F772 dimple or countersink

[JurgenRoeland]

I came to the point of dismantling and finishing the forward fuselage on my RV7.

I am wondering if you dimple or countersink the F-772 forward bottom skin.

In theory, I assume you "could" countersink the bottom skin as it's 0.040 in gauge. This seems to be a case where you have a choice (as the section 5 states: we recommend dimpling in metal 0.040 and thinner)

I am more into dimpling the bottom skin and countersinking the F772B floor stiffeners.
The countersinks on the floor stiffeners will - in that case - probably have to be a bit deeper since the dimples in the bottom skin will be thicker due to the bigger gauge skin.

any thoughts ?

[Mel]

I always recommend dimpling over countersinking if you have a choice.

[Marc Bourget]

Deeper countersinks, yes!

The minimum criteria is the inability to slip a .002" feeler gauge between the mating surfaces of the skin and the stiffener.

Make sure you fully form ("coin") the dimples.

[drone_pilot]

I dimpled mine. While riveting a few places I didn't like how the rivet seated so I touched the dimples very slightly with a countersink. I'll let you know if she falls apart. :0)

[JurgenRoeland]

Thanks for the replies. I went on with countersinking the floor stiffeners and made a sample .040 sheet with some clean dimples. They are deep enough now and fit well but I'm still worried about the "the inability to slip a .002" feeler gauge between the mating surfaces".
I use a primer from akzo nobel and that usually also adds some thickness and change of shape. On the other hand I'm afraid to go too deep now so I'll move on and prime like this and check again once all parts are primed for a good and snug fit.