The bottom edge of the spar needs to be machine countersunk because the flap hinge mounts on the inside surface of the spar.
The top edge can be dimpled to receive the skin dimples.
Here are the flap skins, spar, and hinges, all deburred and ready for priming.
The flap ribs, brackets and shims are also all ready for deburred, dimpled/countersunk, etc. and ready for priming.
