Post #7 in this thread discusses it....
55-Wagon-Progress Basically using a 3" x 1/16 cutoff wheel, perpendicular to the weld, and move it back and forth to act as a grinder. The minimal contact patch will keep any post-welding heat buildup down to a minimum, and unlike flap discs or other large grinding devices, you have a better, less obstructed view of what you are doing. So less chance of thinning out the panel alongside the weld. Grind the weld as flat as possible, keeping it just above panel surface to allow for planishing. I then use an 80 grit roloc to sand? the remainder flush with the panel.
As far as planishing, some will prefer to weld the complete pass ( dot welds) before grinding or planishing, others will weld dots in skipped intervals, grind and planish, then repeat. I would say it this weld is in the vicinity of a panel crease, that crease will tend to hold the panel shape and the grinding and planishing afterward is an option. With welding through the center of a low crown panel (ie door skin) grinding and planishing after each weld dot is recommended as a low crown panel is quick to lose shape from shrinking, and the planishing will help to keep that in check..
