Body metal has a "memory"- - - -it wants to go back to its original shape before the damage went in, providing the metal has not been severely creased, stretched, or torn. The body man's job is to carefully reverse the damage while creating as little further distortion as possible. The purpose of hammer and dolly work is to reverse the original bending forces in the exact opposite direction, if possible. Once metal is stretched, it needs to be heated and rapidly cooled to shrink back to its original shape. I use an acetylene torch with a very small tip and a needle-point neutral flame to heat an area about half the size of a dime red hot, then quench it with a water-soaked rag to rapidly cool the spot. Immediately after the heat/quench procedure, use a hammer and dolly to flatten out any distortion. This is one place where "hammer on dolly" work is needed, but only light to moderate blows with the hammer are used to prevent further stretching. Repeat the heat/quench/hammer sequence in several places to pull the stretched spot back into shape.
Jerry
