The magic relationship between carbon steel and fire even after a lifetime in engineering it is still fascinating.
Heating the file to red heat and letting it cool slowly, we call this process "breaking the temper" on this side of the pond in other words returning the steel to a workable condition.
The steel is now soft enough to be worked on and cut with hand tools.
The final rough shaping before initial surface finishing
Back to the fire magic again this time we heat and rapid cool in water or oil this will make the steel glass hard. Steel in this condition is rather impractical for most purposes so tempering the steel next will give it a hardness for what we want to use it for, in this case a screwdriver blade.
Tempering small steel objects using an open flame rather than some form of constant temperature method can turn things into a form of lottery. So I will use the tried an tested method used by clockmakers for hardening small objects to a very specific hardness. Sand in a metal container and applying heat to the sand and not directly to the metal. Because sand is such a poor conductor of heat the tempering colours move over the steel surface extremely slowly enabling you to choose your required temperature and in consequence the steels hardness before you rapidly stop the process with water or oil. The sharp eyed of you will notice I used a domestic gas hob for this, because it is easy to balance the cut off bottom of a small tin filled with sand also she who must be obeyed who would put a stop to that sort of thing in her kitchen was visiting friends.
Next post the Brass parts aging and putting things together.
