After drilling the hinges and deburring everything, I proceeded to machine counter sink all the holes on the doubler. With the firewall clamped down to the work bench it went better than expected. I deburred the hinges and then clecoed them back in place to add extra thickness to the holes when doing the counter sink operation. I just removed a cleco and counter sunk the hole then moved the next cleco over to the hole I just counter sunk and worked my way around. I had to make some small adjustments on the depth to account for the curved sections vs. the flatter sections. The curved sections wanted to go a littler deeper at the same setting for the flat sections. It turned out well.
