Any time you strike hammer on dolly you will stretch the metal which will then need to be shrunk. What's holding the dent in place are primarily the "rolled buckles" at the top & bottom. The buckles fwd & aft are contributing but not as much. To remove the dent you need to apply outward force to the metal while lightly striking off dolly on the top & bottom rolled buckles. A body spoon will assist in spreading the hammer force over a wider area, minimizing collateral hammer strike damage. While you can "pound it out" with a hammer and/or dolly, I'll go against the grain here and recommend using a porta power if you have one. It's a great tool to apply the outward force a bit at a time while you off dolly hammer the buckles to relieve them. Just pounding it out will usually cause more damage than it fixes. You'll notice as you lightly strike the buckles, with the porta power holding pressure against the dent, that the porta power's push will lighten with each hammer strike. You'll need to hammer a little then put more pressure on the porta power then hammer more then more pressure etc.. Depending on the severity of the rolled buckles, application of heat may help.
What's happened is the metal has become work hardened and wants to stay in that position. It can be hammered straight but will have stresses in the metal that will make it weaker and prone to cracking. Remember what happens when you bend a piece of metal back and forth enough for it to break. That's work hardening that gets worse with each bend until the metal is brittle enough to part.
Once you get the overall profile close you can do away with the porta power and finish it with hammer & dolly. Try to finish it off by pushing out on the low spots from inside using the dolly while lightly striking the high spots surrounding the low area with your hammer. Hard strikes are rarely beneficial. The first day in class so many years ago when I went to body & fender trade school was to mentally picture how the dent was created. What force from which direction caused the damage. The correct repair is to do the exact opposite. Good luck.
Last edited by Tiny; 11/30/2015 5:43 PM.
