New pivot

[Tore]

Hi

I am trying to fit a new piwot in my brothers pocketwatch. I will try this before fitting a new balance staff.

During my preperations i am reading Donald de Carlos repairing book, and my understanding english i not so good.

It stands: Let the temper of the arbor down to light blue.

Does it means increase the temper to light blue with a flame,and then let it cool down?

Mvh Tore

[watchweasol]

It means reduce the temper to a light blue so as to make it able to be drilled. Normally they are hard and would not drill easily,                 Resulting in breaking or blunting the drill.             Making the staff workable     cheers

[Tore]

 Sorry for not understanding.Does that means heat the arbor up and the reduce temper of arbor to light blue. 

Tore

[HSL]

I guess one can say temper in this case just means to heat it up, since the pivot material probably earlier got heated up to quite high but a specific temperature and then quenched in water or oil just to make it harder. One could say the time it takes for a material to cool off determines its hardness.
In this case you just warm it up so it gets a light blue color and then let it cool off in air. This process makes the material softer and easier to drill.
 

[nickelsilver]

Steel (alloys that are hardenable) is hardened by heating to its critical temperature then quenching, depending on the alloy the quench may simply be ambient air, water, or oil (there are other quenches but those are the main ones).  The critical temperature for common hardenable steels is around 800 degrees C. A typical alloy used in watchmaking would be quenched in oil. When quenched, it will be fully hardened.

 

In almost all cases fully hardened steel is undesirable. To reduce the hardness it will be heated to a temperature below its critical temperature, and this is tempering. Most watch components would be tempered to a "blue" state; the tempering ideally might take several minutes or more, but the cooling off time once at color (or temp, being more scientific) is not of any great importance.

 

Blue steel is able to be filed, but not able to be sawed with normal metal cutting saw blades (this is the test some schools used to use on student work to see if they were heat treating correctly); it is also difficult to drill unless special drills are used.

 

To reduce the temper on a piece of steel it would be heated past whatever color it was originally tempered to. The color range goes: straw, brown, violet, blue, light blue, then more or less the natural steel color. When tempered to its natural color it is still harder than in the annealed state, but not generally hard enough for use.

 

To temper a watch arbor or staff, a typical technique would be to drill a piece of brass rod with an outside diameter of perhaps 3x the piece to be drilled, the drilled hole will just let the workpiece fit freely. The brass rod is heated with an alcohol flame and when the visible steel protruding from the hole is the desired color remove the rod. The steel will not cut as freely as annealed steel but much more easily than blue steel.

Edited May 16, 2020 by nickelsilver

[Tore]

Thank you very much. Very informative.

Mvh Tore

[nickelsilver]

There's a lot of mixing up of terms in steel heat treatment, even professionals who have studied it mix up hardening with tempering sometimes (it's a pet peeve of mine).

 

In my education to reduce the temper is to take the tempering to a lower state of hardness, but now thinking of it from a "blank slate" perspective it's illogical; something that is less tempered than more tempered is in effect harder!

 

At any rate, tempering can only make steel less hard, never more hard. Only heating to critical temp and quenching can increase hardness.