Proper tank skin alignment to baffle.

RV14: Page 18-03, NOTE preceding Step 7.

"To ensure proper part alignment upon reassembly, leave every tenth hole on the T-00001 Fuel Tank Skins un-countersunk." . . . . then to go back and countersink these and rivet after initial batch of sealant has cured.

How does not countersinking every tenth skin hole now help to ensure proper alignment of parts later if only 1 in 10 holes is not countersunk/riveted? Of 74'ish rivet holes, how can leaving out 7 rivets ( and the countersinking?) ensure proper alignment of those parts? I am assuming the parts referred to are the tank skins and the tank baffle. And, not countersinking can't have anything to do with alignment of the two parts, or can it?

I am definitely missing something here and I don't want to miss some bigger picture behind the instruction. Curious mind needs to know.

Countersinks

I'm taking a shot.
Countersinking the skin can result in a hole slightly larger. Leaving a few allows those holes to keep alignment.

wirejock said:

I'm taking a shot.
Countersinking the skin can result in a hole slightly larger. Leaving a few allows those holes to keep alignment.

Click to expand...

Pretty close.....

Even if the hole doesn't get enlarged, it leaves a hole with a very thin / fragile edge that can not be relied upon for good alignment.
Basically, a cleco will align the parts better and with less risk of damage to any countersunk holes if the holes in both parts are full thickness.

Now I have a question. If effort was taken to put it in the manual, isn't it reasonable to assume that it might have some value in helping you get the best result possible; even if it makes no sense to you?

Keeping parts aligned

wirejock said:

I'm taking a shot.
Countersinking the skin can result in a hole slightly larger. Leaving a few allows those holes to keep alignment.

Click to expand...

That sounds like the reason: having about 10% of the holes not countersunk and keeping clecos in those holes helps to keep the proper position of the parts while riveting the rest and to then go back and countersink and rivet those holes later.

Right arm, thanks.

rv_2002: I did assume that it may have some value. Assuming that not everyone sees the logic of every instruction in printed matter and that everybody is somebody different seeing things differently based on their life experiences . . . especially given the breadth and depth of aircraft kit instructions that on rare occasions does contain a questionable item; I'm more comfortable and learn something asking 'why' when I want to know why. Team work horses are more comfortable when they have blinders on.