Tonight I finished countersinking the longerons. Another round of very consistent holes. One more thing I found useful was a countersink drilling table another builder had made by measuring the thickness of the skin to be mated, he came up with a range of hole sizes. This is easier to measure than the depth of a rivet in the countersunk hole.
![](https://i0.wp.com/mytwings.com/wp-content/uploads/2020/04/img_5164.jpg?resize=648%2C449&ssl=1)