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Rivets are bending over . . .

lsissom

lsissom

Active Member
My first VAF forum question.... (always have been able to use 'search' to find someone who's had the same issue until now)
The rivets that attach the 7A wing ribs to the front spar appear to be WAY too long. Van's calls out for AN470AD4-7 for all the ribs to the front spar. Thought it maybe my lousy technique... but they're bending consistently... I'm practicing on my scrap, and everything bends over. Using a 3x gun, tried changing air pressure, no difference.
Never had to use my rivet cutter before. Is this where I start cutting rivets?
Thanks for any response you may give.
 
I built an entire RV7A and never used my rivet cutter. Do you have a rivet length gage? Such as http://www.averytools.com/pc-1059-23-import-rivet-length-gauge.aspx ? Are you sure you are reading the plans correctly? -7 does seem way too long. Anyway, the rivet call out is just a starting point. Sometimes you have to adjust a little. It didn't happen often, but it did happen.

If they are bending over, they are too long.

One last thing YMMV, I found that 45# was a good starting point for AN470AD4 rivets. The thicker the material, the higher the pressure.
 
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You probably do, but...

Larry,
Do you have a rivet gauge? ...Used to check for correct rivet length.
 
this is embarrassing ... I have that little gauge... never used it.
I didnt realize it was for measuring rivets BEFORE setting.
But I'm thinking now it may be my technique with the larger/longer rivets thats the issue...
I calculated the "ideal" rivet length (material thickness + 1 1/2 X the rivet dia.) and I get .4105
the AN470AD4-7 is .443 so a little long...
the AN470AD4-6 is .380 so its less than the calculated ideal length
Right now I'm thinking the rivet length is not the issue . . . (more practice on scrap required)
 
I've never used a rivet gauge before riveting or rivet cutter at all. If I bent a rivet over, I usually double checked the plans to be sure the rivet callout was correct (quite often I misread). Fairly quickly on, you can just tell by looking at the amount of unformed shop head that's exposed to know whether it's the right one.

But check your bucking bar technique too. A lot of folks push against the rivet HARD. The bucking bar can't do its job that way. You're probably also exerting side pressure on it too. Try easing up on the pressure you're using on your bucking bar.

For now, also, just try a couple of short bursts as you set the rivet, check condition, then finish it up.
 
using my rivet gauge

I went out and used the rivet length gauge for the first time... and assuming I'm using it correctly, the N470AN4-7 rivets that the plans call out for appear to be the correct length.
So, I'll go out and work on my bucking bar technique, and experiment with different air pressures and guns (2X or 3X) ... It may be that using the 'squeezer' so much I've gotten rusty with rivet gun method.
Thanks everybody for your input.
 
AN470 4-7, pretty much anywhere or with any material thickness and a 3x gun, start shooting with about 70 pounds. The bucking bar should be firm and square with a nice long rivet gun pull, of 10 or so hits. That is for a short, 2" rivet set. Add another 5 pounds per inch of the rivet set if it is longer.

We had the same problem on the 9, and this fixed the problem for us. The process transferred to the 8 and worked like a charm.
 
Use the 3X gun. With the right gun you can feather the trigger so lightly that you can almost count the hits. Give it a real short burst, two to three hits. Now look at the rivet. If it is starting to lean then push it back with a little angle on the bar the other way with another short burst. Stop and look again, make the adjustment etc. Take is slow and it will work out. You can usually save all difficult rivets by using this method. After you get confidence your fingers will learn how to move the bar the right way as you set the rivet.
 
Gun size / air pressure / rivet size table?

thanks ... I appreciate the advice.
I like this idea of a specific amount of air pressure for specific application . . . until now Ive never changed the air pressure (set at 90#) but have used the fine adjustment on the tool to dial in less... trouble is I dont know what pressure I'm finally at.
I can see the wisdom a prescribed air pressure for a specific size rivet and maybe slightly adjusting later.
Is there a gun size / air pressure / rivet size table out there that I could use as a reference?
 
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lsissom said:
Ive never changed the air pressure (set at 90#) but have used the fine adjustment on the tool to dial in less... trouble is I dont know what pressure I'm finally at.
Click to expand...

90 pounds is way too much with a 3x gun. For AN4 rivets, I use 63 for the average rivet, and perhaps a SLIGHTLY larger amount for a longer rivet. For your typical AN3-X rivet, I use about 38 psi.

On his old Web site, Dan Checkoway offered these guidelines:

AN426 Rivets:

Rivet Type Air Pressure Duration
AN426AD3-3 to 3-4 34 psi 1 second
AN426AD3-4.5 to 3.5 37 psi 1 ½ seconds
AN426AD3-6 plus 40 psi 1 ½ seconds
AN426AD4-4 to 4-5 45 psi 1 second
AN426AD4-6 to 4-9 50 psi 1 ½ to 2 seconds

AN470 Rivets:

Rivet Type Air Pressure Duration
AN470AD4-4 to 4-5 60 psi 1 second
AN470AD4-6 to 4-7 60 psi 1 ½ seconds
AN470AD4-8 to 4-9 75 psi 1 ½ seconds
AN470AD4-9 plus 80 psi 1 ½ to 2 seconds

The critical part of riveting is to let the bucking bar do the work by RELAXING your hand pressure on the thing to allow it to come off the rivet when the gun strikes it and then bounce back to act as a hammer. It doesn't take much. It's a real "feel" thing. Eventually it'll feel like you're forming the shop head with the palm of your hand. So it's important to be able to control the bucking bar. You can't do that well if the psi on the gun is blasting the **** out of it.

The best example I've seen of what's happening here is those little desk desk displays of the four bearing suspended by springs. You pull one on the end back and let it go, and it hits all three balls, but only the one on the farthest end responds, then swings back and hits the three, and the original one on the end is the only one that responds etc.

Keep good solid pressure on the gun so that when the bucking bar (in this case the far bearing) comes back and strikes the shop head, it doesn't, in turn, push the rivet gun off the manufactured head, which is how you get smileys and -- when doing flush heads -- raised rivets.

Be one with your bucking bar.
 
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I recently bought a big heavy bucking bar, I think it is about 3 lbs , I do not remember for sure but for -4 rivets I love it. I hit the rivet very slowly and it is very controllable.
 
I've had good luck keeping the shop air set at 90psi, and using the brass click-type adjustable regulator on the rivet gun to set the pressure. To achieve repeatable results, I made a mark on the adjustable regulator that I use at my reference. Then I record the number of turns & clicks past my reference mark for each type of rivet.

Actually, there are only two entries in my rivet table. One is for the typical skin rivet (like an AN426AD3-3.5) and the other is for a typical structural rivet (like an AN470AD4-5). Having those two starting points seems to be close enough, and you can always make adjustments as you go.

Good luck!
 
IowaRV9Dreamer said:
I've had good luck keeping the shop air set at 90psi, and using the brass click-type adjustable regulator on the rivet gun to set the pressure. To achieve repeatable results, I made a mark on the adjustable regulator that I use at my reference. Then I record the number of turns & clicks past my reference mark for each type of rivet.

Actually, there are only two entries in my rivet table. One is for the typical skin rivet (like an AN426AD3-3.5) and the other is for a typical structural rivet (like an AN470AD4-5). Having those two starting points seems to be close enough, and you can always make adjustments as you go.

Good luck!
Click to expand...

I'll have to agree here. I find that using the click type "regulator" allows me the to make adjustments quickly. I tend to count blows too if I can. I try to set a rivet in 3-5 blows and some longer rivets require more like 6-8.

I'm on the fuselage and I'm still learning a little bit-- the 3's are easy to overdrive.

On a different note. For me, poor quality of the hole and alignment of holes the parts being riveted are almost always indicators of a rivet that is going to be harder to drive. For example-- A hole that is say 15% elongated will tend to want to produce a clenched rivet. Similarly, I can recall having shot a few rivets that the hole wasn't drilled perfectly and the rivet wasn't 90 degrees to the sheet ant they required more finess to shoot
 
they are not all 4-7, check your plans carefully, only the inboard ones are 4-7 which go through all three spar materials, on the outboard side (last four ribs) it is actually a 4-4 I think
 
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