Wing spar countersinks

Joew · Post by **Joew** » Tue Dec 07, 2010 8:57 pm

After waiting a year and a half, I ordered and finally received my wing kit. I was countersinking the fuel tank attach holes (not the nut plates) for the #8 screws, using Vans method.

Two of them so far (out of thirty) are too deep and looked boogered up. I'm guessing there is nothing I can do about it, right? Considering it's the nut plate and the skin that will take the loads.

I think I have a technique down now (I was using a cordless drill also).

Did this kind of thing happen to others? If so, what did you do?

Thanks,

Joe

cjensen · Post by **cjensen** » Tue Dec 07, 2010 10:27 pm

I had a few that chattered too Joe. All I did was use a manual countersink tool on them to smooth them out a bit. No worries, move on!

Joew · Post by **Joew** » Wed Dec 08, 2010 5:02 am

I even think they are too deep to dress out with the countersink bit.

I'll keep pressing forward

cjensen · Post by **cjensen** » Wed Dec 08, 2010 8:08 am

Sounds good...if you have pics you can post, we may be able to offer more thorough solutions, but in this case, it sounds like you just had a little chattering, and as long as there are no sharp edges or cracks at the base of the countersink, moving on is the thing to do!

Post by **Spike** » Wed Dec 08, 2010 10:04 am

Here is a thread on countersinking that came about when I sliced up some parts. Some of the pictures are gone because we have since switched servers but the content should help.

For me the biggest asset in countersinking is making sure the hole is backed by something so the countersink does not slide, and not being afraid of it. Make sure the cage is sitting flush, and dont be afraid to put pressure on it at speed. Let the cage do the work of preventing too deep a csink.

Spike

Mike Balzer · Post by **Mike Balzer** » Mon Dec 13, 2010 10:06 pm

Joe,
When counter-sinking the spar, you must have a piece of metal as a back up for the pilot of the countersink to keep as a guide.

Without the extra piece of extrusion aluminum alloy clamped to the lower spar cap. .050 to .125 thickness would work just fine.

What happens is the countersink goes so deep to make the dimple fit that the pilot of the countersink does not have the metal of the hole diameter to keep the countersink running true and it begins to CHATTER.

Also your countersinks might not be too deep because you still need the metal of the dimple to fit into the countersink that is made wich is usally .005 to .010 deeper than the rivet or bolt would be if you put it in the countersunk hole.

Hope this helps,
Mike Balzer