countersink knife-edge

[prkaye]

When I countersunk those holes in the wing spars for the #6 screws, in order to get deep enough for the screw head the countersunk hole becomes enlarged. I've read on previous threads people say that this is OK, and I agree, since the nutplate will do the work of holding the screw in place.

What does concern me is the resulting knife-edge of the countersunk hole. If the countersinking enlarges the hole, this means the countersink blade has cut all the way through the depth of the hole, and it must then leave the hole with a sharp edge (around the perimeter of the hole at the bottom of the countersink).

I didn't like this, so what I did was take a very small low-power hand dremel-type tool and a very small grinding attachment, and run this in the holes, smoothing out the knife-edge. Then I poked and spun a scotchbright pad in each hole to further smooth the knife-edge. Then I primed inside each hole.

This was my solution, but maybe i was worried about nothing. Has this knife-edge on countersunk holes (e.g. for screws/nutplates on wing spars) concerned anyone else? Any other solutions?

[Les Dial]

Same thing for me. We don't leave sharp edges on production aircraft in anything if possible. I used a Burraway and gently cleaned it up. It opened the ID of the hole about .004-.005" more but the trade off is worth it. the rest ofthe MRB engineers agreed as well. -- Les