This week: cracked elevator rib dimples

RV10Rob · #1 12-16-2007, 01:27 PM

Hi, all... last weekend was cracked rivets; this weekend, it's cracked elevator rib dimples. I'm back riveting the ribs to the skins and getting several cracks in the dimples. Here's a particularly bad one (most of them are barely visible):

Notice I'm a little off-center on the riveting, but it doesn't seem that bad. Also, I think my deburring is good. Any ideas? It's not too cold this time

-Rob

Captain Sacto · #2 12-16-2007, 09:49 PM

Rob, your picture looks quite familiar.

I put a crack into a dimple in the top half of the front HS flange, and I still haven't decided what to do. I did get some good suggestions (see http://tinyurl.com/yrglnl ) and I'm thinking that I'll probably stop-drill and put in a universal rivet on each side, for additional strength (luckily, I have no plans of making a show a/c).

Please post any advice you get (e.g. from Van's), and good luck with the "fix".

Regards all - - Tom

paul330 · #3 12-17-2007, 05:05 AM

I did my elevator ribs not so long ago in chilly UK and had no problems. Looks from the photo like you have an oversize hole and have "caught" the edge as the rivet expanded. Are you perhaps being a little over-zealous with the deburring? The skins are very thin and just a half twist with the c/s tool is all that is required.

Jamie · #4 12-17-2007, 05:48 AM

Not sure what the cause of that crack is, but you could probably just drill out the hole to #30 and put an oops rivet in there.

cytoxin · #5 12-17-2007, 06:16 AM

i dont think a 30 will clean that up. your only talkin .031 which equates to .0155 per side.
are you drilling the holes or reaming...some like to ream but this technology is designed for drilling....with a 30 or 40 drill bit.
not a 31 or 41
is that already an oops rivet? if so next time when using an oops on a thin skin dont set it all the way. or it can stretch and crack. not always but occasionally. YMMV good luck

az_gila · #6 12-17-2007, 07:31 AM

Rob... post a picture of one of your typical holes after deburring....

Also, how many "hits" did you have with your 3x (my guess...

...) rivet gun to set the rivet?

Could you be hitting the rivet with too few "big" hits?

gil A

JonJay · #7 12-17-2007, 08:37 AM

Although difficult to tell from the pic, it looks like your rivet was too short. A short rivet can swell in the hole instead of forming a nice shop head, especially if you hit it too lightly, too many times, and work hardened the rivet.
Your dimple also may not have been formed all of the way, and/or, your two pieces seated together well before you riveted allowing the rivet to swell between the pieces, making the rivet look too short.
Same result, too much swelling of the rivet in the hole, and the shop head does not develop properly.

RV10Rob · #8 12-17-2007, 01:40 PM

Thank you all for the replies. It does seem like the holes are a little big. I don't think I was too aggressive with the match drilling and deburring, but I might be wrong. Here's something I don't understand: for the 3/32 rivets, if you match drill with a #40, the rivet fits. If you then deburr slightly and dimple, don't both of those operations enlarge the holes? Would it make more sense to match drill with a smaller bit?

To answer the other questions...
- The picture is not of an "oops" rivet; just a standard AN426AD3-3.
- The rivets weren't too short before driving (pretty much exactly 1.5x width from top to the top of the dimple).
- I'm using a 2x gun... hard to remember the setting... maybe 30# and 1-1.5 seconds each?
- I don't have a picture of a deburred, dimpled hole, but I can take one when I get home

For the one, I'll just replace the rib. Most of the other cracks are tiny, so I figure I can drill out and use an "oops" rivet for those (unless there are too many for one rib).

I don't doubt my ability to fix the problem; I'm more concerned about figuring out what I'm doing wrong in the first place.

Thanks again, all...

-Rob

cytoxin · #9 12-17-2007, 04:54 PM

Quote:

Originally Posted by RV10Rob

Thank you all for the replies. It does seem like the holes are a little big. I don't think I was too aggressive with the match drilling and deburring, but I might be wrong. Here's something I don't understand: for the 3/32 rivets, if you match drill with a #40, the rivet fits. If you then deburr slightly and dimple, don't both of those operations enlarge the holes? Would it make more sense to match drill with a smaller bit?

To answer the other questions...
- The picture is not of an "oops" rivet; just a standard AN426AD3-3.
- The rivets weren't too short before driving (pretty much exactly 1.5x width from top to the top of the dimple).
- I'm using a 2x gun... hard to remember the setting... maybe 30# and 1-1.5 seconds each?
- I don't have a picture of a deburred, dimpled hole, but I can take one when I get home

For the one, I'll just replace the rib. Most of the other cracks are tiny, so I figure I can drill out and use an "oops" rivet for those (unless there are too many for one rib).

I don't doubt my ability to fix the problem; I'm more concerned about figuring out what I'm doing wrong in the first place.

Thanks again, all...

-Rob

but this technology is designed to work just as all the books show. you should only debur 1 to 2 turns max with light to no pressure the idea is to simply remove the burs not counter sink the hole. if you enlarging the hole you are overdoing it.

tim.randles · #10 12-18-2007, 08:08 PM

Is this a problem you're more likely to see on driven than squeezed rivets? Is it something that would be rare on the thicker skins (.032 and thicker)? It would seem so to me, but I'm just getting started. Seeing this issue crop up makes me a little nervous now because I didn't closely inspect all of my driven rivets all the way around their circumference when putting my vertical stabilizer together.