Just for reference, Dimple countersinking the piano hinge material gently using a hand squeeze does not distort the material and ruin the hinge. I did this to all my piano hinges with the pin installed in the 2 hinge halves on the bench. You get a gentle curve over the length of hinge piece, but nothing that causes a problem. You can simply straighten it out and cleco it back into position for riveting.
If you tried to the same with a pneumatic squeezer set to close too tightly, I suspect it may cause an issue.
On my flaps, the skin, spar, and hinge are all dimpled and riveted together with no problem whatsoever.
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