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Rivet Lines In Skin

rjm727

Well Known Member
So, I have been very bothered by the rivet lines showing up in my skin (particularly on the HS at this time). There doesn’t appear to be any real “pillowing” of the skin but the rivet lines are slightly indented in the top of the HS. It has been bothering me but the more I look around the more I see this. I have even noticed it on my day job A320! Based on that, I am guessing it is somewhat inevitable. That being said, I would like to minimize this going forward (almost done with tailcone and I’m not seeing it there yet (fingers crossed). Any tips or tricks to minimize this? I’ll try to find a pic to post.
 
If you dimple, you will get this. Even the best spring back dies are not perfect. Dies form the dimple by stretching and displacing the metal.
Some in the past took the drastic measure of glassing over, or filling, the rivets lines. Very bad idea! Run from one of these airplanes!

Art Chard used to machine countersink everything to avoid this. If you have ever seen one of his builds, you would know what quality is.
....But, unless your Art Chard, and have mad skills......

All that said, what are you using to dimple with? What is your set up? This can make a big difference but you will still get some pillowing. I personally like that look. It more closely approximates fabric aircraft in our old rag wings. I think it looks like an airplane should, but that is just me.
 
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just me

For me I found this happens more if my air pressure is too high, or if the bucking bar is not a tungsten or other heavy bar.

I turned down the air pressure and adjusted (opened) the regulator on the gun. Others say the regulator does not matter, but It does for me.
I found in general, the more hits the gun takes to set the rivet, the less chance I found this happening. But too many hits, and the rivet will harden and will never set. about 3 seconds seems to be max.

There are other opinions out there, and I could be off base, but that is what worked for me.

But on the thin skins with thin ribs, this is gonna happen.
 
Are you using a 3X gun instead of a 2X? What pressure? Proper bucking bar technique? Straight flush set instead of a swivel flush set?

Carl
 
Thank you for the response. I am using a DRDT2 to dimple skins with Cleveland dies. I’m sure it won’t be as bad once it is painted. Right now it looks like a bad mirror…lol

If you dimple, you will get this. Even the best spring back dies are not perfect. Dies form the dimple by stretching and displacing the metal.
Some in the past took the drastic measure of glassing over, or filling, the rivets lines. Very bad idea! Run from one of these airplanes!

Art Chard used to machine countersink everything to avoid this. If you have ever seen one of his builds, you would know what quality is.
....But, unless your Art Chard, and have mad skills......

All that said, what are you using to dimple with? What is your set up? This can make a big difference but you will still get some pillowing. I personally like that look. It more closely approximates fabric aircraft in our old rag wings. I think it looks like an airplane should, but that is just me.
 
Thank you sir. I’m using a 2x most of the time on the smaller rivets on the skin. Air pressure is approx 38psi. I’ll play with that a little. I’m learning it is a fact of life but would like to reduce it as much as possible.

Thanks again!

For me I found this happens more if my air pressure is too high, or if the bucking bar is not a tungsten or other heavy bar.

I turned down the air pressure and adjusted (opened) the regulator on the gun. Others say the regulator does not matter, but It does for me.
I found in general, the more hits the gun takes to set the rivet, the less chance I found this happening. But too many hits, and the rivet will harden and will never set. about 3 seconds seems to be max.

There are other opinions out there, and I could be off base, but that is what worked for me.

But on the thin skins with thin ribs, this is gonna happen.
 
On the smaller rivets I am usually using a 2x gun set at 38psi. Smaller and less fatiguing but I do have a 3x as well. I’m using the Cleveland flush set with the rubber footing and it is a swivel. I have three different tungsten bars.

Are you using a 3X gun instead of a 2X? What pressure? Proper bucking bar technique? Straight flush set instead of a swivel flush set?

Carl
 
A fix -- perhaps...

You may find that a small block or dowel made of hard wood placed over the shop head and then 'smacked' with a nylon mallet (not tapped, not whanged...just smacked) will un-dent the rivet and surrounding area...
 

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Dimples

Post a photo please.
From the description, it sounds like "under dimpling".
Looks like a mirror with a distortion around each dimple.
 
There are a number of factors that can have an influence on causing what you have described, but a fairly common one is the actual dimpling process itself. The thicker skins of the horizontal stabilizer and elsewhere amplify the possibility of
Dimples, not being formed as well as they could be. Particularly with the tool that you are using.
The riveting technique can also have an influence as well. Combine issues from both and the finish can definitely look far from what some people would prefer.
 
I will post a photo tomorrow. I don’t believe that it what it is, I know what that looks like. It is more a line than individual rivets. If you look down the skin you see an indentation (line) at each rib. The skin in between does not “pillow” up, but each rib is visible. I’m sure I have done something to cause it, but I don’t know what and it seems to be a common thing (even on the manufacturer built A320). I’ll get a pic on here as soon as possible and let me know what you think. Thanks for the response.

Ray

Post a photo please.
From the description, it sounds like "under dimpling".
Looks like a mirror with a distortion around each dimple.
 
Hmm, ok, so you think the DRDT2 could have that affect, interesting. The last response suggested it could be under dimpling but I didn’t think that sounded plausible because of the DRDT2 but what you both suggest makes sense. Also might explain why I hadn’t seen it on any other surfaces yet. I would definitely like to rectify before the wings. So, would you recommend a c frame for the thicker skins?

There are a number of factors that can have an influence on causing what you have described, but a fairly common one is the actual dimpling process itself. The thicker skins of the horizontal stabilizer and elsewhere amplify the possibility of
Dimples, not being formed as well as they could be. Particularly with the tool that you are using.
The riveting technique can also have an influence as well. Combine issues from both and the finish can definitely look far from what some people would prefer.
 
Hmm, ok, so you think the DRDT2 could have that affect, interesting. The last response suggested it could be under dimpling but I didn’t think that sounded plausible because of the DRDT2 but what you both suggest makes sense. Also might explain why I hadn’t seen it on any other surfaces yet. I would definitely like to rectify before the wings. So, would you recommend a c frame for the thicker skins?

My preference is the c frame, but the important thing is to learn to evaluate a dimple quality and then adjust or make corrections as needed. Dimple quality can be evaluated by analyzing the reflection in the surface of the skin. Some people are able to tell just by looking at the reflection of overhead lights in the vicinity of a dimple, but for others, it is easier if they use something like a grid on a piece of graph paper held near the skin, so that you can see the grid reflection in the skin surface. A good quality dimple should have no distortion in the reflection, except for with in the inside of the temple. The reflection adjacent to the edge of the dimple and in the surrounding area should be nearly as distortion free as it is out in the middle of the skin where there are no rivet holes. I say, nearly, because many of the spring back dimple dies, will actually form a very slight protrusion into the skin around the perimeter of the temple, but that is not an issue, because it generally disappears when you set the rivet.
 
Im no genius or experienced builder so i cannot say what is right but I can tell you what I have done and it may help.

I use the DRDT....it must be adjusted correctly...you almost cannot over dimple...make sure the frame flexes when applying pressure...the dimples will show a slight line under light emanating from the dimple but i consider this normal now...its because you are stretching the material...BUT...you can only see this if "looking down the line" under a light. The DRDT works. Now disclaimer on the DRDT. I was given the tool to fit on the end of my home made DRDT frame...my frame is thicker than the manufacturers. You have 4.76 mm (or whatever the **** that is in imperial) and I used 6mm thick material. so my frame will flex less than yours. I spent a fair few hours Dicking around with it and shimming the base so i could ensure the dimple dies came together perfectly when the frame is at full flex....maybe the c frame is more fool proof I dont know I have not used one but i imagine you could easily underwhack a few dimples with the c frame as you are relying on the same hit each time...my dimples are consistently the same as I move the handle to the stop....

Secondly I use 34 psi on a brand new Sioux 2 x with a swivel flush set...blue tape applied regularly changed on flush set.

I used a matchbox sized tungsten bar here from cleveland tools.

I use cleaveland tools dimple dies (all sets)

I have taken down the line type pics to see if yours is same...it might help.you can see minor distortions if you look hard but once painted I believe this will show almost nothing. When I dimpled I noticed the lines out from the dimples...I tried more and less dimpling pressure on the drdt. Nothing made any difference until I went too light then I saw ugly dishes appearing from under dimpling...I see a lot of that on pics on line...I felt on the DRDT on thin skins you can almost stretch the material too much and over dimple but it takes a lot...The HS 32 thou skins need a good bit of pressure to dimple nicely. Oh and when you pull the trigger on your 2X gun...(and that is all you need for 3/32!) keep the pressure on the head of the rivet and the tungsten on the shop head...UNTIL...you have released the trigger....or a good whack without the tungsten on the shop head and or the mushroom coming off the manufactured head means the jackhammer you have sitting on your pretty skin is keen to whack a smiley in it....especially with more pressure at the inlet of the gun. tip, inner and spar fitted with cleaveland tools flat sets on the cleaveland pneumatic squeezer using a 1.5" no hole yoke (plus a few other yokes for various rivets) and blue tape on the flat set.

BTW...technique matters. Hold the flush set to the surface firmly..let the tungsten bounce on the shop head.
 

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