CSK wing skins: Am I reading this right?

Working on the top wing skins for my RV-10. Page 16.2, step #3 of the plans says to machine countersink some #19 holes and many #40 holes for flush screws/rivets. Am I reading this right? The skin is 0.032" thick and my understanding was that machine countersinking aluminum sheet this thin is generally frowned upon as discussed and explained in the following thread:

http://www.vansairforce.com/community/showthread.php?t=11409

1... Am I reading the plans correctly? If not, what am I missing?
2... Is there a better way to deal with this step (assuming I'm reading it right?)

Yes you are reading it correctly, you machine countersink the holes that are in common with the doublers on the wing walk area.

Some machine countersinking with overlapping skins too...

Indeed, it's correct and I had to think about it at that point too. But as others stated, since there is a doubler skin underneath, the countersinking is ok as there is additional material for the fastener to hold onto.

While mine is a 7 and not a 10, frequently construction is similar across vans designs.

Since you are not quickbuild, you have the option of dimpling ribs, doubler and skin. I did so on my 7 with no issue. If you decide to do so, pay attention to the holes allocated on the plans for the wing to fuselage gap fairing at the root rib. I did not dimple them.

When you do this step, pay careful attention to only countersink where the doublers are. Do not countersink the row of rivets along the spars or j-stiffener. Also, pay attention to the nutplate just aft of the j-stiffener. It's different. You have three pre-drilled holes and you drill the hole closest to the stiffener for the screw, not the middle of the three.

Thanks all -- and another question.

I went ahead and followed the plans rather than dimple. ... Thanks, Patrick, for the extra warning about the J-Stiffener and nutplate pattern. I had no issues but wondered if maybe I should have dimpled for the #8 flush screws instead of CSK - cuts through the upper skin and into the wing-walk doublers. But I suppose there's a difference between fastening with screws and fastening with rivets.

I've read about "smoking rivets" and "knife edges" in machine countersunk holes when the aluminum is too thin. Would someone be willing to give a brief explanation of why this isn't an issue for the #8 flush screws (presumably). Different material maybe? Or maybe not as "tight" a fit as a rivet? And one other thing I'm not clear on is how one finds a "smoking rivet." Do you actually see it "smoke" during a post-flight inspection?

As always, I appreciate the assistance and comments from everybody,

Do you actually see it "smoke" during a post-flight inspection?

Click to expand...

Only if it just had sex!
Seriously, a smoking rivet doesn't "smoke". You will find small dark streaks trailing off the rivet head. Its aluminum powder from the fretting action. Often feels a little greasy on the fingertip. The streaks tell you there is some movement going on.

Yes, the smoking rivet takes a while to show up. It looks like exhaust streaks except it originates at a rivet. It's pretty easy to tell the difference between a fuel stain, oil stain, and 'smoking rivet' stain.

As for the knife edge at the nutplates, not to worry. The final skin (at the root, that would be the fairing strip) will be dimpled. Likewise, the knife edges you made on the spar by countersinking will be overlaid by the tank skin and inspection plates, which will also be dimpled. The head of the screw will bear on the dimpled skin and be firmly captured laterally by the nutplate itself. There should be no fretting at the screw. When countersinking over nutplates, make a test dimple from scrap of the same thickness as the material that will go over the nutplate. You need to countersink deep enough that the dimple rests in the depression, which is a little deeper than just countersinking for the head of a screw.

Below is a picture from my KitLog site showing my test dimple in use (that one is for the #40 rivet locations):