Scarf, scarf, scarf—and more scarf. Worked on the right wing skin scarf joint. After filing, sanding out file marks, sanding with 400 grit on both inboard and out board skins, I clecoed on the skin to check the fit. Uggg—not enough! Took the skin off and started the process all over again. Second fitting—still not enough. Removed the skin, filed some more and cleaned it up, still need to hit the inboard skin one more time—hopefully third time is a charm. Maybe I should have proceeded more aggressively, but it sure is hard to stick aluminum filings back on if too much gets cut off.