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Dimpled wrong size in elevator skin bottom

sbal0906

Well Known Member
I sent this question to Vans support but I thought I'd ask here too. I accidentally went ahead and drilled and dimpled all of the bottom holes of the elevator skin that are for riveting to the spar to #40 instead of some to #30 to accommodate the CS4-4 pop rivet.

Is it ok to enlarge a dimpled hole to #30 and re-dimple to 1/8"?
 
The problem is that this is very hard metal and you only have 1 or 2 shots at deforming it before it cracks. You could try on some scrap and see what kind of job it does. I can't say for sure but I wonder if there is a risk of cracking. Please post what VANs position is.
 
You should be just fine. 2024 T3 is not very forgiving as Scott eludes to, but I would have no concerns over drilling these to the next size and dimpling with the #30.
 
I've done that

I have a few places on the M2 where a test rivet is needed to hold a structure - before the final #30 size is put in. Once you over drill for the #30 dimple the potential crack area is minimized if not completely eliminated. Granted I've not done as many as you will now do, but as long as your spacing is correct for the #30 holes, each hole is essentially a loner and should pose no problem.

If you wanna get some feel good before you proceed, and see just how resilient 2024 is/is not, take a scrap and put a dimple in it. Then reverse the dimple and see how many times you can do that before you induce a crack. Its probably three. And youre not even close to doing that to the metal youve got.....
 
Try this on a scrap: drill #40 and dimple 3/32. Then drill it out to #30. But, don't re-dimple. Set the CS-4-4 rivet and see if it doesn't set flush. I think it might work just fine.
 
Thanks everybody for your input! I haven't heard from Van's yet but I'm feeling more confident about it. And yes, I'll try it out on some scrap and compare just drilling a dimpled #40 hole to #30 to drilling and re-dimpling the hole.

Cheers, :)
 
So I did two tests - one just drilling to #30 and not increasing the dimple and one drilling and dimpling

With just drilling but leaving the dimple as is, the CS4-4 rivet head sits just slightly high. Just enough to catch a fingernail. With the other test, after dimpling to the larger size, I suddenly felt silly even asking this question because it's not like I'm working the metal back and forth. I'm just deforming the metal just a little bit more in the same direction it was going in the first place. So that turned out fine.

Van's support recommended using MK-319-BS rivets which would require drilling to 7/64" (or #34) and would work in the same dimple. I tested one and it would look better from an aesthetic point of view since that row of rivets will have a mix of pop rivets and AN426AD3 rivets. I would have to buy more MK-319-BS rivets so I thought if I'm doing that, why not just get 3/32" pop rivets like the Cherry "N" CCC-32 rivets? That way, I wouldn't have to re-drill the holes.

Cheers,
 
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Because Wicks Aircraft lists the shear strength of that rivet at 230 lbs.

AN426AD3 rivets are rated at 275 lbs

Ah.. good point. The question here though is how CCC-32 compares to the MK-319-BS which is recommended by Van's support. Some googling brought that discussion back to this site. Go figure.

Strength of the MK-319-BS according to (http://www.hansonrivet.com/blind-rivets-monel-steel.htm is 258 lbs shear and 280 lbs tensile. I'll stick with these.

Thanks,
 
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