For decades, one could open a Longines and expect to find a truly outstanding movement. Revered for stellar chronometres and pivotal chronographs, the name Longines was synonymous with watchmaking excellence.

As I inspect a caliber 12.68Z, one detail leaves me puzzled. Amidst the chatons, platinum timing screws, and formed springs (no wire springs to be found here), a flat hairspring sits proudly atop the balance wheel.

Prior to 1930, many Longines watches could be found with an overcoil. But from 1930 onwards, flat hairsprings became increasingly prevalent. Absent in chronographs and chronometres, one can assume that an overcoil was still preferred for superior accuracy. And yet a significant proportion of Longines watches left St. Imier without the distinctive terminal curve.

Did Longines favor longevity (i.e. formed springs, chatons, etc.) over accuracy (i.e. an overcoil) or could flat hairsprings deliver comparable rate results?

Any thoughts would be welcomed.

 

I'm bald so I'm the last one to ask about hairsprings.

 

The "breathing" of an overcoil (seen from above) is like the opening of a lotos flower!

have a nice day - h.u.

 

Interesting movement. Thank you for the link.

 

On the topic of overcoils and hairsprings, here is a helical hairspring for those interested.

 

the highest end...

 

Agreed.

 

It looks like that employs a 9-speed rear cog.

 

Sorry I don't come to the Longines forum very often, so I missed this thread earlier. I agree that there's nothing like working on a nice vintage Longines - reminds me a lot of working on a Patek or Vacheron (or even a vintage IWC). No cheap wire springs, everything is nicely finished, etc.

Although an overcoil has theoretical advantages over a flat spring, in practical terms a flat spring can be made to be very accurate - for example this ETA 7750 based Omega with regulating pins and a flat balance, with a Delta over 6 positions of less than 2 seconds:



All it needed from here was a small adjustment to average rate, and the timing was about as good as it gets. I realize this is a modern movement, but it shows what a flat spring can do.

Of course the old Longines movements that had overcoils were not free sprung balances, so they still had regulating pins that come with all the theoretical disadvantages of that system. I'm not sure you can look at just one aspect like the spring shape in isolation and make any judgments based on that. You really need to look at related developments like advances in balance wheel materials and balance spring materials that were also happening to get the full picture. Even with that, only those who made the decision at the time probably know the full details.

If you fast forward to our current times, some of the most accurate mechanical watches out there use flat balance springs, such as the new Omega watches that have silicon balance springs. The new Rolex movement is apparently moving away from an overcoil spring, using a silicon spring, while they tighten their timing specs considerably.

All watch movement designs are a series of compromises. Sometimes those are purely technical, and some are business related, but I would certainly not see any vintage Longines movement that didn't have an overcoil as being inferior really.

Cheers, Al

 

Great points Al.

Thank you very much for taking the time to respond.

 

Very interesting insights, Al. Thank you!

 

Hey Al, ever tested one of those Hamilton deck watches or marine chronometers? If so, what was your impression?

 

Sorry I don't work on clocks - I have more than enough watches to keep me busy without adding clocks to the mix!

 

Interesting, your comment about watch and clocks. Since they have a balance wheel I see these instruments more like a watch than a clock. It makes me wonder how a "watch" is defined then.

 

I know some languages use the same terms for both, but I personally consider this a clock, not a watch...



Definition of watch here...

https://en.wikipedia.org/wiki/Watch

The first line pretty much sums it up for me.

Cheers, Al

 

As would I this: