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11-13-2012, 06:49 PM
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Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
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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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11-14-2012, 05:18 PM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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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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11-14-2012, 05:27 PM
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Join Date: Jul 2009
Location: Lee's Summit, MO
Posts: 747
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Quote:
Originally Posted by g zero
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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Have you dimpled the tank skins for the #8 screws?
__________________
Robert Williams
Lee's Summit, MO
RV-8 - Empennage & Wings Done
Working on Fuse
O-360-A1A
1946 Cessna 120
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11-14-2012, 06:25 PM
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Join Date: Jun 2007
Location: palm coast fl.
Posts: 945
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Dimples
Not yet .What ya thinking ?
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11-14-2012, 07:48 PM
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Join Date: Jul 2009
Location: Lee's Summit, MO
Posts: 747
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8 dimples
Quote:
Originally Posted by g zero
Not yet .What ya thinking ?
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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.
__________________
Robert Williams
Lee's Summit, MO
RV-8 - Empennage & Wings Done
Working on Fuse
O-360-A1A
1946 Cessna 120
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11-14-2012, 09:19 PM
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Join Date: Mar 2005
Location: Bellevue, NE
Posts: 686
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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:
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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.
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-Jim
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11-14-2012, 11:11 PM
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Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
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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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11-15-2012, 11:35 AM
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Join Date: Jul 2009
Location: Lee's Summit, MO
Posts: 747
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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.
__________________
Robert Williams
Lee's Summit, MO
RV-8 - Empennage & Wings Done
Working on Fuse
O-360-A1A
1946 Cessna 120
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11-16-2012, 02:00 PM
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Join Date: May 2006
Location: Boone, Iowa
Posts: 342
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Reaming the hole rather than drilling may help as well.
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11-19-2012, 12:50 AM
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Join Date: Nov 2008
Location: Perth western Australia
Posts: 26
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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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