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Old 09-20-2019, 09:35 AM
Desert Rat Desert Rat is offline
 
Join Date: Aug 2018
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Default question on dimpled hole tolerance

Hey all,

I bought a used kit with the empennage already finished, but the HS has a couple of issues, so I unskinned it. I then checked the substructure prior to reskinning to make sure I hadn't blown out any of the holes.

Obviously, dimpling will open up a hole slightly, but I can't find a spec anywhere. I did a couple of test coupons with new dimples and determined that for a #40 dimpled hole a 7/64 drill bit seems about right for a no-go gage but I found a few holes left over from the original builder that are exactly 7/64, i.e. it goes (barely) instead of "no-goes." I definitely didn't blow these out when I drilled the skin off, because they still have primer in them.

To cut to the chase, what is an acceptable hole size for a dimpled -3 rivet?
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  #2  
Old 09-20-2019, 01:35 PM
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JonJay JonJay is offline
 
Join Date: Jan 2007
Location: Battleground
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Quote:
Originally Posted by Desert Rat View Post
Hey all,

I bought a used kit with the empennage already finished, but the HS has a couple of issues, so I unskinned it. I then checked the substructure prior to reskinning to make sure I hadn't blown out any of the holes.

Obviously, dimpling will open up a hole slightly, but I can't find a spec anywhere. I did a couple of test coupons with new dimples and determined that for a #40 dimpled hole a 7/64 drill bit seems about right for a no-go gage but I found a few holes left over from the original builder that are exactly 7/64, i.e. it goes (barely) instead of "no-goes." I definitely didn't blow these out when I drilled the skin off, because they still have primer in them.

To cut to the chase, what is an acceptable hole size for a dimpled -3 rivet?
To my knowledge, it is the same as called out in MIL-R-47196A.
#40 = .103 max hole diameter.
So, 7/64th's would be slightly larger, by a few thousand's.
I think it makes a great no-go gauge. Personally, I would not fret about a hole here or there, only if you had more than a couple in a row, or several in a common load path.

When you set a rivet, it swells into the hole and can enlarge the hole slightly so I am not surprised that you found a few just out of tolerance.
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