[Curt Campbell]

I agree with not overheating...no need to. The old rule of thumb I have been told is if your wet rag sizzles just a little bit it was heated enough. I do use a torch or disk on thicker metal such as on an A. The shrinking is most useful after any metal bumping or straightening has been done...or to repair oil canning effect. I have a very small heating tip for the torch.

Shrinking is only one several methods to straighten metal....and only if stretching has occurred.

Best rule of thumb is be careful not to overheat! Heck, the modern rice burners I rebuild start warping if I even push the oxygen\acetalyn torch cart past them!!!!