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control surface practice kit question - deforming rib flange

R

ryane67

Active Member
I had a friend over today and we were building a control surface practice kit, wow they really go fast with 2 people and you form an assembly line type situation..

Anyway, when we were riveting the rib to the spar and the doubler, we came across something I could not explain.

We used AN470AD4 as described in the plans, with the manufactured head on the doubler side. When using the pneumatic squeezer to create the shop heads, the rivet squished nicely but it practically dimpled the rib flange!
The 3-layers of metal directly surrounding the rivet were tight but further away from the rivet a gap between the spar and the rib flange becomes apparent. EDIT: to be clear, there was no rivet squeeze-out between the 3 layers of aluminum.

Drilled out the rivet, cleaned up the flange, repeated the process, but it happened again! really scratching my head here, but moved on to the other side knowing this is not something we'd be OK with keeping on an actual plane.

On the other side I decided we should reverse the rivet (manuf head on the inside, thinner material) and use an offset set with the gun and bar.. those two came out nicely and no deforming metal.

Is there something about using the squeezer on 3-layers? Is it something to do with pressure applied to thinner vs thicket materials stacked together? Trying to learn from this because I know there are places where you've got 3 layers to rivet together pretty early on in the empenage and I'd rather trash scrap than the real thing :)
 
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Has anyone else encountered this or have the answer? My searches through the forums have failed me.

I'm running my squeezer at recommended pressure, but I'm thinking the pressure needs lowered with the thin rib on the shop head side. I've already drilled out and tried again. Bucking bar and rivet gun led to less deformation but still noticeable.

Thanks,

John.
 
You’re probably squeezing at a slight angle. That’s my guess. And try a hand squeezer where you can control the pressure better.
 
Better than average chance it's not 100% straight. I've attached a couple of pictures of one rivet (same rivet both pictures) to give a better idea.

I'll try better pressure control and see if that changes it.

Any additional feedback on this? Thank you.
 

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I defer to vans recommendation to put the manufactured head on the thinnest material and the shop head on the thickest. Does not matter how it looks on the outside on the spar as it’s not really seen. At times you cannot do that and a certain amount of puckering is inevitable and ok. On my wing and tail spars I placed the shop head on the outside as this is the thickest material. Not really a problem on spars as they are thicker but ribs are thin…and they can lift. Like this on my fin….shop heads out. not required and many do it the other way to keep the rear surface “clean” for painting. But to me just looks normal for the structure.
 

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I would think that because you are pulling a little on the manufactured head with your squeezer (and thereby making sure the layer touch) it makes sense that you get better results because the thinner layers will be pulled towards the thicker more easily. With two layers it’s pretty easy to make one good contact, but with three you can get small air gaps between layers, which get amplified and frozen when you squeeze the rivet, even when it’s relatively straight and doesn’t really show any squeeze-out. Doesn’t take much.

Have you tried manually holding the three layers together with a clamp before riveting? That should get better results no matter which side you put the manufactured head. You can use your fingers to hold the layers together if you can make sure not to squeeze them with your squeezer.
 
Looking at your pictures this makes even more sense to me. The two layers adjacent to the manufactured head are in good contact, but there is that gap to the third layer. I’d just clamp it with a cleco clamp nearby and it should work.
 
Here's a great trick to put in your toolbox... cut a small section of tubing (I used model airplane silicone fuel tubing). Make the length of the tube about as long as the rivet shank. Insert the rivet in the parts and slide the tube over the shank of the rivet that sticks out. Then partially squeeze the rivet. The squeezer will impact the tubing first and clamp the parts together before it begins forming the shop head. Experiment a bit with the length of the tube.
 
georgemohr said:
Here's a great trick to put in your toolbox... cut a small section of tubing (I used model airplane silicone fuel tubing). Make the length of the tube about as long as the rivet shank. Insert the rivet in the parts and slide the tube over the shank of the rivet that sticks out. Then partially squeeze the rivet. The squeezer will impact the tubing first and clamp the parts together before it begins forming the shop head. Experiment a bit with the length of the tube.
Click to expand...
I use a similar trick, a rubber washer. Same principle, holding the pieces together, then form the shop head.
 
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