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  #1  
Old 01-25-2018, 02:29 PM
Mlidzct Mlidzct is offline
 
Join Date: Nov 2016
Location: Southington, Ct
Posts: 86
Default Gap around flush rivet mfg head

I started my project with mainly used/borrowed tools from a friend and have been adding tools of my own as I go along. The dimple dies I was using were giving good results but they have built a whole airplane already and I figured why not get a new set of my own. I bought the Cleveland spring back dies to use on the skins. I also bought a set of the sub structure dies just to try it out. I tried on a scrap before going to town and everything appeared to look good. I went ahead and dimpled real parts and during assembly I started noticing a slight gap around the manufactured head of the rivets that I wasn't getting before with the old dies. I was pretty concerned so I took some scrap, made a test part, and took a cross section of the joint on a wire EDM machine I have at work. I think the joint looks OK (other than the shop head being a little off) but you can see the little gaps around the head. It looks like the new dies leave a larger radius and is the reason for the gap.

What is everyones thoughts on the gaps I am seeing? Could there be a different reason this is happening?

https://drive.google.com/file/d/1pfU...ew?usp=sharing

https://drive.google.com/file/d/1IMw...ew?usp=sharing
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Last edited by Mlidzct : 01-25-2018 at 09:53 PM.
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  #2  
Old 01-25-2018, 04:19 PM
tims88 tims88 is offline
 
Join Date: Jul 2016
Location: Arvada, CO
Posts: 122
Default

I've seen the same thing with my Cleaveland dimple dies, which I've used for all of my empennage work so far. Some older dies that I'm borrowing from another builder create dimples that don't leave that small gap around the edge of the rivet head. From what I've read on here it doesn't seem to be a structural problem, but I've been wondering if anything weird will happen when it comes time to paint.

Here's another thread discussing the same thing: http://www.vansairforce.com/communit...d.php?t=152064

It's awesome seeing such a clean cross section in that picture!
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  #3  
Old 01-25-2018, 08:24 PM
vluvelin vluvelin is offline
 
Join Date: Dec 2013
Location: Montreal
Posts: 218
Default

Avery dimple dies fix the problem
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  #4  
Old 01-25-2018, 09:26 PM
Mlidzct Mlidzct is offline
 
Join Date: Nov 2016
Location: Southington, Ct
Posts: 86
Angry Discovery

Sorry I cant seem to embed the pics into my posts...

https://drive.google.com/open?id=1va...ww-7LshyvtBKdi

The old dies on the left are unkown make but believe to be avery.

The dies on right are my new cleveland spring back dies.

I measured the angle on the male dies using an optical comparator and the old dies are 98 degrees. The cleveland male die also measures 98 degrees which is a little sharper than the 100 degree rivet which is what you want to compensate for spring back.

Edit: I took measurements of the female dies using a CMM machine. Both sets have roughly the same angle. The old dies have a smaller diameter at the face than the cleveland dies (0.018"). I believe the female end is too big on the cleveland and so a larger radius is formed at the top of the dimple which leaves the noticable gap.
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Last edited by Mlidzct : 02-07-2018 at 09:15 AM.
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  #5  
Old 01-25-2018, 09:39 PM
Mlidzct Mlidzct is offline
 
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Location: Southington, Ct
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Quote:
Originally Posted by tims88 View Post

It's awesome seeing such a clean cross section in that picture!
Yes I was happy how the cross section worked out. I was trying to band saw them but the vibration was making them fall apart. The wire edm cuts by eroding the metal with an electric arc. The width of the cut is only 0.010” and puts no force on the work since the electricity is doing the work.

After reading your comment I made up two test strips and gave them a coat of white rustolem spray paint just to see what it would look like. The paint didnt bridge the dimple to rivet in either case, and honestly they look about the same painted. Im sure after a real paint system is applied there would be no visual difference. My concern is more structural, I think the cross section illustrates the interface on the factory side still looks more solid than the shop head even with the gap present.

https://drive.google.com/open?id=1ty...SlsqX4YGdvq6Ce
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Last edited by Mlidzct : 01-25-2018 at 09:42 PM.
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  #6  
Old 01-25-2018, 09:48 PM
Mlidzct Mlidzct is offline
 
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Location: Southington, Ct
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Default Wanted to know why

Quote:
Originally Posted by vluvelin View Post
Avery dimple dies fix the problem
I saw that was your fix in the other thread but I am the type of person that needs to know why. I was also trying to find a way to fix the skins I already dimpled. Interestingly redimpling the hole with the old set didnt improve the gap, but redimpling the hole with mixed matched set does fix the gap. I plan to cross section a sample to see what it looks like before I go and redimple all my holes
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  #7  
Old 01-25-2018, 09:49 PM
BillL BillL is offline
 
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Excellent work, you should share that with Cleaveland. They seem to to truly be interested in making excellent tools.
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  #8  
Old 01-26-2018, 08:46 AM
Mlidzct Mlidzct is offline
 
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Location: Southington, Ct
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Default I tried

Quote:
Originally Posted by BillL View Post
Excellent work, you should share that with Cleaveland. They seem to to truly be interested in making excellent tools.
Last Sunday when I noticed the problem I emailed some pics to Cleveland's general mailbox. I hadn't heard back so forwarded the message and pics to Mike at Cleveland yesterday morning and still nothing. So I'm not sure they are getting my emails.
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  #9  
Old 01-26-2018, 10:11 AM
Aluminum Aluminum is offline
 
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Location: San Jose, CA
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Keep in mind that the results will be slightly different on skins of different thickness. A die that produces perfect results on thin tail skins won't look as good on thicker fuse skins.

On test coupons my Brown and ATS dies systematically produced dimples too deep, as in daylight showing under a ruler placed over the rivet. Cleaveland didn't have this problem. On tailcone side skins, however, I found Brown dies to produce the most esthetically pleasing result. Structurally it's all the same.

I'm a little surprised that the CNC army on here hasn't yet posted G-code to produce custom dies to match every situation: put round stock in a collet and clamp a lathe bit in a vise on a Tormach, insta-dies! Too bad my local makerspace went bankrupt...
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  #10  
Old 01-26-2018, 05:36 PM
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zilik zilik is offline
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I saw this when I was building 20 years ago so I started lightly countersinking my dimples. Problem solved and the plane is still flying. While it adds to the work involved the rivets seat nicely.
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