Curling flanges. Did it happen to you?

I'm at the point to finalized riveting the wing ribs to the aft spar. The problem I have is when the rivet is almost set then the flange ends up "curled" some how (see image attached). It does that only on the top or bottom rivet hole.



Did that happened to you? If the rivets were inserted the othe way around, perhaps that wouldn't happen. But I've already set most of the rivets (AN470) with the manufactured head on the outside face of the aft spar.

I've seen that trick on Kitplane mag (Eliminate Gaps While Riveting - March 2014). I guess this is the way to go.

I have installed about ten of them out of 50. Should I remove them or there is nothing to be concerned with? The flange itself seem to sit on the spar but it doesn't look good. Or it is simple just not acceptable?

Better results if you put the manufactured rivet head on the thinner material side.

AC 43 has specifics on acceptable gaps under rivets using a feeler gauge.
With experience, and if you are careful, you can place a bucking bar next to the shop head and tease it flat with your rivet gun.

I had this happen riveting nose ribs in the horizontal stabilizer. Some of the flanges are so small they only contain a single rivet hole, and you're instructed not to dimple them. It improved significantly driving the rivets with the manufactured head against the flange but it didn't go away entirely. I even tried to carefully set the rivet with short bursts before finishing them and the curling didn't appear until the final few strikes when the shop head reached the minimum diameter. I can't get the thinnest feeler gauge near the rivet, but the appearance certainly does not inspire confidence.

Okay. I've tried a technique that returned very acceptable results. I did use a "plumbing" washer but the one I used is slightly different. It has a zinc plated washer glued on the rubber washer and the hole size was a tad smaller. I used it to set the rivet partly then I finished it using a AN960-10 washer taped on the bucking bar.

With this I manage to "bend back" the ribs flanges to an acceptable gap as per AC 43 specifications. I've tried a .001 gap filler and it wouldn't slip near the rivet.

(before and after)

(zinc plated/rubber washers)

(AN960 washer taped on bucking bar)

(setting a rivet with the bucking bar)