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New Builder: Am I doing something wrong here?

ReidW

ReidW

Member
Hi folks,

I recently got the workshop all set up, practice kits completed, and am starting to put rivets in the real thing. I spent a lot of timing getting my dimpling setup and technique just right so that the areas around the dimples have no distortion whatsoever, but I’m starting to put in the flush rivets on the VS and am a bit worried I’m doing something wrong. Prior to shooting the rivet there is no distortion but afterwards it looks like the river has pulled the skin just a bit tighter than the clecos could and the result looks like a bit of a dent/concave region around each rivet.

I’m using a mushroom set and a tungsten bucking bar, being as careful as possible to not let the mushroom set move or bounce. Pressure is set such that it takes 3-4 seconds to set each one.

I don’t have a buddy close by to compare with what it ought to look like and I haven’t seen one up close in a while so it’s likely I’m just being OCD, but thought I’d ask the experts before I get too much further. Thanks!IMG_7420.jpegIMG_7421.jpeg
 
I was a perfectionist too - now that I'm on the finishing kit of my 9A, I've been cured of that! :p It honestly doesn't look bad in the pictures. Go look at most planes on the flight line and you'll see they all have it somewhere.

In my limited experience, I've found that one cause of this is if the angle of the underlying flange isn't parallel with how the skin should set (or the flange sets lower than it should), causing the rivet to pull the skin down to meet the flange. It's not that you're pounding on the rivet funny or anything. Some parts, especially those that attach to ribs, just have a tendency to do that if the parts aren't sized/mated perfectly. Take a look at some completed wings and you'll see that a lot of them have this effect at the rib rivet lines.
 
skelrad said:
I was a perfectionist too - now that I'm on the finishing kit of my 9A, I've been cured of that! :p It honestly doesn't look bad in the pictures. Go look at most planes on the flight line and you'll see they all have it somewhere.

In my limited experience, I've found that one cause of this is if the angle of the underlying flange isn't parallel with how the skin should set (or the flange sets lower than it should), causing the rivet to pull the skin down to meet the flange. It's not that you're pounding on the rivet funny or anything. Some parts, especially those that attach to ribs, just have a tendency to do that if the parts aren't sized/mated perfectly. Take a look at some completed wings and you'll see that a lot of them have this effect at the rib rivet lines.
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That's about what they should look like - you're fine, build on.
 
Reid, welcome to VAF :D

Agree with posts above, try upping pressure a bit, but they really do not look too bad.
 
What size mushroom set?
It does look like maybe the set is leaving a dimple. Nothing wrong, but if your a perfectionist, you want to figure it out.
 
I transferred my RV riveting skills to building Cessna wings, stabilizers, and flight controls. I exclusively use a 4X gun and ditched my 2X and 3X. It’s all about air pressure and trigger control. Unless you back rivet it’s almost impossible to not get a small amount of distortion around the rivet heads. You will be fine as long as you don’t jack hammer the rivet.
 

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Thanks for the words of encouragement all. I'll bump up the pressure a little and carry on.

Larry, it's a 1" mushroom set. Has a nice polish and is slightly convex which is how I understand it is supposed to be. It's the one that comes in the kit with the red box 3X gun I have. I'm not opposed to trying a different one if folks think there is a better one, I just don't have another one in hand.IMG_7422.jpeg
 
ReidW said:
Thanks for the words of encouragement all. I'll bump up the pressure a little and carry on.

Larry, it's a 1" mushroom set. Has a nice polish and is slightly convex which is how I understand it is supposed to be. It's the one that comes in the kit with the red box 3X gun I have. I'm not opposed to trying a different one if folks think there is a better one, I just don't have another one in hand.
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Odd. That's a common set. Ok.
What pressure?
Regulator or Flow restrictor?
2-3 seconds is the sweet spot.
Is it possible the last hit is after the bar is removed? That would do it.
 
Appreciate the help! To me what Brandon said above about the flange not being quite parallel with how the skin wants to sit seems to maybe make the most sense looking at it. It does seem to be getting better the more rivets I put in. The latest rivet in the line looks the worst until I put the next one in and then it straightens out a bit like it's just the skin trying to pull away a bit causing the distortion. The extremely narrow lights I have in the shop just make any distortion painfully obvious.

90psi to the gun with the brass regulator/flow restrictor at the gun. I did bump the pressure up a click such that the rivet sets in around 2 seconds and that seems to have helped a bit too. Definitely not removing the bar/gun before finger off the trigger. Learned that mistake on the practice kits.IMG_7423.jpegIMG_7424.jpeg
 
I used the same mushroom set for 90% of my skin rivets. I like to use a regulator dedicated to the rivet gun only. I also like using a 2x gun Sioux gun - I can control it better and for me it has better "feel", and for 90% of rivets it's plenty. For AN3-3.5 rivets usually around 20-25 psi at the regulator, with no in-line restrictor, works for me. Bucking bar is important - tungsten bars are best. Also fixing the work pieces in place is important. Regulator (larger version): https://blogger.googleusercontent.c...BP8RzFPdjLbKfjDyiO_kllHqw/s4032/IMG_1962.jpeg

All that said, your rivets look fine - the minor depressions you see now won't show much if at all when it's painted.
 

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mturnerb said:
I used the same mushroom set for 90% of my skin rivets. I like to use a regulator dedicated to the rivet gun only. I also like using a 2x gun Sioux gun - I can control it better and for me it has better "feel", and for 90% of rivets it's plenty. For AN3-3.5 rivets usually around 20-25 psi at the regulator, with no in-line restrictor, works for me. Bucking bar is important - tungsten bars are best. Also fixing the work pieces in place is important. Regulator (larger version): https://blogger.googleusercontent.c...BP8RzFPdjLbKfjDyiO_kllHqw/s4032/IMG_1962.jpeg

All that said, your rivets look fine - the minor depressions you see now won't show much if at all when it's painted.
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Same here.....2X gun and about 20-30 PSI on flush rivets but AN470 rivets more pressure is usually required. You're doing good so just build on.
 
Bearman said:
Same here.....2X gun and about 20-30 PSI on flush rivets but AN470 rivets more pressure is usually required. You're doing good so just build on.
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Bearman is correct. I always count trigger bursts. Depending on the rivet size and line pressure, some rivets will take 8- 10 trigger bursts.. This method gives very consistent results
 
Couple things to try
-Swivel mushroom set. Many hate them. I like it.
-Regulator at or near the gun. I use a pigtail. Mini Harbor Fright works fine. I use a RTI mini. Set to 22psi for #3 and 30psi for #4.
There's a few dings.
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Practice feathering the trigger. Start with a couple light hits then finish with a couple heavy hits. Easier to control the set from wondering that way.

The guys in the Van’s prototype shop have said they don’t know (or care) what the line pressure is (probably 90psi). They make their adjustments at the regulator on the gun. I’ve done the same combined with the technique above.
 
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Thanks for all the help and great suggestions! As much as I'd love a Lindy I want more to finish the airplane by the end of the decade so I went ahead and set the rest on the VS last night. Overall I'm happy with the results, though it isn't perfect. On the next skins I do I'll buy the RTI regulator to put on the gun instead of the brass one and try the flush set PhatRV mentioned in case that makes a difference. Until then I shall build on. We'll meet again here, same time only with a new problem I haven't gotten to yet :)
 
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