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Flush Riveting Skins

J

Jarrett

Member
Started riveting the side skins on my 14A tailcone today! I've been able to get into a pretty good rhythm as far as setting the rivets, but I'm having some problems with deformation around the holes. Before, the rivets go in there is only a slight deformation around the hole, however once set it seems to become way exaggerated (Atleast that's what I see). The shop heads are being set very nicely, so it's not a structural issue, however this deformation it's driving me crazy! To make it even stranger, I've had to drill out a couple of rivets and the second they are out of the hole the deformation seemingly dissapears and it returns to the previous state... I'm using a rubber flush set with a tungsten bucking bar (for the most part) and tomorrow I'm going to try and get help with the bucking bar. I have a few bumps here and there, but most of the vast majority of these holes are bump/dent free (I think). I've also noticed a similar effect on some squeezed rivets in the longerons so is it just due to the nature of the skin? I'm not sure if this is normal as I've seen builders with similar results, but I want to get rid of this if at all possible. I don't think it's a dimpling problem as before the rivets go in it's fine, but maybe does adding a rivet exaggerate the deformation? I've never had this problem with riveting before so I'm a little lost! Once the plane is painted will this deformation be evidently visible or will it mainly disappear? I've only done half of one side of bulkeads and part of the middle J-Stiffener so I want to try to figure this out before moving forward. Thanks!
https://photos.app.goo.gl/6qwcXts2sGDE3Ahd6
https://photos.app.goo.gl/uvn75RknDTMUeoKi8 (Before Rivets)
https://photos.app.goo.gl/YWWpgQbYNTdLLrdX7
https://photos.app.goo.gl/sa6neejQR6aKLU869
https://photos.app.goo.gl/HWeRT63UpL9bpXe28
 
Last edited:
Underdimpled

My opinion...
Looks like underdimpled holes. It's called pillowing.
What dimple tool was used?
 
Push it out

The skins look under dimpled to me.

You might be able to adjust the existing rivets; Take a back rivet set, or similar tool (I used a hard wooden dowel), place on the shop head of the rivet and give it a moderate "whack" with a lightweight (12oz) hard plastic mallet -- observe result, adjust level of "whack."
 
Under dimpling is the #1 issue that I find with new builders. My recommendation for all new builders is to find someone locally who has building experience who can help you out at the beginning.

New builders may deny that it's a problem. 'Looks ok to me' is not the same as 'Looks ok'. They say 'I spent a lot of money on my hydroformulator watzit' for dimpling, it must be right'. Not. It's more about builder technique and tool adjustments, both of which need experience and/or mentorship.

V
 
Jarrett said:
Started riveting the side skins on my 14A tailcone today! I've been able to get into a pretty good rhythm as far as setting the rivets, but I'm having some problems with deformation around the holes. Before, the rivets go in there is only a slight deformation around the hole, however once set it seems to become way exaggerated (Atleast that's what I see). The shop heads are being set very nicely, so it's not a structural issue, however this deformation it's driving me crazy! To make it even stranger, I've had to drill out a couple of rivets and the second they are out of the hole the deformation seemingly dissapears and it returns to the previous state... I'm using a rubber flush set with a tungsten bucking bar (for the most part) and tomorrow I'm going to try and get help with the bucking bar. I have a few bumps here and there, but most of the vast majority of these holes are bump/dent free (I think). I've also noticed a similar effect on some squeezed rivets in the longerons so is it just due to the nature of the skin? I'm not sure if this is normal as I've seen builders with similar results, but I want to get rid of this if at all possible. I don't think it's a dimpling problem as before the rivets go in it's fine, but maybe does adding a rivet exaggerate the deformation? I've never had this problem with riveting before so I'm a little lost! Once the plane is painted will this deformation be evidently visible or will it mainly disappear? I've only done half of one side of bulkeads and part of the middle J-Stiffener so I want to try to figure this out before moving forward. Thanks!
https://photos.app.goo.gl/6qwcXts2sGDE3Ahd6
https://photos.app.goo.gl/uvn75RknDTMUeoKi8 (Before Rivets)
https://photos.app.goo.gl/YWWpgQbYNTdLLrdX7
https://photos.app.goo.gl/sa6neejQR6aKLU869
https://photos.app.goo.gl/HWeRT63UpL9bpXe28
Click to expand...

I must agree that from the "before rivets" photo the skin does look under dimpled. But it is hard to judge in just one photo. However if it is getting a lot worse after riveting then look at the substructure. If you used a squeezer to dimple the sub structure then was it correctly set up? Squeezers do tend to under dimple, but you'll need to set it to get the best dimple you can. Chronic under dimpling of substructure may show through thin skins.

Seeing any deformation on skins that appears after riveting points to substructure problems. More commonly you'll see this on poor joggles or too sharp transitions between flange sections on nose ribs and curved bulkheads.

I'm not familiar with the -14 but it's possible these skins are thinner than what you've worked with before which could make the problem more apparent.
 
Vinyl interference?

Here's a few other ideas:

I am not sure if this is an issue in your case. It looks like the vinyl strips that have been removed may be too narrow or too close to the rivet heads for the flush set to fully and evenly contact the rivet head.

Also I suggest checking that parts are clecoed together tight, before riveting. Use lots of clecoes, as in every other hole. In the photos there are definitely not enough clecoes, it should look more like a porcupine!

A short piece of rubber hose on the rivet tail, under the bucking bar, can also help hold the parts together while making the shop head.
 
Last edited:
Back-Riveting Saved Me :)

Appreciate all the help gents! I definitely agree that the holes were slightly under-dimpled, so I'll make sure to fix that for next time. I made sure to really go over all of the substructure components and I even used a substructure die for each substructure. Also when riveting in the future and particularly with parts that can't be back-riveted I'll make sure to use more clecos. I started doing some more research on my riveting technique/equipment and found that A the mushroom set I used isn't used too much (its a non-swivel mushroom set and I haven't found too many builders that use it) and B back-riveting is often preferred as it's a lot easier and gives more consistent results. With this in mind I went and got some foam mats and cut a spot for my back-riveting plate using paper to shim it up. I completed most of the first j-stiffener with it and there is no additional deformation. Yay!! :) With this is mind I am happy that I can get better results, however I'm wondering what kind of set I could use moving forward. I'm going to try riveting with a partner next time so I can really focus on keeping the set perpendicular and steady (I believe this caused the extra deformation). I'm most likely going to get a flat mushroom set (no rubber) and also a swivel set which I have seen used extensively (any other suggestions?). I'm also going to be meeting with another builder that has built an RV-8 to get some more tips. Lastly, after the plane is painted how visible will any dents or deformations be visible? There is one spot on the skin that I managed to put a little more deformation which I believe it is due to a small dent. Will the painters be able to remove this by smoothing out the area with some sort of filler? Thanks!
 
For me, back riveting is the answer wherever possible.
Then the next option is the swivel set.
The small non swivel mushroom IMHO gives the best results, especially on curved bulkheads but it requires absolutely perfect technique. The slightest lapse will be obvious. A partner I think is a must for this one. Its taken almost 3 planes for me to be happy pulling that one out of the drawer. Starting with it is ambitious.

I wouldn't stress too much, it will look a lot better with paint rather than reflective Alum.

Good luck
 
Jarrett said:
Appreciate all the help gents! I definitely agree that the holes were slightly under-dimpled, so I'll make sure to fix that for next time. I made sure to really go over all of the substructure components and I even used a substructure die for each substructure. Also when riveting in the future and particularly with parts that can't be back-riveted I'll make sure to use more clecos. I started doing some more research on my riveting technique/equipment and found that A the mushroom set I used isn't used too much (its a non-swivel mushroom set and I haven't found too many builders that use it) and B back-riveting is often preferred as it's a lot easier and gives more consistent results. With this in mind I went and got some foam mats and cut a spot for my back-riveting plate using paper to shim it up. I completed most of the first j-stiffener with it and there is no additional deformation. Yay!! :) With this is mind I am happy that I can get better results, however I'm wondering what kind of set I could use moving forward. I'm going to try riveting with a partner next time so I can really focus on keeping the set perpendicular and steady (I believe this caused the extra deformation). I'm most likely going to get a flat mushroom set (no rubber) and also a swivel set which I have seen used extensively (any other suggestions?). I'm also going to be meeting with another builder that has built an RV-8 to get some more tips. Lastly, after the plane is painted how visible will any dents or deformations be visible? There is one spot on the skin that I managed to put a little more deformation which I believe it is due to a small dent. Will the painters be able to remove this by smoothing out the area with some sort of filler? Thanks!
Click to expand...

Awesome! When back riveting you don't necessarily need to use the back rivet plate if you have one of these https://www.cleavelandtool.com/prod...7&_sid=3194a14cd&_ss=r&variant=18378216800318 to use with a partner.

Also when you get to wing top skins something like this https://www.cleavelandtool.com/prod...5&_sid=3194a14cd&_ss=r&variant=18378216734782 or this https://www.cleavelandtool.com/prod...8&_sid=3194a14cd&_ss=r&variant=18686647435326 will help you back rivet in more places.

Also if you haven't already Mike Lauritsen's videos on dimpling using C frame and squeezer are excellent https://www.youtube.com/watch?v=Um_eVYw7N2M&t=267s and https://www.youtube.com/watch?v=_mpbsQF1eu0&t=9s
 
Most replies mention under-dimpling and I agree this could be your major issue. You don't mention what method you're using and this would be helpful to better diagnose your issue and offer a solution.
 
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