Experiment: Tank dies for substructure dimpling

Preparing to dimple my wing ribs, I decided to test whether I could tell the difference when tank dies were used to dimple the substructure.

I drilled two test sheets, drilled #40, dimpled with DRDT2, and backriveted AD3-3.5. Top piece is .032" (such as inboard wing skins), bottom is .025" (main ribs).

Top test piece: standard dimple die top, tank die bottom (Cleaveland die, 0.007" deeper than flush).
Bottom test piece: standard dimple die top and bottom

In the top piece, there is no visible gap between the skins between the two rivets. In the bottom piece, there is a slight gap. Conclusion: tank dies for substructure produce tighter nesting dimples. I'll be using these for dimpling substructure.

Van's manual section 5.5 says to machine countersink 0.007" deeper than flush to accept a dimpled skin. So it would make sense that you would want to dimple the substructure 0.007" deeper as well.

EDIT: Looking at this again, I underdimpled slightly.

Sold...

Thanks for posting this high resolution pic. I've been exchanging messages with Mike Lauritsen (Cleveland Aircraft Tool) about this same topic as I was about to purchase substructure dies for my next project. I think I'll place an order!

Careful, the "substructure" dies are 0.011" deep, while the tank dies are 0.007" deep.

I think 0.011" is possibly too deep.

See http://www.vansairforce.com/community/showpost.php?p=729592&postcount=1
Using the same formula, a 0.025" skin needs a 0.008" deep dimple. A 0.032" skin needs a 0.010" deep dimple.
I think it's better for the substructure dimple to be slightly shallow than slightly too deep, to prevent the dimple in the skin from being loose. I think 0.007" below flush for 0.025 and 0.032 skins is a reasonable compromise. It also matches Van's recommendation for machine countersink depth. And also means you only need two sets of dimple dies, not three.

There's some threads on here suggesting that the substructure dies are actually too deep. Here's another experiment comparing the 3 types of dies used for substructure:
http://www.vansairforce.com/community/showpost.php?p=885006&postcount=13

I have both the tank dies and substructure dies, I think the substructure dies are to deep, I prefer the tank dies, they work great for me and still provide a nice tight fit.