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Elevator stiffener riveting - back-rivet never worked right.

tegwilym

Active Member
Anyone else have this same problem? I was back-riveting the stiffeners onto my elevator skins, and they -always- bent over a little bit. I didn't have this problem at all with the rudder skin/stiffeners, but then of course that skin was thinner and rivets shorter. That worked out very well.
I tried removing a few of the worst ones, and basically ended up with an uglier hole. I drilled it to #30 and used a -4 rivet in there instead (next size up method).
The elevator was a different story. They just never could go in without leaning or "smearing?" over to the side. Some reason it always leaned toward the leading edge. I was using the backing plate and the spring loaded rivet bit too.

I then tried reversing and simply clekoing the stiffeners with every other hole, and riveting with the "red rubber mushroom" riveter attachment on the skin side and the buck bar on the inside. That all worked out very nicely on the shop side and the factory head worked flush too. I did have a few to remove and re-do, but they turned out pretty well.

Is there any drawback to have done it this way? It seems that my flush heads are in pretty well, and not sure if I would have any more indentation around the skin if I did it correctly with the back-rivet way.

Anyway, just looking for some reassurance that diverting from the plans isn't a problem.

Tom

1236969_10201371665110244_1565170530_n.jpg
 
The back rivet set requires quite a bit more air pressure than the mushroom set. Every time I have had issues with rivets not setting properly, I have the wrong pressure set (either too low or too high).
 
It seems that no matter how much or how little pressure I used when back riveting they would always move over to one side. I would try with a very light squeeze and gently tap them in and it would still end up crooked, and when I tried a big blast they would certainly go crooked!

It was almost as if the rivets were too tall but they appeared to be about the right size.
 
It seems that no matter how much or how little pressure I used when back riveting they would always move over to one side.

Perhaps a problem with that particular spring-loaded set? I'd try another one. For me, back riveting has definitely proven to be the easiest method for getting consistently excellent results.

--
Stephen
 
When using the flush or mushroom rivet set it is easier visually to set everything square. The rivet gun is flush against the skin and although the bucking bar is covering the shop end, you can set it up perpendicular to the skin visually as well.

The back rivet set covers the rivet and as you look down at your project it is much more difficult to set it square to the shop end. You can not really see it. Add to that the AN426AD3-3.5 rivets do not take much to set. So a few degrees off of square gets a malformed shop head.

There is nothing wrong using a bucking bar, but you can get really nice results back riveting. I think it is faster too. If you have some scrap, practice back riveting.

I know it is frustrating setting bad rivets. I have drilled out way too many rivets. I wish I had practiced more before starting my tail.
 
There is nothing wrong using a bucking bar, but you can get really nice results back riveting. I think it is faster too. If you have some scrap, practice back riveting.

I did get all my stiffeners set, and I think they look ok on the skin side (see photo above). Yes, it did take a lot longer with the "red rubber mushroom" riveter, but I got nearly perfect looking shop heads with it. None had the tendency to lean over. I think the "spring head" has to really be perfectly perpendicular. Now that I think of it, it may have been tipped slightly toward me every time since they leaned toward the leading edge (where I was standing). But even then, I tried very hard for a perpendicular setting, but just never worked. Anyway, I guess this is why they call it amateur kit building right? :D

Yes, I have also removed a lot of rivets, but find that the leaning rivets end up with nasty holes even when drilling them out straight!

Tom
 
shadow alignment

Using a light or two to cast shadows to show vertical alignment helps a lot. Not holding the gun square (or drill) is very common mistake for new sheet metal workers. The two light method will help you learn what the tool is supposed to look like from one angle.
 
I had the same problem. I bought a back rivet set with a plastic tip and shaved one side flat. The round set could not set square because of catching the bend in the stiffener. Just place the flat side against the bend and problem solved!
 
I had the same problem with my first back-rivet set. I got it at the Yard Store because I live close to it. In search of a solution to the problem I eventually bought the Avery back-rivet set. Problem gone.
 
I too ground one side of the plastic guard on the back rivet set down flat, so that it would fit on the stiffener. I also found that I had to angle the set slightly towards the vertical flange to end up with a good shop head. Don't know why, but it worked. Also, press down very firmly.
 
are you holding the sliding guide with your other hand? I did this to keep it on the the rivet better.
 
Good point Bret.
I think that goes for all sets, if you have that extra hand available via the use of a back rivet plate or a helper on the bucking bar.
 
skin stiffeners

I used a backing plate with the back rivet set ground flat on one side to clear the flange.
I suspect that may be the issue. The back rivet set is pressing against the flange causing the shop head to go to one side.
 
Did you use the recommended rivets (3-3's)?

A lot of builders use 3-3.5's because based on a rivet length gauge, the 3-3's look a little short.
The 3-3's are fine. There is a big difference in riveting difficulty if you switch to teh slightly longer rivet.
 
I have all my stiffeners in place and riveted. Today I riveted in the trim tab back plate. I tried again with the back riveting on this part. I held it straight, plastic ring down flat on the piece, held it with my other hand, and -gently- tapped the rivets in with light squeezes.
I tried three times and they all sucked!

Bucking bar in left hand, riveter with rubber "mushroom" in right hand. 20 minutes later they are all in nice and straight, none had to be removed either. The back plate just hates me I think.

Tom
 
You don't want to be too gentle with the gun, or you risk work-hardening the rivet before it's set. Maybe a long second or two, no more.

As others have said, most find back-riveting to be an easier way (than mushroom-bucking bar) to get satisfactory results. Take a good look at your back rivet set. Something just isn't right.
 
I had the same problem with my first back-rivet set. I got it at the Yard Store because I live close to it. In search of a solution to the problem I eventually bought the Avery back-rivet set. Problem gone.

Listen to Kurt. Where did you get your backrivet set? I also started with a set from the Yard, thinking I didn't need an expensive tool for this task and for some strange reason it wanted to tip the rivets. While back riveting seems like a no brainer, I have also struggled at times with it. A few weeks back I was talking to another local builder, a respected machinist, and he confessed he had also struggled with this at times.

The only backrivet set I own that provides consistent, good results is the set from Avery. It gives me a perfect rivet every time. Borrow another set and give it a try.
 
My back rivet set was from Cleveland tools. This one - http://www.cleavelandtool.com/Back-Rivet-Set/productinfo/RSB35/#.UjDqHSJDvSw

RSB35-Large.jpg


Like I mentioned, I did the whole rudder just fine, but the elevator absolutely refused to go straight. I tried several ways, straight, long/short burst, and it never went in right. I screwed up a few holes removing the bent rivet and enlarged them for the next size up to fit snugly and use that as a fix. Finally gave up and used the red rubber thing.

I'm just hoping I didn't mess anything up doing it that way, but it would have been more screwed up if I kept going the way I was. :(

Tom
 
I looked at an RV6 down at the airport yesterday and examined his elevator. It looked very flat. Mine looks like cr@p compared to that one!

here is about the worst of the rivets. I did do the elevator trailing edge bend and that went well, but then staring at this, I'm just getting more disgusted with how it looks. Maybe I'll replace the skin and stiffeners before going farther. Grrrr...!
Hey, the good thing is, I'll have plenty of scrap to practice backriveting on so I don't mess up the real thing! :rolleyes:

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Tom,

I had a problem just about like that on a previous project. As it turned out, my bench top wasn't stiff enough to react the blows of the gun, and the rivet heads ended up slightly proud, just enough to catch with your fingernail. I solved the problem by moving my backing plate and plywood with the cutout down to the concrete floor. You'll need knee pads or a cushion to kneel on but the results will be worth it.
 
So I initially had some trouble with my first back rivet set. It had a wider collar so it didn't fit well due to the bend of the flange on the stiffeners. As some have said before I guess you could grind down one side of the collar. I ended up buying a different set that had a thinner collar. I cant remember who it came from, either Cleaveland or Avery. With this set I was able to get the set in the correct position and keep it vertical while running the rivet gun. From one of your pictures it also looks like your backriveting plate isn't polished or something. At least one of the rivets shown has a rough head like it was driven onto an un-polished surface. I purchased a backrivet plate from Cleaveland and it seems to work.
 
how heavy is the plate

i use a piece of steel 7/8 inch thick by 4 inches by 10 inches with 3/4 inch wood around it for a table the gun has just a small flat set without any spring to hold the metal together i use my other hand with a finger on each side of the rivet pushing down
 
Replace and try again.

I have the Cleveland plate that is about 6x10 or something around that size. No, it's not polished. I guess that does leave a bit of dark stuff on the rivets, but that cleans off easily.

I've pretty much decided to ditch these skins and stiffeners and order new ones and try again. :( That will also give me a nice big chunk to practice on and figure out what I'm doing wrong, then try it.
Also, might try the Avery riveter this time also. I hear a lot of good things about that one.

I'm just not happy how this turned out, sure, it would probably fly fine, but it's just really not pretty at all. I figure that it will just take me a few days to get the stiffeners cut, drilled, dimpled and primed and ready to go again.
 
WOW! what a surprise

I went to the builders school at Vans in 1996 and one of the things we were taught was back riveting. I bought a one piece back rivet set which is several inches long (its out at the hangar or I would measure it - 6 to 10 inches is a guess) with a crook in the shank with the recessed head from Avery or Van's and never experienced any problem at all. I always practiced with scrap metal at the start of EVERY rivet session to get the pressure and the technique to an acceptable quality level before starting on the real work. Working with the steel back rivet surface plate and the back rivet set was a lower risk process than the common rivet set and bucking bar because of the forced flatness of the outer skin surface and the manufactured rivet head. When Jeanine and I riveted on the aft upper fuselage skins I got in the fuselage and used the back rivet set and she held a bucking bar on the manufactured head of the rivet outside the fuselage.

One thing I was taught at the school is rivets that are too long tend to clench so if they clench an alarm should go off that the rivet is probably too long. AND, if a rivet is clinched you can often do more damage by trying to remove it than leaving the slightly undesirable looking shop head in place and moving on to the next one.

A rivet cutter to modify rivet length before riveting works very well for me.

Bob Axsom
 
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I've pretty much decided to ditch these skins and stiffeners and order new ones and try again. :( That will also give me a nice big chunk to practice on and figure out what I'm doing wrong, then try it.
Also, might try the Avery riveter this time also. I hear a lot of good things about that one.

Another thought. I see you're local to me, how about getting together and we can see what's going on. Looks like you are in Renton, I'm just south in Auburn building an 8. Send me a PM with your contact info and lets meet up.
 
A lot of builders use 3-3.5's because based on a rivet length gauge, the 3-3's look a little short.
The 3-3's are fine. There is a big difference in riveting difficulty if you switch to teh slightly longer rivet.

Although you are getting a lot of advice, I would give what Scott says here a LOT of credence. After all, Scott builds prototype aircraft for Van's ( in case you didn't know)

I had the same problem with practice pieces. The rivet call out in the plans (especially the older model RV-6 plans) is a guide. Once I switched to the shorter rivet, problem gone. And yes, they may appear a tad short with a rivet gauge but are structurally just as strong. I'd rather use them then clench the longer ones.
 
Another thought. I see you're local to me, how about getting together and we can see what's going on. Looks like you are in Renton, I'm just south in Auburn building an 8. Send me a PM with your contact info and lets meet up.

Sure, I'll send it offline. Thanks!

Tom
 
polish

I polish anything that touches the manufactured head. Rivet sets and steel bucking bars and the back rivet plate are polished using 400 grit and oil on a steel plate so they are as flat and smooth as possible. It keeps from scratching even though I plan to paint. I also use book tape to protect the skin.
 
I just put in an order for new skins and stiffeners. $156 for the parts. Overall, that's not a bad price. I just tell myself - if this was for a Cessna, 't would cost a LOT more and I would have to hire an A&P to do this and pay the hourly wage.
I also put in an order for the Avery backrivet set for $30 since that seems to be a popular one from what I've read.

Now to remove a few stiffeners and practice to get these things right this time!
:p

Again, thanks for all the tips and advice. I don't know how we ever built airplanes without the internet!

Tom

---------------
RV7A
Renton, WA
Vertical stab - done
Horizontal stab - done
Rudder - 90%
Elevator - starting over! :D
 
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