Finished the machine countersinking on the wing spar. I used an alodine pen to treat the countersink holes. I only did one side of each spar, since I wanted to let the alodine dry before flipping the spar and doing the other side. The nice thing about this alodine pen is that it doesn't have to be rinsed afterwards to neutralized the chemical process. You just let it dry.
I still have to countersink the fuel tank mounting holes as well as the inspection plate holes. I sure will be glad when I'm doing with drilling all the holes on the wing spar. I estimate there are about 1,200 holes on these spars. The work isn't difficult, just very tedious.