Vacheron and Constantin Mainspring

[jcrawford52]

I am cleaning a Vacheron and Constantin pocket watch (circa 1910) and don't understand the function of the cog and stop on the top of the mainspring (see photo). I have the mainspring apart, but am not sure how to set the tension when I reassemble it. When I rotate the barrel with the cog removed it puts tension on the spring, but I don't know how tight to make it. Any help appreciated.

[Bob Tascione]

Hi JCraford52,
Here's an animation I did awhile back that might be helpful.
https://learntimeonline.com/blog/geneva-stop-work/
Hope it helps,
Bob

[jcrawford52]

Bob,
What a great explanation and what a clever mechanism. I never would have figured this out for myself, but you made it very clear. Thank you very much.

[Bob Tascione]

You're very welcome JCrawford!
Glad it helped out.
Take care for now,
Bob