When a vehicle has been in a collision, the forces that produce dents in the car or truck stretch the thin sheet metal out of shape. This means that even if you push the dent back out, it still may not look quite right. This is particularly problematic in smaller dents, such as those approximately the size of a golf ball. In these cases, you have to use tools that will allow you to shrink the sheet metal so that you can make the panel fit correctly once again.
Heat the panel that requires shrinking using the propane torch. Take note that this is not always necessary. It makes the metal more malleable and allows the shrinking hammer to work more easily and quickly, but it can easily warp the panel if you apply too much heat. Ideally, it should be hot enough for the paint to singe off, but not be bright red or orange.
Position the dolly on the concave side of the dent. This provides the hammer a backer so that it won't bend the sheet metal too far out of position.
Strike the convex side of the dent sharply with the shrinking hammer. You will notice that the hammer has teeth on its face like small, sharp pyramids. These are what shrink the sheet metal. As you strike the metal, the teeth imprint on the steel, slightly deforming it shrinking it in the process.
