This afternoon I spent about an hour working on repairing the front apron, which had evidence of collision damage and a previous repair. I previously welded up the holes that had been used to straighten the dents before filler (but had never been filled). So the first step was to grind down those welds as flush as possible. I used my angle grinder with three metal cut-off wheels stacked up to widen the profile. This makes it easier to cut using the edge of the wheels.
After I was finished they welds where fairly flush. I used my body hammer to straighten the apron a bit by tapping the inside and holding my dolly on the face of the apron.
Nevertheless the metal was fairly wrinkled after I tried to knock the dents outward, even proud of where they should be.
So I used my shrinking disk to try to shink the metal which had first been stretched inward when the dents occurred, then stretched outward when the previous owner pulled the dents and finally when I tapped them outward with my hammer. I applied the 9″ shrinking disk, mounted in my large grinder to the surface of the apron to build up friction and heat localized to the high spots, then quenched the area using water to shrink those same spots. I repeated this many times and began to see some progress.
After spending several minutes heating and quenching I saw some progress but realized I would still need some filler to get the apron smooth again. So I cleaned the area using a 3M Clean N Strip wheel mounted in my drill.
Next I painted on a coat of the tinning compound that helps the lead-free body solder bond to the steel. I used my propane torch to heat the tin until it bubbled brown.
Once the tin turned bright silver I used a clean cloth to wipe away the brown impurities.
With the tin applied I quickly cleaned it using some hot water and once it dried I wiped again with acetone. Then I applied the solder to the apron.
After applying enough solder to stand proud of the apron I used my cut-off wheel again with the same three-disk set-up to start grinding away the surplus solder.
After grinding for about fifteen minutes to get the basic shape I switched over to my random orbital sander with a 60-grit sanding disk. One of the nice aspects of the lead-free solder is it is safe to sand, unlike lead.
The sanding blended the solder into the surrounding steel and made it much smoother. Clearly it still is not perfect, but structurally the area was set and would only require a thin coat of filler to be smooth.