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  #1  
Old 11-13-2012, 06:49 PM
fred gassit fred gassit is offline
 
Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
Default Repair advice needed for #8 dimple cracks

Gday All

I have been careful (and lucky) until now in avoiding cracks in these #8 screw dimples but I have got some now in one of my F-820 fuse skins where it attaches to the gear weldment.

I am wondering what repair options are available, the cracks are not overly long but some are deep and can be seen from both sides.

Any repairs may need to incorporate the countersunk reinforcement plate and 4130 plate underneath.

Any and all advice is welcome!

Thanks in advance.


Last edited by fred gassit : 11-13-2012 at 07:18 PM.
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  #2  
Old 11-14-2012, 05:18 PM
g zero g zero is offline
 
Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
Default Cracks

How did you form the dimples , squeezer , DRDT or C frame ? I have only used a pneumatic sqeezer and the DRDT to form dimples , but I noticed the fuel tank instruction spell out to use the C frame and hammer to form the dimples . I have not seen any cracks in the dimples , but have not used the C frame .
Tom
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  #3  
Old 11-14-2012, 05:27 PM
DaAV8R DaAV8R is offline
 
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Location: Lee's Summit, MO
Posts: 747
Default

Quote:
Originally Posted by g zero View Post
How did you form the dimples , squeezer , DRDT or C frame ? I have only used a pneumatic sqeezer and the DRDT to form dimples , but I noticed the fuel tank instruction spell out to use the C frame and hammer to form the dimples . I have not seen any cracks in the dimples , but have not used the C frame .
Tom
Have you dimpled the tank skins for the #8 screws?
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Robert Williams
Lee's Summit, MO
RV-8 - Empennage & Wings Done
Working on Fuse
O-360-A1A

1946 Cessna 120
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  #4  
Old 11-14-2012, 06:25 PM
g zero g zero is offline
 
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Location: palm coast fl.
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Default Dimples

Not yet .What ya thinking ?
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  #5  
Old 11-14-2012, 07:48 PM
DaAV8R DaAV8R is offline
 
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Location: Lee's Summit, MO
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Default 8 dimples

Quote:
Originally Posted by g zero View Post
Not yet .What ya thinking ?
Drill and dimple a test patch using the dies and technique which will be used on the tank skins. I did this and found most if not all the dimples were cracked. I increased the hole size one numbered drill bit at a time until I didn't see any cracks.

Like most others, I am using good quality crisp dies. I have a suspicion that a cheap set of dies might not cause as much cracking but I haven't done any testing.

I probably wouldn't be overly worried if I had a crack in the tank skin but I wouldn't be real excited to have a known crack in the 820 skin. I would probably replace the skin.
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Lee's Summit, MO
RV-8 - Empennage & Wings Done
Working on Fuse
O-360-A1A

1946 Cessna 120
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  #6  
Old 11-14-2012, 09:19 PM
fehdxl fehdxl is offline
 
Join Date: Mar 2005
Location: Bellevue, NE
Posts: 686
Default

While it won't help with the current situation, this thread may help avoid the issue in the future. http://www.vansairforce.com/communit...ad.php?t=68593

Pasted from the thread above is something I noted a while back.
Quote:
Also, please note that you really want to make sure those #8 and and #10 screw holes are smooth and de-burred well before dimpling. Don't over-do it...but just get it right. There's a lot of bending and stretching going on and the chances for cracks around the dimple edge is higher than the smaller holes.
-Jim
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  #7  
Old 11-14-2012, 11:11 PM
fred gassit fred gassit is offline
 
Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
Default

I think in my case I've been more lucky than good until now. My fuel tanks worked out ok as did one of the F-820 skins.

I used a hand squeezer on the skin, not sure of my thinking now, probably along the lines of being able to control the rate of distortion.

I've been aware of the propensity for cracking and been careful but the one thing I haven't done is use a larger pilot hole.

It is possible my hand squeezer causes cracks more often but it is also used more in those awkward, heavier gauge situations where they are more likely to occur

If I replace that skin (looking likely) I'll certainly be following what has been suggested here and on other threads and opening the holes up a little more.
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  #8  
Old 11-15-2012, 11:35 AM
DaAV8R DaAV8R is offline
 
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Location: Lee's Summit, MO
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Default New skin

Fred,

I see shipping might be an issue for you. If you have access to material use the old skin as a pattern and make a new one. Common technique in the world of restoration.
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Robert Williams
Lee's Summit, MO
RV-8 - Empennage & Wings Done
Working on Fuse
O-360-A1A

1946 Cessna 120
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  #9  
Old 11-16-2012, 02:00 PM
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clevtool clevtool is offline
 
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Location: Boone, Iowa
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Default

Reaming the hole rather than drilling may help as well.
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  #10  
Old 11-19-2012, 12:50 AM
fred gassit fred gassit is offline
 
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Location: Perth western Australia
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I'll be doing that as well thanks, just before I get one of your die sets for #8 screws.
Incidentally, do you have an opinion on using a larger pilot hole than specified for those holes?
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