I match drilled the tank to the outer leading edge using a #30 pilot. There is a strip of aluminum between the tank (left side of pic) and leading edge (Right side of pic) that connects the two together. Eventually these holes get widened to a #19 to accept the tank attach screws. The tank rests perfectly on the Z-Brackets and with clecos through the spar into the nutplates, it holds the assembly down tight. With the tank snug up against the leading edge and the aluminum strip underneath, I used the pre-punched holes as a guide and drilled away. The copper color clecos in the photo are in the holes drilled by this step.
If you remember a few posts ago I talked about Dan Checkoway's method for drilling the Z-Brackets. Here is where it comes into play. I drilled and cleco'd the root end rib to the Z-Bracket. Using a #30 drill. Using Cleco's in every hole ensures no movement as I move to the next step. The outer holes first to center the tank, since they are prepunched.
With the tank secured to the root Z bracket and spar, I then removed the leading edge which exposes the outward most Z-Bracket for drilling. The leading edge will be deburred, dimpled, primed and riveted before it goes on the wing again. A cleco in every hole on the outer Z Bracket secures the baffle, then the tank skin and inner ribs can be removed exposing the baffle perfectly located for using the prepunched holes to drill all the remaining Z Brackets. Use a drill stop here to protect the spar.
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