Help with mainspring selection.

[johnno]

Hi all

I am working on cleaning an inexpensive pocket watch with what I think is some generic name: Anti-Magnetique. I have heard of Anti-Magnetique as a concept but not as a brand.

I can’t determine what movement is in the case as there are no marking to indicate the movement name.

Anyway, I removed the mainspring from the barrel and tried to measure it as best I can and I have also used the formula to check the length of the mainspring. Using the formula I get a spring length of 566mm (so I can say 56cm) but when I stretch out the mainspring and allow for the end turn I get 54cm total length. Which method should I defer to – I guess it is possible that a shorter spring was put in last time.

Height: 2.95mm
thickness: 0.27mm
Inside Diameter of barrel: 20.82mm
Arbor diameter: 6.62mm

Can I get your thoughts on how to progress. I am just uncertain how critical this extra cm or two will be in the scheme of the age of the watch and the fact that it’s just a project.

Appreciate any assistance and thank you in advance

[Bob Tascione]

Hi Johnno,
It should be fine with that difference. The actual strength loss due to that shortage as well as the decrease in length of run time should be well within the design tolerance for that watch. I would definitely go with an alloy spring not a blue or brown high carbon steel.
There’s a website with some mainspring calculators that may come in real handy for you and others. I’ll grab the link in a bit and will post it up here for you in case you’re interested.
Hope this helps,
Back in a bit
Bob

[Bob Tascione]

Here’s that link Johnno,
Very good info here. Scroll down the page for all the different calculators you can use.
http://www.vintagewatchstraps.com/mainsprings.php
Bob

[johnno]

That’s great!

Any thoughts about the movement type? I am thinking it is European made by the name on the dial.

Thanks Bob.

[Bob Tascione]

You’re welcome Johnno,
Yes you’re correct. You have a Swiss movement there.
Nice one to get going. Have fun with it,

Bob

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