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Riveting short stringers on RV-10 Horizontal Stab

missile29

Member
Hi,

Any thoughts / tips / advice on best way to buck the rivets attaching the HS-1015 short stringers to the skins on an RV-10 horizontal stab? There are 20 of these rivets total, 10 per side, 5 top, 5 bottom, and the tricky thing about these is the fact that you can't really see the back (shop head) side of these rivets, because you're reaching in from the back (from where the read spar would be) and need to reach around to the front (leading edge side) of the stringer to hold the bucking bar.

I've been assuming I would go by feel, and then use a mirror to peek up in there to verify they are set properly. I'll also use the little gauge I have to check then shop head dimensions. But I'm wondering if folks have any advice on a specific bucking bar that works well to reach up and behind the stringer, or any other tips and tricks, because I'm sure this won't be the last time I have to buck a rivet that I can't reach or see properly.

Thanks!
--mgm
 
I don’t have the plans right in front of me for that particular part, but here are three tips I use for small spaces that are hard to see:

(1). Use a smaller bucking bar made of tungsten. Pricey but worth their weight in …tungsten.

(2). I sometimes wrap the sharp corners of the bucking bar (that may make contact with an edge inside the structure) with a couple of pieces of masking tape just to soften the edges a bit on the bar. Use two people if you can (one to buck and one to rivet) so you can get in the best position to hold the bucking bar. I try to avoid riveting yoga if I can and my wife is a great riveter.

(3). An old timer taught me a trick for when you can’t see the shop head in a tight space. Firmly press your finger on the shop head when you’re done and you should have an imprint on your finger for a few seconds that shows you how wide the shop head is. If the width is the same as the other good rivets you’ve done it’s probably good enough.
 
Thanks, I like the finger imprint trick. Clever! I'll definitely be using a smallish tungsten bar, with taped edges. I'll probably put some padding at the bottom of the hole because I'm deathly afraid I'll drop the bar and dent something in there.
 
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Things I do in those cases:
- I use a cheap endoscope camera to see the other side.
- I cut a slice off a porous sprinkler drip line and tape it onto the bucking bar where I want the shop head to sit. I can then easily test whether I have "captured" the rivet on the other side by feeling the freedom the bucking bar still has concerning side movements. You test that again between spurts.
- I get a second person. So much easier if your role is just to get the bucking right and not have to rivet with the other hand.

One more thing: the basic principle of riveting with the gun is that you have to push the rivet backwards (and therefore the object you are riveting) and slam it into the bucking bar. Goes so fast, you don't see it. That is easy with skins and ribs because they flex. As the "objects" become sturdier and heavier, like a spar or a longeron, make sure the object can move freely, e.g. by putting it on foam. And cushion any stop that keeps it from moving.
 
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Things I do in those cases:
- I cut a slice off a porous sprinkler drip line and tape it onto the bucking bar where I want the shop head to sit. I can then easily test whether I have "captured" the rivet on the other side by feeling the freedom the bucking bar still has concerning side movements. You test that again between spurts.

Very intrigued and trying hard to picture this... I think I know the basic idea, because I've done a similar thing just with tape on the bucking bar and moving side to side until I can feel the tape hit the rivet shank. But I'm not sure I understand the sprinkler drip line.
 
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