Basic building skill question

[PipeDreamer]

I have a question that's bugging me a lot and I tried googling it and searching to no avail perhaps because the right terminology is eluding me.
The questionis : when the skin is riveted and its surface looks warped or distorted around the rivet whats is it called ?
I want to learn how to achieve commercial quality finished surface. A lot of good examples here, so obviously it is doable but what is it called?
Would appreciate references, links, etc.

[BillL]

I don't know of a specific name for it, but assume like a concave area centered on the rivet? If there is some picture of one it will help all identify the issue and propose corrective actions.

Sometimes it is due to the underlying part as it is below grade and may need a shim. It may be an over driven rivet, air pressure too high or driven too long with too little bucking. There are little circles created with dimpling tools, but mostly cosmetic.

Post a good picture and stand back, the information flow will be unleashed.

[rv7charlie]

If it's actual damage to the skin, from the rivet set, for instance, most people call the damage a 'smiley', because the mushroom set will leave a 'smile' shaped arc if you let the gun get too far from perpendicular.

If you're talking about a properly set rivet (in a dimpled hole), but you can still see what appears as a slight concave appearance around the rivet, I don't have a name for you, but it's caused by not creating a crisp dimple before riveting. Many people fear damaging the skin, and under-dimple. Several will no doubt recommend a multi-hundred dollar tool to cure it (which works great if you don't mind spending the money), but you can get the same results with a simple C-frame & a rubber mallet. Just hit the die holder harder. To expand your comfort zone, play with some scrap & hit the die holder with a fat rubber mallet like you were driving a big framing nail. (I usually strike one medium force blow, which forms the dimple maybe 3/4 of the way, then hit it again, hard.) I'll bet you can't actually damage the skin using a rubber mallet on the die holder. Goal is a sharp transition from dimple to surrounding skin. If properly dimpled, you shouldn't be able to catch a fingernail on the edge of the head after riveting. If under-dimpled, you can.

I think Cleveland Tool has a youtube video showing how to detect under-dimpling.

Hope that helps,

Charlie

[agirard7a]

I believe "deflection" is the term. It can also be from under dimpling
the skin. A good wack on a solid surface with the C frame dimpler and a good quality dimple die will make for flat skins. 35lbs with a 3 x gun is enough pressure for 3/32 rivets. Go lightly with the rivet gun. It doesn't take much to get the correct shop head.. If you dimple with the pneumatic squeezer, it often fails to make crisp, non-deflected dimples in the skin.

[PipeDreamer]

None of it seems to be relevant to riveting itself, it is more of distortion of skin where it is riveted to whats under, warping sized from a penny to silver dollar size or more. It is what makes home build look like a home build. Perhaps it is what can be covered with bondo, but it sure will take a lot of bondo to fill all of it when its bad.

[PipeDreamer]

This is a minor case obviously. Is there a definition for it?

[PipeDreamer]

This a "good" example

[rockwoodrv9]

A friend of mine who is helping me finish my 9A has a beautiful 4 and 6. His wings look like glass. He used 3m epoxy to glue the skin to the ribs, cleco them together, let it dry, then rivet. I used the same technique on the access panels on the foreskin of my plane and it worked well.

If I was building again, I would epoxy the skins on the tops of the wings to keep them smooth. I may add a few ounces, but not more than skipping breakfast before you fly. I would not do the underside of the wings - if anyone crawls under the wings to check I am OK with a few dimples there.

[slngsht]

I don't know what it is called either, but it is caused by being too gentle when dimpling. My first rudder skin was like that. I posted it here and someone told me what the problem is and what the proper results look like, so I redid the part and all is good.

[60av8tor]

Originally Posted by PipeDreamer

This is a minor case obviously. Is there a definition for it?

Hard to tell what your picture is showing - longeron? If so, that should be fairly easy to get them all looking like the rivets to the left of the ugly ones that are circled. Like the others have said - either under dimpling or a shim needed. My guess is under dimpling. I've seen examples of folks that had no clue they were under dimpling - looked like they riveted using a ball-peen hammer. Not pretty. I used a c-frame for my entire airframe - even though I own a DRDT - and I wasn't very gentle with it. Most of my rivet lines are very flat. I'm a fan of the c-frame and rubber mushroom set for solo riveting.