Countersink out of round

RVG8tor · #1 03-03-2008, 05:54 PM

Would you use this part? I did the countersink into the 606 trim spar. I drilled a #40 hole into some MDF as a guide for the countersink bit. I guess as I went along the hole in the MDF go bigger allowing the bit to move around a bit. The photo is the worse one, all of the others are out of round a bit but no worse than the space around a dimpled hole. I think all but a few of the holes are a little out of round. The last one is bad because it allows the rivet to set too deep, I can see a bit of where the rivet shaft meet the angled rivet head.

I countersunk slightly deep of flush since the skin goes on top but when I cleco the skin to the spar I see a gap, is this normal? See photo. Thank you in advance for any advice. Click on the image to get the big version.

Underside of hole.

Gap when clecoed

bullojm1 · #2 03-03-2008, 06:19 PM

Mike-

Correct me if I am wrong, but the mugly countersunk part is sandwiched between the top skin (dimpled) and a hinge (just drilled, no dimple, no countersink). If so, then don't worry about it. The sandwiching effect will give you all the strength you will need, since the shop head of the rivet isn't formed against the poor countersunk skin. Build on!

Also, what I have found is using the countersinking cage with an air drill always leads to chatter and some runaway holes. I exclusively use an electric (or battery) drill on a very low speed. That has given me excellent results.

airguy · #3 03-03-2008, 10:05 PM

Quote:

Originally Posted by bullojm1

Also, what I have found is using the countersinking cage with an air drill always leads to chatter and some runaway holes. I exclusively use an electric (or battery) drill on a very low speed. That has given me excellent results.

I'll second that. It takes longer, and it's a pain, but it doesn't chatter.

And yes, I would use that part. For what it's worth, I did ruin and throw away a few parts using the same technique you describe, with the hole in the MDF. I subsequently quit countersinking over the table for that reason, and always countersink over free space where I don't have to worry about the tip of the countersink bit hitting anything on the other side of the hole and interfering with the cut.