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Tight Countersink

J

jwilbur

Well Known Member
In the image, I need to countersink the 3/32 hole in the top center. This is the wing spar and the countersink is for the fuel tank attach nutplates. It's a tight spot because of the height of the step bar behind the hole. Even my modified cage (visible in the image) doesn't fit. See page 13-4 of the RV10 plans. I started to do it by twisting the csk cutter with my hand but decided I'd ask how others managed this one before doing something dumb.

2co1qbt.jpg


Thanks,
 
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tip

Remove the bit from your auto countersink tool. Install it in your 90deg air drill (same thread). Countersink your part.
Ryan
 
Speed debur

I placed mine in the speed deburring tool and did it very carefully...No need to cut the microstop in half.

Cheers
 
I used my deburring tool with extension and piloted bit. Also as above my "snake kit". You'll need to use this method in several other places.
 
Hex adapter

There is a thing called (IIRC) a "hex adapter" which has the thread for a countersink cutter or a threaded drill bit at one end and the other end fits into anything that takes a hex bit. Alternatively, the hex end can be chucked up in a cordless drill, which is what I do when countersinking in "suicide mode" as is required here. The cordless drill will give you terrific control of your speed.

This is a very handy little tool to have. I normally use it with my deburring bit, mounted in a rechargeable electric screwdriver, as my hole deburring tool of choice
 
Tap the roll pin out of the collar on the back end of the countersink that you have shown. Carefully disassemble the tool and use the shaft only out of the countersink in your drill. Feed slow and keep checking the depth.

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I used the countersink bit removed from the microstop with the threaded drill bit mount from my angle drill kit:

DCP_1332.JPG
 
While we are on the subject, I had the fuselage structure assembled and was putting the skins on when I discovered that there was no good way to reach the skin joint holes in the F-1004K-L/R parts. I ended up using an extension and hand-countersinking near the spars but this is a part that can be done before assembly. There is nothing to be done about the spar web but four holes by hand was not a hardship. You will also run into this again with the F-1015C parts where the flanges at the ends prevent access and on the flanges themselves, though I think a modified cage will work. I just did mine by hand.
 
If it is just for a nut-plate, you can also just trim a little material away by hand and use the so-called Oops rivet. Took me a while, but I eventually embraced this little beauty....... ;)
 
paul330 said:
If it is just for a nut-plate, you can also just trim a little material away by hand and use the so-called Oops rivet. Took me a while, but I eventually embraced this little beauty....... ;)
Click to expand...

Paul,
I'm not following you here. Why would you use an oops rivet, essentially a -4 rivet shank with a -3 head, in this instance? Unless you have a rivet that's different than what is normally called an oops rivet, the amount of material required to be removed for the CSK is roughly the same and I can't see drilling out the nutplates to 1/8 over 3/32. What am I missing?

I, like most of the other's, simply did them free hand. In my case with my deburring bit that's on a hex adapter chucked into a cordless screwdriver. And like FLION pointed out there's other times you are going to need to CSK where a microstop isn't going to fit.
 
Master craftsman Dave Howe in California uses the so called oops rivet in nutplates. The rivet spec is NAS1097-3-2.5 It has a 3/32" shank and a tiny head, these should only be used in pure shear applications. They take less of a countersink, and we make dimple dies that fit them as well.

Also for the discerning builder, and also commissioned by Mr. Howe we make a set of screw dies for the same thing. Shear only applications the NAS8702U2 allows for a screw that looks smaller than a #6 and has the shank of a #8. As most are aware the larger the dimple the larger diameter of stretching occurs around the hole that is being dimpled. For inspection panels this screw will minimize this stretching an give a super smooth look.

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IIRC "hex adapter"

Mike, do you guys at Cleaveland Tools sell anything like what Loman describes? I searched the web site but could not find it.

Loman said:
There is a thing called (IIRC) a "hex adapter" which has the thread for a countersink cutter or a threaded drill bit at one end and the other end fits into anything that takes a hex bit. ...
Click to expand...
 
Auburntsts said:
Paul,
I'm not following you here. Why would you use an oops rivet, essentially a -4 rivet shank with a -3 head, in this instance? Unless you have a rivet that's different than what is normally called an oops rivet, the amount of material required to be removed for the CSK is roughly the same and I can't see drilling out the nutplates to 1/8 over 3/32. What am I missing?
Click to expand...

As explained, it's a 3/32 with a small head - a mini version of the one we use when we have to drill out a hole oversize. Not that I've ever had to do that :eek:

The beauty of it is that you can avoid dimples and hence having to dimple the nutplate. Becuase of the small head, a couple of turns with a deburring tool by hand makes a big enough c/s and it can be used on skins down to about 20 thou.
 
Got it! It still amazes me that after 5 years of building I keep learning new things all the time here at VAF.
 
Auburntsts said:
Got it! It still amazes me that after 5 years of building I keep learning new things all the time here at VAF.
Click to expand...
Yes, I didn't learn until halfway through the fuselage. All the nutplates on my next plane with be held with 3/32 NAS rivets. I now can't imagine why one would want to dimple or countersink and suspect that Van's doesn't just send these standard b/c then they'd have to change all their drawings to show different callouts.
 
Good information!

This is good to know, so that when I get to this point, I'll have an idea of ways to complete the countersink. I have a 90 deg drill, so the only question is which technique to use!?:eek:
 
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