My amplitude

Willbur

I know that changing the mainspring is a common practice during servicing but why is it mandatory especially when with the previous one you succeed to reach a good amplitude ?

Archer

The reason it's done is because mainsprings don't last forever, and they often fail, and can cause damage when they do. So replacing the spring (with one that is proper to the movement) is cheap insurance.

Here's a Panerai I serviced not long ago - came in with a broken mainspring. The area in the red is of note:



Closer look - you can see teeth sheared off the mainspring barrel laying on the center jewel:



Obviosuly a new barrel is required:





Here is the mainspring barrel of a Nomos watch I serviced recently - you can see the teeth aren't sheared off, but certainly damaged:



An the shock extended the damage to the center wheel:



Aside from this, the mere act of removing a mainspring from a barrel, if not done with a lot of care, can cause the spring to become out of flat. This will cause the spring to scrape the inside of the barrel, causing loss of balance amplitude, and wear on the barrel. Here's a watch where someone had clearly installed a mainspring that had been bent out of flat - even when I opened the barrel I could see the central coils were lifting out of the barrel drum. This is the spring after I removed it:



And this is what the out of flat condition did to the barrel lid - you can see the wear inside where the plating has worn off from the spring rubbing:



Mainsprings are consumables, and they wear out over time (you can often feel "waves" in the spring if you run it between your fingers), they become brittle, and become distorted from handling. No watchmaker I know of wants to have to complete a watch service over again that may be several hundreds of dollars worth of work, for the sake of a $40 spring that fails soon after they do the service.

Broken mainsprings are not rare occurrences - I get watches in all the time with broken springs.

Cheers, Al

JwRosenthal

Al, just for my curiosity and for education of others reading- does the mainspring in modern Omega’s (post ‘60’s) come as a compete assembly in a new barrel or are they like a standard mainspring that can be generically ordered and installed into a barrel assembly?

Willbur

Thanks for the explanation, I've tried to understood why teeth have been broken but I didn't find an obvious reason, kind of shock wave ?
Regarding mainspring it's written on the package "unbreakable" , so they are lying 😀