VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #1  
Old 06-18-2012, 07:50 AM
bill v bill v is offline
 
Join Date: Mar 2011
Location: zeeland michigan
Posts: 127
Default fuel tank dimple dies

do you use the fuel tank dimple die for both the rib and the skin or would it be wise to use the deeper fuel tank die on the rib and a normal die on the skin? somplace i read that clevland sugests using a deeper die on under skins when you stack three items together so that the top skins set better in the stack of dimples? thanks in advance.
__________________
built rv-4 started 1987 finished 1996 now building rv-7, fitting cowl
Reply With Quote
  #2  
Old 06-18-2012, 09:20 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,358
Default

I'd suggest giving them a flotation test.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #3  
Old 06-18-2012, 09:47 AM
clevtool's Avatar
clevtool clevtool is offline
 
Join Date: May 2006
Location: Boone, Iowa
Posts: 343
Default

Use the tank dies on both the skin and substructure when building the tanks. This allows the proseal to sit under the rivet head without the rivet sitting too high.

On the rest of the airframe you can use the tank dies on the substructure only to allow the normal dimples in the skin to nest better.
__________________
Mike Lauritsen
-
Cleaveland Aircraft Tool
800-368-1822
www.CleavelandTool.com
mike.toolman (at) gmail.com

Like on Facebook - Follow on Twitter - See on YouTube
Reply With Quote
  #4  
Old 06-18-2012, 12:03 PM
dave4754's Avatar
dave4754 dave4754 is offline
 
Join Date: Oct 2009
Location: Edson, Alberta, Canada
Posts: 493
Default Tank Dies?? i didnt realize a specific set were needed?

Is there a special die required for this? I thought to use a standard 3/32 die?


Quote:
Originally Posted by bill v View Post
do you use the fuel tank dimple die for both the rib and the skin or would it be wise to use the deeper fuel tank die on the rib and a normal die on the skin? somplace i read that clevland sugests using a deeper die on under skins when you stack three items together so that the top skins set better in the stack of dimples? thanks in advance.
__________________
Dave Cobb
[color="Red"]=VAF=2019 Donation - and a bit extra for great work![/COLOR="blue"]
Empennage RV 7 - Tipper
Wings complete

Dynon installed and running
Fuse closer to completion, Canopy complete
AME reviewed and repaired O-320-Lyc installed
Reply With Quote
  #5  
Old 06-18-2012, 12:13 PM
clevtool's Avatar
clevtool clevtool is offline
 
Join Date: May 2006
Location: Boone, Iowa
Posts: 343
Default

Quote:
Originally Posted by dave4754 View Post
Is there a special die required for this?...
With the standard dies the rivets will sit about 0.007" above the surface. This is enough to look bad, catch rags... so we designed the tank dies to eliminate this problem. They are .007" deeper allowing for the proseal that won't squeeze out from under a rivet head. Since builders that do the tanks already have the tank dies, we suggest using them on the entire substructure as well, as it eliminates most of the .011" gap between the skin and the substructure.

Links:
http://www.cleavelandtoolstore.com/p...umber=DIE4263T

http://www.cleavelandtoolstore.com/p...mber=DIE4263ss
-
__________________
Mike Lauritsen
-
Cleaveland Aircraft Tool
800-368-1822
www.CleavelandTool.com
mike.toolman (at) gmail.com

Like on Facebook - Follow on Twitter - See on YouTube
Reply With Quote
  #6  
Old 06-18-2012, 01:46 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,077
Default

What's the difference between the substructure dies and the tank dies?

And is there any reason not to use the tank dies generally?

Why were the regular dies designed so that the rivet head would stand proud .007?

Thanks!

Dave
Reply With Quote
  #7  
Old 06-18-2012, 04:18 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,358
Default

Quote:
Originally Posted by clevtool View Post
With the standard dies the rivets will sit about 0.007" above the surface. This is enough to look bad, catch rags... so we designed the tank dies to eliminate this problem. They are .007" deeper allowing for the proseal that won't squeeze out from under a rivet head.
Let's kick a sacred cow.....

Making the dimple 0.007" deeper also increases the dimple's major and minor diameter. For example, a major diameter to match the rivet spec would be 0.1790", while the 0.007" deeper dimple would have a diameter of 0.1957". The geometry means the outer edge of the rivet head is unsupported when squeezed. The edges of the rivet are forced downward as the rivet shank is compressed.



Don't believe it? Take a look at this sectioned rivet taken from a tank made with tank dies. Look close at the shape of the 0.007" "sealant space" under the the rivet head. Now look close at the upper surface...it's not flat. Yep, you won't catch rags on it....not with the edges bent down.



If the rivet is soft and ductile it may be fine. However, we know rivets are not always as ductile as we would like....:



The above photo was taken in my shop at 10x magnification. My own tanks had dozens of rivets like this. As a leak path (or part of a leak path) the crack completely bypasses the sealant under the head. Leak or no leak, it's certainly not good structure.

BTW, go back to the picture of the cutaway rivet again. Note the nested dimples don't have the nice crisp bends of a CAD illustration. It's not the fault of the dimple die, but it does illustrate that the operator is a big factor in dimple QC. A special dimple die doesn't guarantee anything.
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 06-18-2012 at 04:28 PM.
Reply With Quote
  #8  
Old 06-18-2012, 10:35 PM
clevtool's Avatar
clevtool clevtool is offline
 
Join Date: May 2006
Location: Boone, Iowa
Posts: 343
Default

Interesting. Do you have cutaways of the normal dies with and without proseal for comparison. The dimples in this cutaway do not look as crisp as what I would expect from properly formed dimples with good quality dies.
__________________
Mike Lauritsen
-
Cleaveland Aircraft Tool
800-368-1822
www.CleavelandTool.com
mike.toolman (at) gmail.com

Like on Facebook - Follow on Twitter - See on YouTube
Reply With Quote
  #9  
Old 06-18-2012, 10:39 PM
clevtool's Avatar
clevtool clevtool is offline
 
Join Date: May 2006
Location: Boone, Iowa
Posts: 343
Default

Quote:
Originally Posted by David Paule View Post
What's the difference between the substructure dies and the tank dies?

And is there any reason not to use the tank dies generally?

Why were the regular dies designed so that the rivet head would stand proud .007?

Thanks!

Dave
Substructure are .011" deeper than standard, tank are .007" deeper.

By generally do you mean everywhere? All the rivets would have spaces around (and under) them because they don't fit the dimple.

Regular dies were designed so the rivet sits flush with the surface. The proseal is what holds the rivet proud of the surface.
__________________
Mike Lauritsen
-
Cleaveland Aircraft Tool
800-368-1822
www.CleavelandTool.com
mike.toolman (at) gmail.com

Like on Facebook - Follow on Twitter - See on YouTube
Reply With Quote
  #10  
Old 06-19-2012, 08:43 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,358
Default

Quote:
Originally Posted by clevtool View Post
The dimples in this cutaway do not look as crisp as what I would expect from properly formed dimples with good quality dies.
Agree. Not enough die pressure on the bottom sheet, in this case a rib flange. But that's a distraction, an aside to the real issue.

The focus here is on the oversize dimple immediately under the rivet head, 0.007" deeper and 0.0167" wider at the major diameter. Assume it to be perfectly formed as would be the case with a Cleaveland die and a skilled operator. Let's assume the use of a substructure dimple (0.011" deeper) and perfect nesting. Further assume the rivet head neither bent or cracked, and illustrations of such are mere anomalies. As intended, the tank die would result in a space under the rivet head. The space would, in theory, be filled with sealant.

Being rubber, the sealant would be roughly 10,000 times less stiff than aluminum (10,000,000/1,000). In the context of structure the rubber contributes only a tiny bit more than nothing, or about the same as air.

So, consider this question: Having purposely left a space under the rivet head, what happens when a structural load is applied to the joint?

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 12:35 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.