Frame Straightening with Heat

[Kevin in NJ]

The principle of metal that we must all accept and understand. When you heat up metal past its plastic point the metal will shrink.

At one point I read the plastic point starts where you get the metal taking the blue color. At this point the pressure from the surrounding metal cause the now more movable atoms the push into themselves. During cooling the pressure from the heat expanded metal does not go away until way after to get back to the solid point. So the shrink stays.

I believe you would want a hotter heat source then propane. A fast heat in a narrow line gives more control in my limited experience.

Frames and sheet metal are low carbon steel and will not suffer any significant effects from heating.

You do not want to quench. The metal keeps a better shape if you let it cool significantly first. I will use a wet rag to faster equalized the temp of the metal.

It is important to allow the metal to fully equalize in temp. A little heat will distort the metal and you will not get it right. I believe the number one reason why metal shrinking by heat is bad to do is because most guys are impatient. You need to be conservative and patient. You must think and plan how you are going to do the shrinks.