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How to countersink these holes?

ravenstar

Well Known Member
Well, I promised lots of questions a few months back and my first RV-12 kit finally arrived and it hasn't taken long for me to run into my first puzzle: I can't figure out how to do countersink a hole in tight quarters. On page 06-04, step 3 the instructions innocently say to countersink four holes, but two of the holes are next to a flange and my 1" diameter countersink cage doesn't come close to fitting. I don't see any narrower cages online, and I haven't found anyone else mentioning this problem. So how did you all manage to accomplish this step? I've attached the plan diagram and a photo of the actual part. The holes in question are 1/4" away from the flange.

Am I missing something obvious?

Thanks!
 

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I knew it was something obvious. (What do you mean a tool can be used for two different purposes?)

Thank you all!
 
If I remember correctly, I did this step by hand using this speed deburring tool.

https://www.aircraftspruce.com/catalog/topages/speeddeb.php

Instead of using the hole deburring bit that comes with the tool, I used the same countersink cutter that I normally use with a countersink cage. It takes about a minute to countersink each hole, and you can stop turning the handle for a few seconds to check your progress. Practice on some scrap to get the hang of it, but it’s really pretty easy.
 
If I remember correctly, I did this step by hand using this speed deburring tool.... Practice on some scrap to get the hang of it, but it’s really pretty easy.

I have a similar tool so I popped in the countersink bit and drilled those holes in no time. Thanks! I think I prefer the hand countersinking for the control it gives me. I feel silly for not thinking of this myself.
 
I think most people would drill this countersink by hand in some way without a microstop countersink. However, just to put out all the options there are microstop cages available that don't have the full 360 degrees enclosed. There are a few different configurations. The one I'm thinking about only has half a cage so it might work in your situation. BTW I don't have one of these.
 
I can’t remember this part. It’s been almost 9 years since I finished my build, but here’s a stupid question: which way is the angle pointing, toward or away from the viewer? Isometric drawings can be confusing. Check the context in which the part is to be used to be sure ou have the correct side to countersink.
 
with an adapter, countersink bit in a drill press (no cage). the drill press has it’s own depth stop mechanism. a little fiddling with depth using scrap, but worked well for me.
 
I can’t remember this part. It’s been almost 9 years since I finished my build, but here’s a stupid question: which way is the angle pointing, toward or away from the viewer? Isometric drawings can be confusing. Check the context in which the part is to be used to be sure ou have the correct side to countersink.

Not at all a dumb question. I can stare at the rib drawings and watch them alternate between pointing into and out of the page like some of the optical illusions in my old college psychology texts.

In this case, the sides are bent towards us, and this piece nests inside another angle. I used the countersink bit in the hand deburring tool to make the countersink, and it worked great! I've since used it to clean up a couple of machine countersinked holes that were off by a couple thousandths.

Now, getting the rivets to stay put while I squeezed them, that's another story. Let's just say I got lots of experience drilling out rivets between this and the nut plates on the vertical stabilizer rear spar. To digress, however, it's really refreshing doing a project with no deadlines in which taking time to fix problems doesn't put you behind a schedule.
 
Now, getting the rivets to stay put while I squeezed them, that's another story. Let's just say I got lots of experience drilling out rivets between this and the nut plates on the vertical stabilizer rear spar. To digress, however, it's really refreshing doing a project with no deadlines in which taking time to fix problems doesn't put you behind a schedule.

Take a small piece of sheet cork (maybe 1/8" thickness) and place on shop-side of rivet. As you start to squeeze the cork will draw up the assembly before the rivet starts to deform. The cork will split and move out of the way to allow final compression.
 
It maybe goes without saying but when countersinking without a cage or drill stop, be careful to not countersink too deep. Even when doing it by hand, a very sharp bit can suddenly dig a countersink deeper than you expect. Ask me how I know.
 
Here’s some heresy sure to draw some abuse for me:

If you can’t get a countersink bit in there try a drill bit with a ver light touch
 
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