clinched rivets advice needed

sglynn · #1 02-15-2009, 12:34 AM

How strong are clinched rivets? Do they always need to be drilled out and replaced? Can I reshape the shop heads to fix a clinched rivet? Your comments are appreciated. I'm building a 7a and the row of rivets along the main wing spar that hold on the main skin came out clinched. I back rivetted them originally and they looked fine. But when I turned the wing up side down and put it into the cradle I saw that most of the rivets clinched or tilted. I'm now trying to flatten the shop heads a bit more to cover up the entire hole using the rivet gun and bucking bar. This kind of works. I'm worried about drilling them out because the holes will get slightly large. But if the clinched rivets are too weak then I guess I'll drill 'em. Is there any negative aspects to shop heads that are a little larger then spec? Did anyone else see this and end up with clinched rivets along this row of rivets? What did you do about them. Your comments about clinched rivets and when they should be drilled out are appreciated.

sprucemoose · #2 02-15-2009, 01:05 AM

Steve,

Do you have a picture? That would be helpful. Also, you mention rivets being slightly over-driven after fixing them. Do you have a dial caliper, and if so, can you take some measurements of the rivets in questions (height and diameter) so we can make a more informed analysis.

My gut instinct is to say that you are probably OK but I'd like to see the pics and numbers to be sure.

sglynn · #3 02-15-2009, 10:09 AM

Here are photos of the clinched rivet problem. Your comments are appreciated.

http://www.mykitlog.com/users/worklo...photo_number=1

http://www.mykitlog.com/users/worklo...photo_number=2

http://www.mykitlog.com/users/worklo...photo_number=3

You can also see on my log at http://www.mykitlog.com/users/displa...og=71917&row=1.

Danny7 · #4 02-15-2009, 10:15 AM

Hi Steve- glad to see you are getting stuff done, I'm still on the empennage. I must need to put the nose to the grindstone for a couple of good days and finish my tail off.

regarding your clinched rivets, you know i have way less experience than most here, but i'd re do all the rivets in your third picture, the one with the nut plate. the shop heads don't cover half of the material to be riveted together, I think anytime you can see 40% or more of the drilled hole you are looking at a singnificantly weaker fastener. just my inexperienced opinion.

in your preview plans, page 5-23, on the first row of seven examples, look at the fifth one in. That looks similar to yours, not exactly, but they say to replace it.

sprucemoose · #5 02-15-2009, 10:41 AM

Are the clinched rivets in the photos the only ones, or is the entire row on the spar like these? If it's just these, I would probably leave them. Not every rivet is going to be perfect, and the occasional bad one is not going to bring down the plane. However, if the entire row or much of it is like this, then I would replace them. You should get yourself lots of practive at drilling out rivets on scrap, and have an experienced builder demo the technique.

If you do oversize the hole a bit that's not the end of the world, as you can usually just drill it out for the next bigger size rivet and use that.

As a side note- be careful about using the little rivet gauges as a go/ no-go gauge. Familiarize yourself with the Mil-spec on riveting, and the requirements for shop head dimensions. There is a fair amount of wiggle room between the Mil-spec requirements, and the size of the rivet gauges or the 1.5X rule of thumb. Within this wiggle room are a lot of perfectly acceptable rivets that have been drilled out unnecessarily because they failed the rivet gauge.

Drilling out a rivet is not neccesarily bad, but it is risky, and if done badly often makes the problem worse than what you started with. Practice, practice, practice on scrap.

http://www.vansaircraft.com/public/Specs.htm

sglynn · #6 02-15-2009, 03:32 PM

Okay, I drilled out all the clinched rivets and re-rivetted them using the forward rivet process. Bucking bars work. Now they are perfect. Only took 2 hours per wing. Almost faster to drill out and redo then to post on Vans Forum. One thing is I used a #42 drill bit which is sufficiently wide to still snap off the rivet mfg head, and tap out the shank. And it guards against making the hole bigger. I drilled out 120 rivets per wing. But no big deal. Once you get on a roll and keep the drill bit centered, the rivets can be drilled out without issue. So, now the wing is as it should be and I feel better. Under the new rivets you can see where the clinch foot use to be. PS, I did pre squeeze a few rivets to fatten their shanks, but this wasn't really necessary.

http://www.mykitlog.com/users/worklo...photo_number=1

http://www.mykitlog.com/users/worklo...photo_number=2

Rick6a · #7 02-15-2009, 04:07 PM

Quote:

Originally Posted by sglynn

Okay, I drilled out all the clinched rivets and re-rivetted them using the forward rivet process. Bucking bars work. Now they are perfect. Only took 2 hours per wing. Almost faster to drill out and redo then to post on Vans Forum.

Well done Steve! Too many people leave bad rivets in place believing they will do more damage and that is unfortunate. Anybody who shoots rivets into an aluminum airplane should develop the skill necessary to drill out bad rivets. It comes with the territory. The skill is downright essential in the production world where even long time pros mess it up from time to time. I'll wager the Piper Dakota you fly has precious few defective rivets pounded into its airframe and neither should your RV.

Geico266 · #8 02-15-2009, 04:36 PM

Good call Steve, and great technique drilling them out. I was going to advise you to replace them. While a few bad rivets are not going to bring the plane down, the ones you can see that are bad need replacing. Those were bad.

Danny7 · #9 02-15-2009, 05:17 PM

Quote:

Originally Posted by sglynn

Okay, I drilled out all the clinched rivets and re-rivetted them using the forward rivet process. Bucking bars work. Now they are perfect. Only took 2 hours per wing. Almost faster to drill out and redo then to post on Vans Forum. One thing is I used a #42 drill bit which is sufficiently wide to still snap off the rivet mfg head, and tap out the shank. And it guards against making the hole bigger. I drilled out 120 rivets per wing. But no big deal. Once you get on a roll and keep the drill bit centered, the rivets can be drilled out without issue. So, now the wing is as it should be and I feel better. Under the new rivets you can see where the clinch foot use to be. PS, I did pre squeeze a few rivets to fatten their shanks, but this wasn't really necessary.

http://www.mykitlog.com/users/worklo...photo_number=1

http://www.mykitlog.com/users/worklo...photo_number=2

between this and your HS i think if i need any professional rivet removing i'll call you.

glad you got them fixed.

jsharkey · #10 02-15-2009, 05:34 PM

Clinched or cleated rivets usually mean that there wasn't a direct compression load on the rivet to swell it in the hole. If that's the case they tend to pop out easily once you drill the head off. Ironically if they are a bear to punch out after drilled they were plenty strong to start with. Ugly is then a good reason to change them

Jim Sharkey