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Empennage Skin Bumps After Riveting

Hello all,

I'm a long-time lurker, but this is my first posting (so go easy on me). I've done a search on this but didn't find anything quite like this, so apologies if it's been covered...

I just finished riveting the skin, other than the rear row of rivets, on my HS, and overall I thought things were going pretty well for me...but after finishing, I noticed than in a few spots, I had a "pimple" (one of which, pictured below, was fairly large). I've finished the vertical stab without these issues, so I'm not sure where I went wrong here:

IMG_1907.jpg


IMG_1909.jpg


My questions are:

1. How did I FUBAR this? My only guess is that I didn't do a good enough job of rounding off the faceting in the flange of the ribs during prep in a few spots, and it caused the skin to deform as I riveted it together, but I want to make sure that's where to focus my energy.

2. Other than aesthetics, is there a problem with building on with a few spots like this in the skin?

3. Is there anything I can do to improve the damage I've done? I'd thought about trying to push the dent inward with a light attack from a flush set, but I don't want to make it any worse than it already is, or cause an ugly part to become an unserviceable one.

I'm planning to arrange a Tech Counselor visit when the weather in New England and my schedule align to do so, but in the meanwhile I figured I'd get the Internet's collective wisdom. Any help you can provide would be appreciated!
 
Looks like something was under the skin (metal shaving?) when you bucked the rivets. If accessible, you might be able to use a thin piece of metal to fish it out and smooth the skin a bit but a mark will remain. It can be fixed during paint prep.

Build on.
 
Could be the edge of your bucking bar. Make sure that before you set the rivet that the bucking bar is parallel to the rivet joint. You will develop a ?feel? when bucking a rivet out of sight by extending your fingers past the edge of the bucking bar to feel that the edges of the bar are equidistant to the surface of the skin you are riveting. All part of the learning process.
 
Could be the edge of your bucking bar. Make sure that before you set the rivet that the bucking bar is parallel to the rivet joint. You will develop a ?feel? when bucking a rivet out of sight by extending your fingers past the edge of the bucking bar to feel that the edges of the bar are equidistant to the surface of the skin you are riveting. All part of the learning process.

Regarding the dent: Agreed. The edge/corner of the bucking bar pushed the skin out. Wally Anderson from Synergy Air told me, during my build class, if that happens I should "turn the 'outie' into an 'innie' and then fill it before paint.

Have you checked to make sure your rivet set and/or dimple dies are perfectly smooth? I don't know how to account for the scratches right around the rivets, but that would be my guess.
 
Could be the edge of your bucking bar. Make sure that before you set the rivet that the bucking bar is parallel to the rivet joint.

Understood. Since it hadn't happened to me up until this point, I thought I was getting a feel for it, but apparently am still bracketing. All the bumps occurred when I was holding the bar at a particular angle (for access), so it must have been more "off" than I thought.
 
Wally Anderson from Synergy Air told me, during my build class, if that happens I should "turn the 'outie' into an 'innie' and then fill it before paint.

How exactly would you suggest I do that? Like I said, my gut feeling was to hit it with the flush set lightly until it went down/the other way, but I want to make sure I'm not missing anything.

Have you checked to make sure your rivet set and/or dimple dies are perfectly smooth? I don't know how to account for the scratches right around the rivets, but that would be my guess.

I see what you're referring to, but I'm just as confused. The good news is that it seemed to only happen in a few areas (maybe eight holes on the HS skin). The flush set is smooth and the dimple dies look perfectly formed to me, so all I can guess is that a few of my clecos have an edge somehow that is causing the deformities.
 
Agree that this is bucking bar damage.

I recently started using a small tungsten bar for tight areas. It is real easy to get a dent using this type of bar. When ever you can use a larger (longer) surface bar as it is easier to keep it parallel to the skin.

Carl
 
To turn the outie to an innie, you migh try putting something solid behind there, such as a bucking bar, and gently tap the pimple down with a plastic mallet. Then, it might even be possible to smooth the surface just a bit more with a flat Nicholson file, being careful not to get too aggressive! I have had pretty good luck with this approach in the past, and the remaining blemish should be easily addresses at painting time. Good luck and build on,
Jim
 
I recently started using a small tungsten bar for tight areas. It is real easy to get a dent using this type of bar. When ever you can use a larger (longer) surface bar as it is easier to keep it parallel to the skin.

That's interesting. I only have the one tungsten bar that I've used so far; for the most part, I like it, but I don't have anything to compare it to. It seems like, excepting odd locations, everything I'd read had been that the tungsten was the bees' knees...maybe I'll have to consider adding to my tool collection...
 
To turn the outie to an innie, you migh try putting something solid behind there, such as a bucking bar, and gently tap the pimple down with a plastic mallet.

I wouldn't have thought that would have enough force...good to know that this is a viable approach. I'll give it a go the next time I'm in the shop. I've long ago given up on building a perfect airplane...just want a safe one.
 
Can we see the bucking bar. Mine had very sharp edges and corners, so I radiused them with the grinder and abrasive cloth.
 
We had a similar issue on our wings. When closing out the wings you end up with your arm stuck way in there bucking, and a couple times I fumbled the bar. No big deal until we turned it over and saw the pimples on the top skin. :( We learned the hard way to wrap the bar and/or lay a towel in there.

BTW, it's pretty hard to see those bumps when whipping by at 200mph, blasting out of short strips, and doing fingertip aileron rolls. Don't sweat it. Your plane will still be 99.99999% awesome! :)

DEM
 
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