Wingtip rib was previously prosealed in place, clecoed every hole.
Proseal now fully cured.
Remove every other cleco.
Machine countersink holes using permagrit countersink. After numerous test with different c-sink bits, the permagrit bit gave the most accurate and cleanest c-sink.
Rivet wingtip rib.
Remove remaining clecos and repeat.
I decided, with van's concurrence, to use CS4-4 rivets in the top aft hole, and the bottom aft two holes due to insufficient clearance for my hand and a bucking bar.