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  #1  
Old 02-21-2013, 09:29 PM
Mike Buckler Mike Buckler is offline
 
Join Date: Aug 2012
Location: Chatham Ont.
Posts: 34
Default My First Row Of Skin Rivets. Is The Gap Normal

I am a first time builder. Started riveting the top skin on tonight after putting in the first 10 rivets I started checking my performance. I found that the skin is bent in at the rib there is no noticeable dents anywhere. Also I didn't feel that I was pushing hard at all.
First time trying to post an image so I hope this works.

The above image is just to show how I laid an aluminum bar against the skin.


See the gap behind the bar where the rivets are. Is this normal should I be concerned? Am I pushing too hard on the rivet gun? Or just being too fussy.


The above image is just to show that when I moved the bar over a rib that had not been riveted there is no gap at all.

Thanks in advance any and all help will be appreciated.
Mike
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  #2  
Old 02-21-2013, 10:13 PM
Stalldog Stalldog is offline
 
Join Date: Oct 2011
Location: Kansas
Posts: 331
Default

Dumb question, but did you dimple the ribs with the same dies as the skin?
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  #3  
Old 02-21-2013, 10:37 PM
wfinnell wfinnell is offline
 
Join Date: Jun 2006
Location: tucson, az
Posts: 100
Default I had the same problems

Mike,

It is hard to tell from a photo, but it looks to me like your holes may be under-dimpled. I don't see the slight ring around the dimpled hole and the skin surface should be flat right up to the dimple. I can see distortion in the reflection around the holes on the left side of your first photo. If the skin isn't flat before your set the rivet, it won't be after.

I had this problem when I first started, after I figure out how to get a nice crisp dimple the skins are much flatter.

Hope this helps,
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  #4  
Old 02-22-2013, 07:28 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,413
Default

Mike
I see that you are located in Chatham. I live in St Thomas. Do not proceed any further, you need a bit of help. Give me a call 519-631-1369

Tom Martin
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EVO F1 Rocket 1000 hours,
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  #5  
Old 02-22-2013, 08:21 AM
Mike Buckler Mike Buckler is offline
 
Join Date: Aug 2012
Location: Chatham Ont.
Posts: 34
Default

I checked the other wing it is not riveted yet and it is the same.
Thank you all for your help.
MIke
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  #6  
Old 02-22-2013, 08:25 AM
Rupester Rupester is offline
 
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
Default

I've also seen cases where too high of air pressure on the rivet gun can cause the same effect. I have several spots on my plane where the rivets look like the example, because I had increased the air pressure for some 1/8" rivets and forgot to turn the pressure back down.
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  #7  
Old 02-22-2013, 09:31 AM
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gvouga gvouga is offline
 
Join Date: Aug 2005
Location: Raleigh, NC
Posts: 103
Default

A few suggestions...

Rivet gun setting - As others mentioned, too high will cause a larger dip. Even with the proper setting you will see some dip though.

Dimpling - Its hard to tell, but the dimples do look a little rounded in your pictures. I found that using a C-frame and really giving a good whack (techinal term) is the best method to get a crisp dimple. Also make sure you have high quality dimple dies. I've tried dies from both Cleveland and Avery and found them to be good.

Back Rivet - This is by far my favorite method to get smooth consistent dimples. The top wing skins lend themselves to this method very well. The flat bucking bar will rest on the outside skin and the set is used on the shop end of the rivet. Since the flat bar is on the outside of the skin, it creates a very level surface with almost no dip at all. Check one of the major tool suppliers for a long backrivet set and bucking bar. I think I got mine from Cleveland.
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  #8  
Old 02-22-2013, 11:32 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,788
Default

Skin dimples are definetly not fully formed.
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  #9  
Old 02-22-2013, 12:18 PM
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Andrew M Andrew M is offline
 
Join Date: Aug 2006
Location: Secluded Lake,Alaska (AK49)
Posts: 359
Default Power, mass, momentum, stress, strain

A few things to be aware of when setting your pressure and how firmly you hold the rivet gun. A layman's understanding for the purpose of this post; stress is the amount of force that can move metal, but not so much that it permanently deforms. A strain will permanently deform. So the trick is, stress the metal, strain the rivet. Generally, setting pressure at the gun should not be enough by itself to deform the metal, however being heavy handed with the gun can be just enough extra force to start bending metal. This issue presents itself when the gun hits twice and the bar only makes contact once, which can be heard, or an incorrect balance of holding pressures between gun and bar. Now this can be counter intuitive, holding the bar to tight makes you hold the gun to tight, then the bar doesn't get a chance to "bounce" usings its monentum to help absorbe the energy into the rivet, and that energy ends up deforming metal.
A large area flat swivel set helps with this to.
I wouldn't be overly concerned about the quality of work so far. I see this kind of stuff on production airplanes.
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Last edited by Andrew M : 02-22-2013 at 12:55 PM. Reason: clarify definition
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  #10  
Old 02-22-2013, 12:36 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,587
Default A Short Tutorial

Quote:
Originally Posted by Andrew M View Post
Stress is the amount of force that can move metal, but not so much that it permanently deforms. A strain will permanently deform.
Stress is simply force divided by area, with those dimensions, i.e., pounds force per square inch. Stress does not know whether the material being stressed is in its elastic of plastic range of behavior. It's merely a force on an area.

Strain is defined as a movement, such as stretching or compressing, and might either be elastic or plastic. It is caused by stress. Elastic strain will disappear when the stress is removed and plastic strain will, to some extent, remain. For most engineering applications, strain does not have a dimension because the actual strain is commonly presented as divided by the length of the material being strained.

Stress and strain in many materials are related by Young's Modulus, which is simply stress divided by strain, with the strain in its common non-dimensional form. For metals that are not stressed to the point that they yield or deform in a plastic manner, each type of metal has the same Young's Modulus. For most aluminum alloys, it's right around 10 million psi, depending on the alloy. That is, if you put ten pounds force uniformly on a one inch cube, stretching it, it would stretch one millionth of an inch.

Dave
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