R-916 countersink decision

[Lemmingman]

After much trial and error, I have come to the conclusion that my countersink cage will either make a nice countersink that sits a hair proud off the dimple but leaves the hole intact or with one more click sit flush but slightly tear out the hole on the other side leaving a more wobbly seating for the rivet.

I know others have had this before, what did you do? Which is the lesser evil in this case.

This is the trailing edge wedge for the rudder.

 

[1911pilot]

I just did this on my 9 rudder. Twice...
I ended up countersinking a few clicks more than it took to get a rivet flush. You'll end up with a slightly enlarged knife edged hole in the AEX wedge. You may have to file the dimples in the skin a bit to really get it flush.

The first time I tried it on the table edge, not fun. The second time I held it in my hand and it worked a lot better for me. FYI, the piece is $32.50.

 

[terrye]

Csk Aid

I think you are discussing a situation where the countersink starts to break through the opposite side of the material. By doing so, you lose the pilot diameter of the rivet hole and the countersink flutes chatter in the hole and result in a rippled surface to the countersink.

I resolved this by making a backup strip (in my case from a 1" x 1" x 1/16" angle, but any piece of aluminum will do), clamping it to the opposited side of the material, drill through with the rivet size drill (#30, #40) and then countersinking. The backup strip guides the countersink pilot as the flutes break through far side of the part. This is especially recommended for the fuel tank platenut holes in the wing spar.

 

[1911pilot]

One more thought. The 2nd time I used my dewalt instead of the Sioux. Slower seemed to work a lot better.

 

[flion]

On the similar wedges in the -10, I did basically what terrye suggested except that I simply drilled the wedge to the edge of a flat board, clecoing as I went, and then went back and countersunk it. I then turned it over and clecoed it back down and countersunk the other side. The holes drilled into the board acted as a pilot guide (at the right angle, too) and kept the countersink bit from walking or ovalling the holes. Drilling at the edge of the board meant that the board itself did not interfere with the countersink cage as it matched the angle of the wedge surface. Not to worry if the hole in the wedge is enlarged a bit; it will center on the skin dimples and they will center the rivets.