was going to suggest clamping everything together tighter (new clecoes?), but then I saw the end of your post.

The other thing I can think of is to be sure you have pressure on the manufactured head before you begin the squeezer stroke. That may help keep everything together better.

I would also not skip more than one hole between rivets; IOW rivet every other one.

Other than those three, I can't think of anything...sorry.

Joe
 
In a situation like in your picture, I'd suggest doing the inside holes first and working outward. It's kind of like smoothing out wrinkles on a bed. You work from the inside out.

I have also on occasion used a dab of Proseal to keep two surfaces together when I couldn't get enough clamping power in the area. Like on those tabs at the end of ribs that are separated from the rest of the flange. Put a little Proseal on the surfaces, cleco them together and let it sit overnight.
 
There is a link...

..on this site some where that directs you to the Mil Spec for setting solid rivets. It covers things like shop head tolerances and allowable gaps etc.

As a general rule of thumb the "factory head" of the rivet should go against the thinnest sheet being riveted. Mind you it's not always possible for a multitude of practical reasons but it's a good goal.

This way the rivet set is pushing on the head of the rivet and forcing the thinner sheet against the heavier one thus tending to close the gap as the "shop head" or rivet tail is formed.

Some people use rubber "washers" cut from hose over the rivet tail, especially when using a squeezer. This compresses with the rivet and forces the sheets together as the rivet is set but in most cases you can use your fingers.

In any case for thin sheets it is good practice to minimally squeeze or at least not over squeeze the rivets since this tends to lead to sheet distortion.

Jim Sharkey
RV6 - Phase 1
 
air gun

Wherever I can get access, I use the air gun with a bucking bar opposed to the squeezer. To me its a hassle to keep up with resetting the squeezer and sometimes the squeezer is hard to hold down good and solid. I would try clamping the piece in a vice, and using good amount of force on the factory head and a lite touch with the bucking bar, drive those rivets working from the center to the edge. If these are flush heads, you might even can use the back rivet set. I dont believe it will ooze out like that.
 
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aeropunk said:
By "clinched," I mean that while driving the rivet, some of it is "oozing" out between the layers of aluminum.
Click to expand...
This could be caused by an underbent rib flange (less than 90 degrees). When clecoed together and held square to the spar in other ways, it may appear flush from the edge, but may not be sitting flush against the spar. You can check for this by looking into the hole before putting in the rivet - do you see a gap between the two sheets?

This happened to me between the rear spar and tib ribs of the horizontal stabilizer. Van's said it's OK and often unavoidable.

Boris
 
Thanks everybody for your ideas. To the folks who said, "Don't skip over holes," I agree with you. I think those middle two holes need rivets, but for whatever reason, the practice kit plans say that those holes are "ignored," i.e., not used. They're pre-punched, but you never match drill them, nor do the plans call for any rivets in them. I'm not sure why they're even there in the first place, but I bet slamming a couple of -4 rivets in them would bring that gap right down. Maybe it's more of a design issue in this case than user error, but I'm still inclined to suspect the latter. :p
 
We used to use a thick piece of rubber with a hole punched in it to go over the rivet. We would start to "shoot" the rivet then remove the rubber and complete the shooting. This would draw the two pieces of aluminum very tightly together before the rivet swells as a result of shooting.:)
 
Rivet Gap

Hi Brian.

I'm not sure that what you have is a "clinched" rivet. To me, a clinched rivet is one where the rivet tail has tipped over as you set it. You didn't say how you set the rivet, but I'm guessing a pneumatic squeezer?

I also built two practice kits. The first at Synergy Air. On that one those two rivets turned out well, and they were set with a CAT Main Squeeze. The second one I did in my shop and used a pneumatic squeezer. I had a bit of a gap form on those. Looking at it now, I think it is acceptable, but I would have preferred it to have no gap.

Flash forward to working on the RV9 HS. In trying to rivet the inboard ribs to the spar I had gaps. I probably drilled those rivets out three times. I clamped, I cussed, and I researched. The books I checked said that it would do that if the hole was too big. Another book said it would do that if the hole was too small. On the third try I got fair results and called it good. I had a two time RV builder look at it and his advice was "build on". Those particular rivets needed the gun and bar to set. Very frustrating.

I have since bought an Avery hand squeezer and seem to have better luck using it to set #4 rivets where a squeezer can be used. There is more control and things happen slower.
 
Denase said:
We used to use a thick piece of rubber with a hole punched in it to go over the rivet. We would start to "shoot" the rivet then remove the rubber and complete the shooting. This would draw the two pieces of aluminum very tightly together before the rivet swells as a result of shooting.:)
Click to expand...

Out of interest, what kind of thickness did you find works best. I suppose this will be also a function of how compressible the rubber is ?
 
Welcome to the world of sheetmetal.

Lot's of good suggestions on how to help this. To be honest, when working with thin sheet (<.032) you are gonna get gaps and shanked rivets. (rivet set so that you can reach it with a feeler gauge between sheets). Back riveting helps, driving the head on the "thinnest side" also you can use a "draw" technique.

To "draw" takes some real finesse and you use low air pressure.

1. Drive the rivet just a little bit (till it is just barely swollen)
2. Place your bar next to the rivet shank and tap until the gap closes up.
3. Drive it the rest of the way.
 
What thickness I am not sure, I do remember the neoprene being just thick enough to be even with the top of the rivet before shooting. So you would use slightly thinner material for a number three than a number four or five rivet. The donut also worked when we used a phnuematic squeezer. Looking on a website this am I found a company that sells samples of neoprene cheap. Comes in .063, .092, .125, and heavier. There are alot of guides to tell you how high and wide the finished rivet side should be, but not how much rivet shank should be exposed before shooting.:)
 
Just curious. In the early 80's I worked at the old FRONTIER airlines where I was involved with the replacement of entire belly skins, on a 737 due to corrosion. We used the donut technique to drive all the rivets. Has no one else on this forum heard of this?:confused:
 
Use RC airplane fuel line

I use RC airplane fuel line for my "donuts" I think I got this idea from someones build page. I slice off a bunch of these "cushions" from a length of fuel line at a time, as the riveting with destroy a cushion after a dozen rivets or so. I cut the cushion slightly longer than the rivet tail so that the bucking bar will compress the cushion enough to touch the tail of the rivet without requiring excessive force on the bucking bar. If I am having a problem getting the flange to lay flat on its mating surface I will cut a longer cushion. I usually just drive the rivet in one shot and then remove the cushion. I have used this cushion technique on every one of my rivet gun driven rivets except for the fuel tanks. This works pretty good, but after reading others posts on this subject I am going to try the sheet of neoprene technique and see if that works better for drawing flanges tight.
 
Old trick

Hit the rivet a couple of taps to start it to swell. Then lay the bar next to the swollen tail and against the sheet and tap it a couple of more times lightly (very). This will bring the two sheets together. Because the rivet is swelled, everything will stay together when you go back finish driving the rivet. I was tought this in A&P school in 1970 and have used it ever since. Much faster that messing with donuts etc.;)
 
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