To get started, I finished dimpling the skin holes that interface with the rudder skeleton.
To countersink the trailing edge wedge, I used a drill guide I bought from Cleveland Tool. It basically just keeps the outer edge level with the ground. It actually worked pretty well.
It was pretty easy to countersink the first side of the wedge. I just used my countersink cage to hit all the holes.
Countersinking the opposite side was a bit harder because the pilot holes had already been opened up by the first countersinking op. For the the opposite side, I just clamped up the wedge and drill guide into my drill press. This kept everything locked-in. It worked out great.
After countersinking both surfaces of the wedge, I deburred the knife edge the formed at the intersection of the 2 countersinks. That’s it for the wedge drill prep.