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  #1  
Old 11-16-2014, 06:01 PM
aarvig's Avatar
aarvig aarvig is offline
 
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Default Drill bits gone wild...

Hey guys, I sent this to Vans but I thought I would put it out there to get the general opinion on this.
Tonight while drilling the #19 screw holes in the fuel tank skin for the dimpled holes that go into the wing spars I had a drill bit go wild on me and cause this nasty hole. The hole will be dimpled but its definitely bigger and more oddly shaped then it should be. What should I do?



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  #2  
Old 11-16-2014, 06:23 PM
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RV7A Flyer RV7A Flyer is offline
 
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Default

Deburr it, dimple it, and move on. 1 slightly larger screw hold amongst the gazillion on the tanks won't matter.

Just don't let it happen again.
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  #3  
Old 11-16-2014, 06:46 PM
Steve Steve is offline
 
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Default

Triangle holes are a common problem when drilling sheet metal. Helpful hints:
1. support the workpiece
2. use stub length drill bits

OR
1. spot drill
2. drill an undersize hole
3. ream to final size
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  #4  
Old 11-16-2014, 06:50 PM
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wirejock wirejock is offline
 
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Default Reamer

Quote:
Originally Posted by Steve View Post
Triangle holes are a common problem when drilling sheet metal. Helpful hints:
1. support the workpiece
2. use stub length drill bits

OR
1. spot drill
2. drill an undersize hole
3. ream to final size
+1
Drill under size the reamer to size. It adds a little time, but holes are exactly right.
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  #5  
Old 11-16-2014, 07:14 PM
David Paule David Paule is offline
 
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Also, it's worth getting a scale that reads in 1/100 inch. The Starrett C305R, various lengths, is ideal.

Dave
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  #6  
Old 11-16-2014, 07:37 PM
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claycookiemonster claycookiemonster is offline
 
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Default Or maybe just slow down?

Sometimes the speed of an air drill is too much. You might try drilling with a regular old rechargable drill; it's a bit easier to manage.
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  #7  
Old 11-16-2014, 07:59 PM
aerhed aerhed is offline
 
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It certainly won't hurt to drill to a 15 then dimple. Its hard to get full depth dimples for a #8 without cracking anyway.
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  #8  
Old 11-16-2014, 08:50 PM
DaAV8R DaAV8R is offline
 
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Default Cracks

I would test some material of the same thickness with your #8 dies before dimpling your tank skins. I had to increase these hole sizes a bit to prevent cracking.
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  #9  
Old 11-17-2014, 04:56 PM
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Default Drill undersize

Most of my holes were drilled undersize and then reamed to final.....they just finish out so round
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  #10  
Old 11-18-2014, 05:55 PM
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aarvig aarvig is offline
 
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Thanks for all the advice guys. The big question is, should I replace the skin? Obviously, this is something that needs to be smoothed out to prevent cracking but then it may be to big to use reliably. The other issue is that the number 19 holes that turned out perfect are almost to tight to fit a dimple die into and I'm worried about tearing the metal when I dimple these.
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