[rotorwrench]

There are still a lot of folks that don't use anything but steel. My first experience with hammer welding was watching an old guy weld up holes in a model A body. He would grind around on the rust holes till he got the thickness back to a weldable range then fabricate a piece of steel to fit the hole by tracing. He made them fit tight and used magnets to hold them. He had an oxy/acetylene aircraft torch with small tips and used it to weld the holes shut working a small spot at a time and letting things cool a bit in between using the dolly to tap the weld joints a bit as he progressed. The fit was tight enough that he rarely used any filler at all. Some warpage can happen in flat panels so the art of shrinking comes into play to relieve that. The hammer and dolly work is usually done to take the shrink out that happens with the welding and help level a weld that has a bit of crown. When you don't use filler, the crowning effect is minimized.

When you do it this way, you can use spot putty to fill the imperfections after filing & grinding.