Rivet heads breaking off.

azav8or · #1 01-27-2006, 09:09 AM

Has anyone had the machined head of the rivet break off while setting a rivet? I am working on attaching my ribs to the main spar and I have had 3 break off. It has looked like it sheared level with the flange of the rib. I am using the double offset. The broken head shows no smilies.

This is the second spar and I had no problems with the first spar but now wonder if there is a problem I should be concerned with. I compared the double offset rivet set to a straight set and it appears the double offset is a little flatter at the bottom of the cup than the straight set. I switched to the straight set and the rivet heads appear to be better.

My main concern is whether or not the ones that didn't break off are structurally sound. They appear a little more flattened (very slightly) but I am cautious about things like this. The thought of drilling out every rivet in the main spar scares me. Any thoughts would be greatly appreciated.
Thanks, Joe

vlittle · #2 01-27-2006, 09:13 AM

Your double-offset set may not be right. If you bought it retail from a reputable supplier, it should be ok.

If it's Boeing surplus it might not be right. It's hard to tell. There are a lot of specialty rivets out there.

I'd also make sure you don't have a bad batch of rivets, and that you've deburred the rib holes properly.

Very strange.

alpinelakespilot2000 · #3 01-27-2006, 11:38 AM

Make sure you are not trying to strike the rivet too long after you do the first shot. The rivets work harden and are more likely to crack the heads. If this is not the reason, I'd think it must be a bad rivet set or the set is bounciing on the factory head.

Snap Socs from Avery will work well at protecting the head of the rivets. I used them on my spars and had no drill outs, and not because I'm a great riveter!

HOpe this helps a little. Good luck.

azav8or · #4 01-27-2006, 03:10 PM

Thanks for the replies. I have the books that came with the Avery kit that say to set a rivet in 2 1/2 to 3 seconds. I bought Dan's cd that says he takes average 1 1/2 seconds. Am I hitting them too long? Am I work hardening them?

Thanks again. I greatly appreciate it. Joe.

sf3543 · #5 01-27-2006, 03:29 PM

If you are getting the correct size shop head, after a 1 to 2 second burst, or up to 3, 1 second bursts, you should not be work hardening them.
If you have the rivet gun set too low (air pressure) and you are requiring long bursts or longer multiple bursts, then you are. You should either increase air pressure or go to a larger rivet gun.
For the spars, you should have at least a 4X rivet gun or larger, or set them using a heavy hammer in a C frame or arbor press. When I did my -6, I used a 2 lb sledge in the reinforced Avery C Frame. It worked great with no need to drill out any rivets. If you use care in setting everything up, the manual "armstrong" method works well.
Good luck.

cjensen · #6 01-27-2006, 03:30 PM

i think 2.5-3 seconds is too long, especially if your gun is set lower than it should be? 1.5 seconds has worked great for me, but the pressure needs to be adjusted for the size of rivet. if you can count the hits, at the correct pressure you should get about 5-6 at the most.

what size gun do you have, and what pressure are you using? sounds work hardened to me. also, maybe you are pushing to hard with the bucking bar that the head is pushing out and allowed to "wobble" a little?

azav8or · #7 01-27-2006, 03:45 PM

I am using a 3X gun. I have an Avery pressure adjuster at the gun. I used enough pressure to set the shophead properly in 2 1/2 to 3 seconds assuming that must be the right. I am going to remove the adjuster at the gun and use Dan's recommendations unless there is a reason why I shouldn't. I appreciate all of the inputs. The offset I bought was from Avery and they are sending out another for me to compare with my existing. Great folks at Avery.

Thanks all, Joe.

alpinelakespilot2000 · #8 01-27-2006, 05:27 PM

It doesn't matter whether it takes 1.5 second or 5 seconds to set the rivet. Just don't stop striking it and then come back later (after 15-20 seconds) and strike it some more. Find a duration for striking and corresponding pressure setting that works is controllable and consistent for you and stick with it. Just my opinion...

szicree · #9 01-27-2006, 05:43 PM

I'm certainly no metalurgist, but after setting what seems like a billion or so rivets on my now completed airframe, I have had not one single rivet head snap off. I'm sure that I have gone more than 3.5 seconds and less than 1 on a number of occasions. The fact that you've already had several heads come off suggests that something is way off. I'd take a good look at the rivet set. For example, suppose the set had sort of a pimple in the middle. This could focus the hit right through the center, rather than distribute it. Check the rivets themselves. Maybe they're flawed. I had a couple of AN screws with no threads whatsoever. I know this is quite obvious compared to a defective rivet, but there could be a problem. I guess I'm just saying that if rivetting for an extra second or two causes rivets to fly apart, we should all have timing controls on our guns. I think your trouble is equipment/material rather than timing. Just my dopey opinion, of course.

rv9aviator · #10 01-27-2006, 06:03 PM

I'm not sure I wouldn't try a different batch of rivets from a different supplier or bought at a different time to see if you might have some bad rivets. I have built my empennage and both wings and have yet to have the manufactured head shear off a rivet. I never set a rivet before I started my empennage.