With the fuel tank attachment nutplates riveted, I could now start countersinking their screwholes. I made a sample coupon on 0.030" scrap material with a dimpled #8 screw hole, and also the maximum inner/outer hole sizes to simplify checking if I had countersunk far enough yet. Once I had gotten the countersink cage depth set properly, the rest of the holes went along pretty quickly. A surprising amount of aluminum chips were produced, due to the size and number of these holes, but they all seem to be correct. What's next? I'll need to make another sample coupon for the inspection panel holes since those are a smaller screw size, and then countersink those holes too.