[MP&C]

The "donut dolly" is UHMW; it is used for shrinking, so given your welding operation has already shrunk the metal, you wouldn't use it in that instance. I was removing some body damage (stretch) on the bumper filler panel and using the crowned hammer with the donut dolly, which is why you see them there...

The dolly you are using should closely match the side of the panel it is held against, without having sharp edges pressed against the metal. The hammer should follow the same principle, so given most panels have a slight crown on the outside, a flat hammer is what you'll use the majority of the time...

I wouldn't go overboard in applying pressure to the dolly. As long as you don't see a wavy panel, it isn't shrunk to the point of metal gathering. Planish each weld dot a couple times or so and move on. Once all is complete, then do a good read on the panel and see what needs to move where..