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wing spar countersinking

S

Steve

Well Known Member
The large diameter on the bottom of the #8 dimple tangent to the flat on the .032 test piece measures about .40 dia. Therefore I need a .40 dia at the top of the countersink on the spar to enable contact between the spar and tank surfaces. My #30 pilot c'sink has a .375 outside dia. Needless to say, there is a small gap between the spar and the test piece (and tank skins later) caused by the radius of the dimple touching the top corner of the c'sink.
Q. Do I need a larger dia. countersink bit?
Q. Use a different brand dimple die (I use Cleaveland)?
Q. Press on and ignore the .025-ish gap?
Q. Will tightening the #8 tank skin screws close the gap?

Many Qs for the group,
Steve
 
Steve said:
The large diameter on the bottom of the #8 dimple tangent to the flat on the .032 test piece measures about .40 dia. Therefore I need a .40 dia at the top of the countersink on the spar to enable contact between the spar and tank surfaces. My #30 pilot c'sink has a .375 outside dia. Needless to say, there is a small gap between the spar and the test piece (and tank skins later) caused by the radius of the dimple touching the top corner of the c'sink.
Q. Do I need a larger dia. countersink bit?
Q. Use a different brand dimple die (I use Cleaveland)?
Q. Press on and ignore the .025-ish gap?
Q. Will tightening the #8 tank skin screws close the gap?

Many Qs for the group,
Steve[I had the same problem. You can use a hand crank counter sink/deburring tool a few turns on each hole to seat the skin. You don?t want to go too deep or you'll start to pull the skin down and you'll get some puckering between the screws (been there done that). If you get the skin down and your screw heads are sticking up a little bit you can also give the dimple on the skin a couple of turns with the deburring tool to set the screw in a little deeper. All in all you?re probably okay structurally the way you are right now. Anything else is just builder finesse. The touque on a # 8 screw is not much.
RP]
Click to expand...
 
I measured my female #8 dimple die at 0.36" and found that if I countersink to that size or a tiny bit less, the skin sits flush when the screw is tightened. All #8 dimple dies should be of pretty similar size, one would hope!

Regards,
Conor
#90990 wings
 
C'sink bits

Thanks for the info,
The O.D. of the Cleaveland bit is .375. Brown Aviation's bits are .500 dia. I'll order a bit from Brown later today. Maybe another micro-stop cage, too. Can't have too many.

Steve
90979
 
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