Brief Description: Preparing the main spar - countersink spar flange
After looking at the different methods being used for countersinking the fuel tank attach holes in the spar flanges to accept the dimples in the fuel tank skin, I decided to go with Van's technique. I think Van's idea to use the nutplate as a guide for the countersink cutter is a pretty good one and should make this job go pretty quickly.
First thing to do was countersink the nutplate fasterner holes with a #40 cutter. I then primed the bare aluminum, then installed the nutplates.