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  #1  
Old 08-14-2021, 12:04 AM
ScottK ScottK is offline
 
Join Date: Feb 2007
Location: SLC, UT
Posts: 56
Default Riveting elevator upper skin to spar

I know this is an often visited subject, but I promise if I'd found the answer by searching previous threads I wouldn't be posting again.

The short version: If I proceed to run the upper-skin-to-spar rivets using a back-rivet set and plate, what unseen problems am I apt to find?

Long edition: I have progressed to the point of attaching my elevator skin to the spar. From my previous query I've figured out how to work inside the skins (in my case, wooden angle braces and a lot of spring clamps). But as I feared, the spar riveting is a puzzle: since I have limited function in one hand, I'm not able to hold a bucking bar in the needed position under the spar while I run the gun with my good hand. On other pieces I got by with the help of gravity and a variety of wood cribbing, but I don't see that working here. One answer would be to get a rivet buddy from my local EAA chapter, but with Covid still in progress I'd rather not just yet.

So: I've been able to get some of the rivets in with a squeezer - a few on each end, and a few around each hinge hole. About a third of the total, enough to hold it together. Now I'm thinking to flip it over, stick a steel plate under it, and apply back-riveting. A careful look at the spar flange shows that it's bent a bit less than square, about 83 as I see it, which looks like enough to get the set square on the rivet. My set is a bit longer than some, so the nose of the gun is clear of the work.

It seems plausible. What am I not anticipating?
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  #2  
Old 08-14-2021, 10:54 AM
Jslow2 Jslow2 is offline
 
Join Date: Dec 2020
Location: Cement City
Posts: 142
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I don't see how you could get the back rivet set straight on the rivet inside the spar.

I clamped they lower skin to the table, held the upper skin open with an empty box wedged between the upper skin and the wall, holding it open around 90 degrees, the upper skin sitting vertical. I stood with the upper skin in my armpit, with that arm inside the elevator reaching around the spar with my small tungsten bucking bar, and bucked the rivets from the outside with my other hand. Was a learning experience, put some dings in the top skin that I will decide what to do with over the next two or more years
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  #3  
Old 08-14-2021, 10:06 PM
ScottK ScottK is offline
 
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Location: SLC, UT
Posts: 56
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Quote:
Originally Posted by Jslow2 View Post
I don't see how you could get the back rivet set straight on the rivet inside the spar.
Apparently without too much trouble - see attached pic. Much like you describe, I have the top skin clamped to the table, and a 2x4 brace holding it open. I posed my rivet gun pretty much where it can go, it's on a rivet tail and bumped up against the upper flange (I'll need to do something to avoid dinging the flange). I posed a combo square next to it, you can see that the gun is only a couple degrees off square, but close. I still want to think about it before I pull the trigger, but I'm optimistic.

Quote:
I stood with the upper skin in my armpit, with that arm inside the elevator reaching around the spar with my small tungsten bucking bar, and bucked the rivets from the outside with my other hand.
Yep, that seems like the usual approach. It's sensible. But when I said "limited function in one hand", I mean...limited function.
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  #4  
Old 08-15-2021, 04:31 AM
Jslow2 Jslow2 is offline
 
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Guess I should have tried that lol. It's throw some tape on the lower skin flange and try one, if anything you could probably grind a little off the shaft to get the extra few degrees.
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  #5  
Old 08-15-2021, 10:59 AM
nohoflyer nohoflyer is offline
 
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  #6  
Old 08-16-2021, 07:00 PM
ScottK ScottK is offline
 
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I'm pleased to report some success, it isn't perfection, but I was able to back-rivet this line after all. It takes more attention, pulling the skin open causes the surface to curve back on itself creating a gap between skin and plate, without a good deal of pressure from inside and a carefully placed plate, it's a recipe for setting rivets with heads sitting proud of the surface. But this one turned out OK, and the next one will be better.

Quote:
Originally Posted by nohoflyer View Post
Thank you! That's the info I didn't know I needed. A bit too late for this set of elevators, as I've already prepped them for CS4s on the bottom (guess I could use 426-4s instead...or just stick to the plans...). But good info for the next challenge in any case. That EAA video alone is worth the price of admission.
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  #7  
Old 08-17-2021, 04:45 PM
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tyconnell tyconnell is offline
 
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In the category of "over engineered for this application, but very cool", this EAA video shows a custom bucking bar that they used to rivet a 14' Ford Tri-motor aileron spar.

Need an EAA membership to view.
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