Setting spring replacement - heat treatment?

[Bill241]

Morning, 

I recently bought a 1920s ‘Solvil’ (Paul Ditisheim) hunter pocket watch in an English Dennison case. It has the usual Ditisheim refinements- ‘affix’ balance and alloy hairspring.

As you might expect of this type of watch, it has negative set keyless works. I immediately found that the hands would not set and so as part of the service I carry out on new acquisitions, I checked the setting spring. This has snapped and parts for these are few and far between.

I decided to make a new one- I got hold of a plate of mild steel of the same gauge (0.5mm) as the spring. The broken spring makes a handy template and is glued to the plate. I’m almost there with the cutting/drilling and will then file it and check for fit. 

Before I put it under any strain, I think I will need to harden and temper it. I’ve never done this before and would appreciate any guidance from those with experience. I’m thinking harden by heating to cherry red (800 degrees?) but how best to cool it? Oil or water? Then, temper by bluing it (295 degrees) I’m thinking of the elegant blued springs under the dial of most English pocket watches, but the original is not blued, so I can’t accurately follow the process used in its manufacture. I will probably make a set of three (a useful tip from a clockmaker!)

I’ve added some photos of the old spring in situ, and progress on the new one.

Cheers,

Bill

[Marc]

1 hour ago, Bill241 said:

I got hold of a plate of mild steel

Unfortunately if you have used mild steel you will have little hope of hardening and tempering it, it simply doesn't contain enough carbon.

You need to use a steel with a higher carbon content like tool steel or spring steel. One good source for this is engineers feeler gauges which can be picked up relatively inexpensively and provide a range of thicknesses of material. this will then harden and temper in pretty much the way you have described.

[Bill241]

Thanks Marc, clearly I have a lot to learn about metallurgy. I’d expect the cutting of tool or spring steel to be a lot harder to cut into a precise shape- I expect I’d have to anneal it first? 

[JohnR725]

9 hours ago, Marc said:

Unfortunately if you have used mild steel you will have little hope of hardening and tempering it, it simply doesn't contain enough carbon.

You need to use a steel with a higher carbon content like tool steel or spring steel. One good source for this is engineers feeler gauges which can be picked up relatively inexpensively and provide a range of thicknesses of material. this will then harden and temper in pretty much the way you have described.

over the years and various lectures I've seen it's actually quite common for people starting off making components did not to grasp that steel comes in various grades including stainless steel and they really don't harden at all. The last lecture somebody was making a part just like yours and he went into the scrap bin and grab something random I think it was packing steel in other words the blue colored Steelman put around large boxes had because was blue in color he perceived that it could be hardened. Only to discover like you that it could not be.

Then in the audience was a machine is to suggest that the exact same suggestion up above. Thinking about it I don't know if we ever got a second lecture on how well the new steel worked.

 

[Neverenoughwatches]

10 hours ago, Bill241 said:

Thanks Marc, clearly I have a lot to learn about metallurgy. I’d expect the cutting of tool or spring steel to be a lot harder to cut into a precise shape- I expect I’d have to anneal it first? 

Annealing the steel has more to it and is of more of a hit and miss process than hardening and tempering. Fun though.