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  #1  
Old 09-04-2018, 07:31 AM
Beagle's Avatar
Beagle Beagle is offline
 
Join Date: Apr 2015
Location: Vienna, VA
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Default Is Drilling Tank Skins to #41 a Good Idea?

Question to the combined VAF wisdom: Is Drilling Tank Skins to #41 a Good Idea?

Rationale: I am about to start drilling my tanks and it occurred to me that when I dimple regular #40 holes they end up slightly larger. So, in the interest of having tanks that don't leak I want to minimize gaps wherever possible. After dimpling, a #41 hole should fit a AN426AD3 rivet with a little less slop. Then there will be less gap to challenge the ProSeal and less likelihood of a leaky tank.

I've read someone on VAF mention that others have done it but searching "#41" comes up with nothing.

Thanks in advance for answering!!!
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  #2  
Old 09-04-2018, 07:41 AM
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Robertc Robertc is offline
 
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Default

I used #40 every where because the rivet expands to fill the hole. You might need to adjust length of rivet, but here you go. Bob

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  #3  
Old 09-04-2018, 07:52 AM
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Default

It won't hurt anything, but not really necessary. Like Robertc says, the rivet expands slightly to fill the hole.
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  #4  
Old 09-04-2018, 08:15 AM
rocketman1988 rocketman1988 is offline
 
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Default And...

Drilling to #41 May also cause you grief when trying to install the rivet as it will be a tighter fit...
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  #5  
Old 09-04-2018, 08:35 AM
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Default

With the way the proseal is applied along the seams, the rivet itself isn't likely to be the leak point - at least not in a way that 40/41 is going to solve.

I don't see a downside to it, I just don't see much upside either.
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  #6  
Old 09-04-2018, 09:08 AM
jibby212 jibby212 is offline
 
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I always use #41 when the hole will be dimpled, after dimple the hole is still plenty big for a rivet, that's just how I do it.
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  #7  
Old 09-04-2018, 09:24 AM
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Default #41

Try reamer. If you use #41, make sure you're simple die fits. You don't want to create a stress crack.
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  #8  
Old 09-04-2018, 09:34 AM
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Default

The dimensional difference between a #41 and #40 drill bit is 2 thousandths of an inch.

That small difference has no influence on whether a riveted joint is leak free or not, but if it makes someone feel better there is nothing wrong with it as long as the pilot of the dimple die being used. fits the hole diameter. If it is stretching the hole because it doesn't fit without interference, you could be unknowingly degrading the hole.
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  #9  
Old 09-04-2018, 10:17 AM
WingsOnWheels WingsOnWheels is offline
 
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The RV-6 manual calls for #41, which is just fine and dandy until you realize you drilled the longerons with #41 and now your countersink pilot doesn't fit. Not that I would know anything about that.
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  #10  
Old 09-04-2018, 10:27 AM
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Beagle Beagle is offline
 
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Default

Thanks for the great input! I'm hearing a few key points:
-Either #40 or #41 are fine since the size difference is so small and the rivet will expand to fill the hole anyway.
-Make sure the dimple die pilot fits a #41 hole to avoid cracks.
-Also, consider using a reamer.

Thanks folks!
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