Enjoy...... [ame=http://vimeo.com/24906676]HBTV: Depth of Speed - Salt Flats Speed Shop on Vimeo[/ame]
I'm curious - Why quench in the drinking fountain? Wouldn't that lead to an uneven temper, or is that the point? Does it make the metal easier to shape?
He was annealing the metal, and in the video, the metal was probably aluminum. When you work the metal, you are stretching the molecules (work hardening) which causes the material to harden and become brittle. The heating allows the stresses to neutralize and softens the aluminum back to the original state so you can continue to shape the metal. If you don't do this, the metal will crack fairly easily. In the case of aluminum, he started out using an oxyacetylene torch at a low temperature carbon rich setting (notice all the soot on the floor), then he switched over to a higher temperature as he was burning off the black soot. This also lets him see that he hasn't missed any spots during the heating. The cold water just helps to set the molecules better in the relaxed state. He had to go through several of these annealing steps before he was finished. You can tell pretty easily when it starts to harden. the pars starts out soft and flexible and then gradually gets stiffer. The metal will give off a duller sound when soft when working and then start to sound tinnier and more metallic as it hardens. He was using a pneumatic hammer, and he had a steel "teardrop" plate template he sandwiched against a lead shot bag. The lead shot are held together in a leather bag, and that helps to absorb the impacts from the hammer and distribute the impact load on the metal being worked.