Breguet Overcoil, Advantages and Disadvantages

d3adrock · Oct 18, 2020

Hi, I've been reading up on speedmaster movements and movements in general focusing around the differences between the 321 and the 861/1861. So far the distinctions (that aren't cosmetic) I've been able to understand are
1. Column Wheel to Cam
2. Overcoil to Flat
3. Screwed balance wheel to Smooth (which somehow resulted in the increase in BPH from 18,000 to 21,600).

Since the column wheel to cam change has been talked about to death and from my understanding (feel free to disagree and explain why) doesn't affect the accuracy or performance in any regard aside from making it a bit more robust, I'd like to talk about the other two changes and find out if they can be considered improvements, or at least understanding the compromises in their design from one to the other.

Starting with the overcoil, it is my understanding (please correct me if I'm wrong) that the purpose of the overcoil is that it forces the spring to wind and unwind symmetrically and thus distributes the weight evenly across the balance wheel making it more isochronistic (or accurate in layman terms). However, one place that I'm a bit confused is that most of the mentions that I've heard in regards to improved accuracy with the overcoil mention it in conjunction with a freesprung balance as opposed to the regulated ones found in both the 321 and 861/1861. So one question I have is does an overcoil still provide any benefit in a regulated movement like the 321/861, and if so are there any disadvantages/trade offs being made? Is it a great loss to that the 861/1861 doesn't have one?

Another question I have is along the same lines as the previous one but in regards to the screwed balance wheel vs the smooth one? Since it's regulated anyways, was there ever any point in having the screws? Or if not was there any great loss going from one to the other? Any advantages or disadvantages/trade offs to having screws vs not having screws in this movement?

And finally a question that is tangential to my previous one, how does going from screws to smooth increase the beat-rate? Is there any advantage to the slightly faster beat rate or is it just incidental? Are there any tradeoffs to the faster beat rate? I know that 6 beats per second means that the chronograph seconds hand doesn't line up with the tick marks since there are 5 tickmarks and 6 beats, as opposed to the 5 beats which I assume always lined up with the tick marks. Does that matter? Am I correct?

I'd love to get y'alls opinion about this. It may sound like nitpicking but I find it interesting, i'm sure someone else out there might find it interesting too. Thanks for your help everyone!

Canuck · Oct 18, 2020

I have uploaded a picture I took some years ago, when servicing a Hamilton 992B which uses the Breguet style hairspring with overcoil. The watch belonged to a locomotive engineer (CPR) who clung to the use of his favourite railroad approved Hamilton. He had it serviced by a local “railroad watch inspector”, but the watch went back three times for regulation. They were never able to bring it to railroad standard. He asked me to look at it. The first thing I saw was the hairspring was not properly centred. So I took the hairspring off the balance wheel, and fitted it to the balance cock. You will notice that the central collet was not centred over the jewels in the cock. The overcoil hairspring allows the hairspring to “breathe” concentrically as the watch runs. Flat hairsprings tend to breathe to one side only.........the side of the hairspring 180° away from the hairspring stud. A simple adjustment to the overcoil brought the collet on centre. After the watch was conditioned and returned to the owner, it ran within seconds per week.

As to a free sprung balance as opposed to one with a typical regulator. A truly isochronal balance/hairspring is adjusted so that the location of the pinning point where the hairspring is pinned to the collet, and the outer end where the hairspring is pinned to the hairspring stud are within close parameters. Regulation on free sprung balance wheels is done by adjusting meantime screws out (to slow the watch), or in (to speed the watch up). I couldn’t say just exactly why the free sprung balance is better that one with a typical regulator.

Many modern watches which aren’t free sprung, and which use a flat hairspring, are quite capable of keeping phenomenal time.

Beats per hour are not directly related to the presence or absence of screws on the perimeter of the balance wheel. For the most part, modern watches have dispensed with screws around the perimeter of the balance wheel. And most modern watches no longer use 18,000 bph that older watches used. These screws do come in handy when it comes time to poise a balance wheel or to alter the rate, either by removing weight or adding weight.

d3adrock · Oct 18, 2020

Canuck
I have uploaded a picture I took some years ago, when servicing a Hamilton 992B which uses the Breguet style hairspring with overcoil. The watch belonged to a locomotive engineer (CPR) who clung to the use of his favourite railroad approved Hamilton. He had it serviced by a local “railroad watch inspector”, but the watch went back three times for regulation. They were never able to bring it to railroad standard. He asked me to look at it. The first thing I saw was the hairspring was not properly centred. So I took the hairspring off the balance wheel, and fitted it to the balance cock. You will notice that the central collet was not centred over the jewels in the cock. The overcoil hairspring allows the hairspring to “breathe” concentrically as the watch runs. Flat hairsprings tend to breathe to one side only.........the side of the hairspring 180° away from the hairspring stud. A simple adjustment to the overcoil brought the collet on centre. After the watch was conditioned and returned to the owner, it ran within seconds per week.

As to a free sprung balance as opposed to one with a typical regulator. A truly isochronal balance/hairspring is adjusted so that the location of the pinning point where the hairspring is pinned to the collet, and the outer end where the hairspring is pinned to the hairspring stud are within close parameters. Regulation on free sprung balance wheels is done by adjusting meantime screws out (to slow the watch), or in (to speed the watch up). I couldn’t say just exactly why the free sprung balance is better that one with a typical regulator.

Many modern watches which aren’t free sprung, and which use a flat hairspring, are quite capable of keeping phenomenal time.

Beats per hour are not directly related to the presence or absence of screws on the perimeter of the balance wheel. For the most part, modern watches have dispensed with screws around the perimeter of the balance wheel. And most modern watches no longer use 18,000 bph that older watches used. These screws do come in handy when it comes time to poise a balance wheel or to alter the rate, either by removing weight or adding weight.

So would you say that having an overcoil is beneficial regardless of whether it's freesprung or not? Any disadvantage to it? I'm trying to figure out what omega lost when it went to the 861 movement

Canuck · Oct 18, 2020

I would say that having a Breguet style overcoil would be advantageous as compared to a flat hairspring. In addition, a free sprung balance wheel/hairspring combination would eliminate any compromises to accuracy that might be instilled by having a standard regulator. Assuming of course that the watch otherwise was adjusted thoroughly to make it a precise timekeeper. Comparing an Omega calibre 861 to a finely tuned, highly precise chronometer that is adjusted to 5 or 6 positions, adjusted for isochronism, and being fitted with a Breguet hairspring, and freesprung is not possible. Two different watches with different capabilities.

As I mentioned earlier, modern high beat watches (28,800 bph or higher) can be very accurate timekeepers even if they have flat hairsprings, and are not free sprung. That is why watch manufacturers have adopted the higher frequencies on modern watches.

Archer · Oct 19, 2020

d3adrock
Is it a great loss to that the 861/1861 doesn't have one?

No, not in any true practical sense. You can get into things like how the balance spring breathes, etc., but in the end accuracy is what counts. Comparing a not even COSC certified Speedmaster movement to a Railroad grade chronometer is sort of pointless as Canuck pointed out, but the fact is that the 861/1861 movement can be very accurate, despite the fact that it has a flat balance spring, a regulator, and no balance screws.

Like most things in watch movement design, there are trade offs at play, but here's an example of an 861 I serviced recently that shows pretty clearly that you don't need an overcoil, free sprung balance, or a beat rate of 28,800 or more to get very good timing results:

Measurements at full wind over 6 positions, and below you can see the Delta (positional variation) is just 5 seconds. The average rate is +1.8 seconds per day, but of course that could be regulated closer to zero easily. I tend to leave it slightly fast because people hate a watch that runs slow, and trying to make the average rate zero is going to risk the watch running slow on the wrist if it happens to spend a lot of time in the slowest position. The beat rate here is 21,600 by the way.

So to explain, the Delta measurement is the real measure of how precise the watch is, so claims about what a watch gains over a period of time when being worn are somewhat difficult to really assess, since a watch could have a lot of variation in positions, but balance out very close to zero on the wrist (or in the pocket). Timing tests like this are way of assessing precision and accuracy while removing those variables.

To put this 5 second Delta number into perspective, Omega allows the Delta for the 861 to be as much as 25 seconds at full wind, measured over just 3 positions. So this is measured over twice the number of positions, and is 1/5th of the allowed tolerance. Note that the 1861 has a tighter tolerance for Delta, so 15 seconds over 3 positions, and this has to do with changes to the balance that were made...won't get into that detail right now.

Omega's most accurate modern watch that is METAS certified requires that the Delta at full wind is no more than 12 seconds measured over 6 positions, so this exceeds the strictest timing tolerance that Omega has. So this should pretty well answer the question of what a slower beat watch with a flat balance spring can achieve. I've has watches at 18,000 also exceed this result, so beat rate really isn't a big factor here.

I'm not saying every 861 will turn out this good, but it shows what the watch is capable of with the balance that some would say is inferior.

d3adrock
Another question I have is along the same lines as the previous one but in regards to the screwed balance wheel vs the smooth one? Since it's regulated anyways, was there ever any point in having the screws? Or if not was there any great loss going from one to the other? Any advantages or disadvantages/trade offs to having screws vs not having screws in this movement?

The screws on the 321 balance are for posing. The screws allow you to either remove or add weight as required, and without those screws the only option is to remove weight, but in practical terms it's again not really an issue. It does mean that you have to be more certain of what you are doing (you can't add material back once it's removed), but anyone who is competent at poising isn't going to find this any sort of major hurdle to overcome.

I can recall maybe once or twice being limited in how much posing I could do, as the balance amplitude was already very high, and removing more weight would risk rebanking, but that is a rare thing.

Anyway, hope this helps.

Cheers, Al

d3adrock · Oct 19, 2020

Archer
Like most things in watch movement design, there are trade offs at play, but here's an example of an 861 I serviced recently that shows pretty clearly that you don't need an overcoil, free sprung balance, or a beat rate of 28,800 or more to get very good timing results:

I'm not saying every 861 will turn out this good, but it shows what the watch is capable of with the balance that some would say is inferior.

Note that the 1861 has a tighter tolerance for Delta, so 15 seconds over 3 positions, and this has to do with changes to the balance that were made...won't get into that detail right now.

The screws on the 321 balance are for posing. The screws allow you to either remove or add weight as required, and without those screws the only option is to remove weight, but in practical terms it's again not really an issue. It does mean that you have to be more certain of what you are doing (you can't add material back once it's removed), but anyone who is competent at poising isn't going to find this any sort of major hurdle to overcome.

That does help, thank you greatly for sharing your knowledge!

Would you be willing to go more in depth as to the trade offs at play in these differences?

When you say that some would consider it inferior, do you think it is?

When you say that the 1861 has a tighter tolerance for delta because of changes to the balance that were made, I would really like it if you did go more into that sort of detail as that's exactly what I'm interested in knowing!

Is there anything gained by going to a smooth balance wheel then if it doesn't pose an issue in poising?

Thanks again!

Archer · Oct 19, 2020

d3adrock
Would you be willing to go more in depth as to the trade offs at play in these differences?

This sort of discussion would require a full textbook to get through it all. There are so many variables at play that condensing this down to a few paragraphs is nearly impossible.

d3adrock
When you say that some would consider it inferior, do you think it is?

Again, a ton of variables, so the answer is "it depends"...

Watch movements are designed as systems, not as individual parts thrown in together...

d3adrock
When you say that the 1861 has a tighter tolerance for delta because of changes to the balance that were made, I would really like it if you did go more into that sort of detail as that's exactly what I'm interested in knowing!

Changes were made in the formation of the terminal curve that goes through the regulator and where it connects to the stud. The older style was a double bend, and the newer style is a single bend. This reduces the complexity of the spring in this area and the chances of distortion, and reduces the distance from the center of the balance to the stud.

The terminal curve is also heat treated in the new design, where the older design is not. Thermal treatment of the terminal curve is a technological advance that allows this area of the spring to be made stiffer, without making any changes in the mass of the spring. Many modern balance springs made by Swatch (Nivarox FAR) have used this technology as a means to improve accuracy. You can sometimes make it out as a slight yellow tinge to the spring right near the stud.

d3adrock
Is there anything gained by going to a smooth balance wheel then if it doesn't pose an issue in poising?

Yes, less mass and less drag. The screws added to the outside diameter of the balance add drag - they slow the balance down due to having to move through the air. In addition, lower mass means that rate recovery in the event of a disturbance to the balance is faster.

This also requires less force to propel the balance, so a mainspring with lower toque can be used, saving wear and tear on the movement.

d3adrock · Oct 19, 2020

Archer
This sort of discussion would require a full textbook to get through it all. There are so many variables at play that condensing this down to a few paragraphs is nearly impossible.

Again, a ton of variables, so the answer is "it depends"...

Watch movements are designed as systems, not as individual parts thrown in together...

Changes were made in the formation of the terminal curve that goes through the regulator and where it connects to the stud. The older style was a double bend, and the newer style is a single bend. This reduces the complexity of the spring in this area and the chances of distortion, and reduces the distance from the center of the balance to the stud.

The terminal curve is also heat treated in the new design, where the older design is not. Thermal treatment of the terminal curve is a technological advance that allows this area of the spring to be made stiffer, without making any changes in the mass of the spring. Many modern balance springs made by Swatch (Nivarox FAR) have used this technology as a means to improve accuracy. You can sometimes make it out as a slight yellow tinge to the spring right near the stud.

Yes, less mass and less drag. The screws added to the outside diameter of the balance add drag - they slow the balance down due to having to move through the air. In addition, lower mass means that rate recovery in the event of a disturbance to the balance is faster.

This also requires less force to propel the balance, so a mainspring with lower toque can be used, saving wear and tear on the movement.

Awesome! That's exactly the type of info I was looking for, thank you!

Would you say that with these advances in technology (nivarox FAR) sort of equal out with the advantages of an overcoil? Or would you say that they improve on it in some other category, such as the flat balancespring being more durable than one with an overcoil?

Archer · Oct 19, 2020

d3adrock
Would you say that with these advances in technology (nivarox FAR) sort of equal out with the advantages of an overcoil? Or would you say that they improve on it in some other category, such as the flat balancespring being more durable than one with an overcoil?

I'll give you some additional information, and you can draw your own conclusions...

For the Cal. 321 the timing tolerances are as follows:

Delta over 3 positions at full wind allowed to be as much as 20 seconds.

Delta over 3 positions 24 hours after full wind allowed to be as much as 30 seconds.

Tolerance for average daily rate is that it should fall between -1 and +16 seconds per day.

For the Cal. 1861 the timing tolerances are as follows:

Delta over 3 positions at full wind allowed to be as much as 15 seconds.

Delta over 3 positions 24 hours after full wind allowed to be as much as 20 seconds.

Tolerance for average daily rate is that it should fall between -1 and +11 seconds per day.

d3adrock · Oct 19, 2020

Archer
I'll give you some additional information, and you can draw your own conclusions...

For the Cal. 321 the timing tolerances are as follows:

Delta over 3 positions at full wind allowed to be as much as 20 seconds.

Delta over 3 positions 24 hours after full wind allowed to be as much as 30 seconds.

Tolerance for average daily rate is that it should fall between -1 and +16 seconds per day.

For the Cal. 1861 the timing tolerances are as follows:

Delta over 3 positions at full wind allowed to be as much as 15 seconds.

Delta over 3 positions 24 hours after full wind allowed to be as much as 20 seconds.

Tolerance for average daily rate is that it should fall between -1 and +11 seconds per day.

Thank you, that does speak for itself, if nothing else that really puts in perspective just how accurate the 861 is and how far the movements have come.

In trying to understand the move from the overcoil in the 321 to the flat spring in the 861, since obviously accuracy is not an improvement, do you know if any other advantages outside of accuracy are brought about by an flat balancespring? Perhaps durability or added shock resistance?

Also this is an aside question but do you have any idea or know what the naming of the moments corresponds too in regards to 321 and 861? Are they named from some obscure mechanical feature or is it totally arbitrary?

Thanks you for taking the time to educate a young watch enthusiast in the technical aspects of movements. I really appreciate it. It's truly so amazing to have people like you willing to share their knowledge and expertise for free to complete strangers.

Archer · Oct 20, 2020

No ideas how Omega assigns caliber designations.

The balance spring being flat has advantages in manufacturing cost, as it is less expensive to make. It also takes up less vertical space, so saves on thickness. That being said on a chronograph movement the overall thickness is determined by other parts.

Breguet Overcoil, Advantages and Disadvantages

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