# What makes the Speedmaster movement any good?



## Runitout

I've done a forum search, and found nothing that answers this question. So excuse me if this has been asked before:

_What makes the Speedmaster movement any good?_

The Lemania 2310/1873 family of movements, installed in the current Speedmaster as the Omega cal. 1861, has an excellent reputation. It's really (apart from the marketing gub) the strength of the watch. By comparison, the Speedmaster Reduced (when it existed) was maligned, in part because it only had a lowly Eta 2894, whereas the Speedy Pro boasted the Lemania calibre. Similarly, the Breitling Navitimer or Speedy Date is often derided when compared to Speedmaster Pro for its use of the Valjoux (along with just about every Swiss chronograph under $5000).

I own one of these Lemania movements, albeit in a Sinn 903 with the moonphase and date complication (cal 1883/omega cal 1866). I've never before doubted that that the Lemania movement was a superior one to its competition. It certainly is a lot prettier than a 7750, or 2894, or 5100. But in its current iteration, it doesn't have a column wheel, or a free sprung balance, or a Breguet overcoil or or Lossier innercoil. It's not a highbeat movement. It has no date, power reserve, or automatic winding. So what makes it better than, say a 6s37 or 6s28 with column wheel and vertical clutch? Or even a 7750?

I'm genuinely curious; as I don't have the wit or horological knowledge to find out myself - can anyone tell me the answer?


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## Ozy

Runitout said:


> I've done a forum search, and found nothing that answers this question. So excuse me if this has been asked before:
> 
> _What makes the Speedmaster movement any good?_
> 
> The Lemania 2310/1873 family of movements, installed in the current Speedmaster as the Omega cal. 1861, has an excellent reputation. It's really (apart from the marketing gub) the strength of the watch. By comparison, the Speedmaster Reduced (when it existed) was maligned, in part because it only had a lowly Valjoux 7750, whereas the Speedy Pro boasted the Lemania calibre. Similarly, the Breitling Navitimer is often derided when compared to Speedmaster for its use of the Valjoux (along with just about every Swiss chronograph under $5000).
> 
> I own one of these Lemania movements, albeit in a Sinn 903 with the moonphase and date complication (cal 1883/omega cal 1866). I've never before doubted that that the Lemania movement was a superior one to its competition. It certainly is a lot prettier than a 7750, or 2894, or 5100. But in its current iteration, it doesn't have a column wheel, or a free sprung balance, or a Breguet overcoil or or Lossier innercoil. It's not a highbeat movement. It has no date, power reserve, or automatic winding. So what makes it better than, say a 6s37 or 6s28 with column wheel and vertical clutch? Or even a 7750?
> 
> I'm genuinely curious; as I don't have the wit or horological knowledge to find out myself - can anyone tell me the answer?


Sometimes, its everything an object lacks that makes it good at what it does. Sure, it isnt the most technologically advanced movement, highly decorated, or overly complicated - but i'll be damned if it doesnt bring a smile every morning I wind it.


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## wjk_glynn

By modern standards, it's nothing special from a horological perspective.

But ‘back in the day’ it proved (through rigorous NASA testing) to be a highly robust watch with the original c321 movement. It was present and even participated in certain pivotal moments of the Mercury-through-Apollo programs. Not an example of high horology, but it’s the one you’d want if you had to manually time a rocket burn to get you back to planet Earth. So its history is what makes it significant, at least to me.

And the fact that you can still buy a 3570.50 today with an 1861 movement (an evolution of the 321 with some manufacturing/servicing simplifications and accuracy improvements, but still closely related to the original 321) and whose case/dial/crystal are quite similar (with some detail differences) to the 105.012 / 145.012 references… I think that’s pretty cool :-!

Karl.


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## richardew

I have 4. They are 1, 18, 43 and 46 years old. They run and they run and they run and they run and they run........and they run...and they run....and they run....


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## apropos

IDK, as far as I can see all answers have been appeals to sentimentality than actual answers to the OP's query.

Still hopeful someone might step up to the plate.


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## CCJ

The 861 was tested by NASA twice, in the same types of conditions as the first tests with the 321. So setting aside the history of the watch, there is the practical aspect that the modern 1861 (which is only a slight variation of the 861) is one of the most proven movements in the world. Even if you never need to take your watch to such extremes, you can be more confident in the durability of this movement than just about any other.


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## tattoodobem

Isn't the 1861 more accurate? see this thread: https://www.watchuseek.com/f21/6s37-accuracy-180743.html

people talk about +3 +4 seconds, while for 1861 people talk about +2.
And which one is easier to repair? it's said the 1861 is great to repair what about the 6s37?


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## Majh

Simplicity, reliability and accuracy that is still satisfactory.


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## Moon Mullins

wjk_glynn said:


> By modern standards, it's nothing special from a horological perspective.
> 
> But 'back in the day' it proved (through rigorous NASA testing) to be a highly robust watch with the original c321 movement. It was present and even participated in certain pivotal moments of the Mercury-through-Apollo programs. Not an example of high horology, but it's the one you'd want if you had to manually time a rocket burn to get you back to planet Earth. So its history is what makes it significant, at least to me.
> 
> And the fact that you can still buy a 3570.50 today with an 1861 movement (an evolution of the 321 with some manufacturing/servicing simplifications and accuracy improvements, but still closely related to the original 321) and whose case/dial/crystal are quite similar (with some detail differences) to the 105.012 / 145.012 references&#8230; I think that's pretty cool :-!
> 
> Karl.


Everything that Karl said!


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## Hansch99

richardew said:


> I have 4. They are 1, 18, 43 and 46 years old. They run and they run and they run and they run and they run........and they run...and they run....and they run....


I've had three, and two of them weren't as lucky. And unfortunately, they were problematic well within the recommended service interval. I haven't been as impressed with the movement, quite frankly.


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## pgrivas

I am new to watch collecting and just picked up a brand new sapphire sandwich Speedy. Unfortunately it's running about 25 seconds fast per day.  I've read to maybe wait a month before having it serviced. Does that seem like the right thing to do?


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## geremy

with or without the chronograph running? (not that it's important, I'm just curious). Mine is 5 years old and has always been +5 fast per day.


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## pgrivas

geremy said:


> with or without the chronograph running? (not that it's important, I'm just curious). Mine is 5 years old and has always been +5 fast per day.


I tested it for 5 days without and it ran about +20 secs/day. Testing it again for 4 days with the chronograph running it's now runs about +25 secs/day. I tried leaving it off face up, face down, resting on the crown, resting on the other side, etc, etc and it always runs fast.

BTW, I did buy it from an AD.


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## Kringkily

pgrivas said:


> I tested it for 5 days without and it ran about +20 secs/day. Testing it again for 4 days with the chronograph running it's now runs about +25 secs/day. I tried leaving it off face up, face down, resting on the crown, resting on the other side, etc, etc and it always runs fast.
> 
> BTW, I did buy it from an AD.


Could just need a simple regulation. Bring it into a watch maker and they can diagnose what might be your problem.


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## jswing

pgrivas said:


> I tested it for 5 days without and it ran about +20 secs/day. Testing it again for 4 days with the chronograph running it's now runs about +25 secs/day. I tried leaving it off face up, face down, resting on the crown, resting on the other side, etc, etc and it always runs fast.
> 
> BTW, I did buy it from an AD.


I'd take it back to the AD to have it regulated. That's too far out of whack.


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## Jade330i

jswing said:


> I'd take it back to the AD to have it regulated. That's too far out of whack.


Agreed....they will be able to fix that lickity-split.....I have one that's just a few months old and it's running -2sec. per day after being regulated.


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## whitestripes

wjk_glynn said:


> And the fact that you can still buy a 3570.50 today with an 1861 movement* (an evolution of the 321 with some manufacturing/servicing simplifications and accuracy improvements, but still closely related to the original 321)* and whose case/dial/crystal are quite similar (with some detail differences) to the 105.012 / 145.012 references&#8230; I think that's pretty cool :-!


While I think the 1861 is a great movement, I don't believe it's an evolution of the 321. The 321 was a column wheel, 861 a cam/lever chronograph. Column wheel is more expensive to manufacture, but I think it has a nicer push to the buttons (wouldn't know, have only owned an 1861). It's also the one used in ALL high end chronographs. What would be nice is a vertical clutch, which would eliminate the little jump when you start the chrono. Anyway, an evolution would be something similar to the previous generation with some tweaks. Getting rid of the column wheel makes it a completely different class of chronographs.
Please read this informative post:

Tick Talk » Omega Calibre 321 and "The Good Old Days"


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## M4tt

I assume that you have read this:

http://omega.watchprosite.com/show-nblog.post/ti-364597/

While it doesn't particularly make the case for the excellence of the movement, it's really rather interesting. Personally I have one of the Lemania versions with what would, in Omega, be called a 320 movement. Mine is over sixty years old and still going strong. As I never get bored of asserting, every watch movement is a nest of compromises. I suspect that the secret of the Lemania 321 and 861 movements is that they balance these compromises particularly well. The consequence is a movement with no real weaknesses and many real strengths. With over seventy years of development behind it, this movement family has gently evolved into one that is hard to break, easy to fix, stable enough to pass COSC (864) with fettling, robust, tolerant of abuse and very long lived.


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## Goose

jswing said:


> I'd take it back to the AD to have it regulated. That's too far out of whack.


+1. You'll be bummed waiting for it to come back if they send it out. But worth the wait. 
Or, ask for an exchange.

I've had two. First was about -5s/24hr. One I've now is about 25 yrs old. Runs consistent at -2s/24hr.

I don't know the internals enough to detail mov't specifics as to why it's what it is. I do know that I've two watches about the same age. My other is a 1985 Rolex Datejust at -2s/24hr. And, my non-COSC Speedy is more accurate after 24hrs than my 7 yr old Breitling and Rolex GMTII.

While, certainly, sentiment plays a role, I too wish to learn why this watch is what it is.


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## Runitout

Thanks for all the replies!



M4tt said:


> I assume that you have read this:
> 
> http://omega.watchprosite.com/show-nblog.post/ti-364597/
> 
> While it doesn't particularly make the case for the excellence of the movement, it's really rather interesting. Personally I have one of the Lemania versions with what would, in Omega, be called a 320 movement. Mine is over sixty years old and still going strong. As I never get bored of asserting, every watch movement is a nest of compromises. I suspect that the secret of the Lemania 321 and 861 movements is that they balance these compromises particularly well. The consequence is a movement with no real weaknesses and many real strengths. With over seventy years of development behind it, this movement family has gently evolved into one that is hard to break, easy to fix, stable enough to pass COSC (864) with fettling, robust, tolerant of abuse and very long lived.


Thanks M4tt; I was rather hoping for your input.

I've not seen that article before. It is, as you say, a very interesting article, which I will have to read a few times, I think, to really appreciate its content.

I think what I would like to know is what is it exactly that the 1873/861 does that is better than, say, a 7750? Apart from having a face only a mother can love, and winding like a unoiled bike chain, I'm not aware of any functional or structural issues with the 7750 that would lead me to believe that it is a worse solution to the necessary compromises you refer to than the Lemania is. What strengths or weaknesses are present in the Lemania that the Valjoux doesn't exhibit?

I know that the Lemania is a robust, dependable, extremely durable and mostly accurate mechanical chronograph movement. But there are others, and those others are often both much less expensive and (for reasons I don't understand) much more poorly regarded. Apart from exclusivity, or sentiment, or which constellation it has visited, I'm just trying to find out why it is that the Lemania has that superior reputation.


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## Runitout

whitestripes said:


> While I think the 1861 is a great movement, I don't believe it's an evolution of the 321. The 321 was a column wheel, 861 a cam/lever chronograph. Column wheel is more expensive to manufacture, but I think it has a nicer push to the buttons (wouldn't know, have only owned an 1861). It's also the one used in ALL high end chronographs. What would be nice is a vertical clutch, which would eliminate the little jump when you start the chrono. Anyway, an evolution would be something similar to the previous generation with some tweaks. Getting rid of the column wheel makes it a completely different class of chronographs.
> Please read this informative post:
> 
> Tick Talk » Omega Calibre 321 and "The Good Old Days"


Thanks whitestripes. It's funny how we think of the mechanisation of watch movement production being a post-quartz cost-cutting thing, when it was well under way in the 1960s. The flat balance spring, cam lever and (allegedly) different steel testify to that.


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## wjk_glynn

whitestripes said:


> While I think the 1861 is a great movement, I don't believe it's an evolution of the 321. The 321 was a column wheel, 861 a cam/lever chronograph...


That's a fair point. Maybe the analogy is the 'evolution' of the Porsche 911 from air/oil-cooled to water-cooled ;-).

Karl.


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## M4tt

The 7750 is as good an example of one nest of compromises as any. Forgetting about construction, just think about how fast one ticks relative to the other. 

So, the 7750 ticks at 28,000. This in itself is a complex compromise. it's reasonably well understood that the advantage of this is increased stability for a given level of poising and so on. However the cost is that it uses energy more rapidly, this means you have to balance several other compromises. You could reduce the reserve or you can increase the strength of the spring. With around a 46 hour reserve, it is pretty clear the choice taken here. This means that there is going to be more torque available. This seems great, but the place at which the power in the spring is turned into timekeeping is the balance and that means that all the components between the balance and the mainspring have to continuously cope with the lateral forces produced by the spring and kept in check by the escapement - everything is under a great deal of tension and this is a recipe for increased wear on pivots, jewels, teeth and so on.

The Speedmaster, on the other hand, beats at a far more relaxed rate and is far less stressed: 18,000 and a 44 hour reserve for the 321 and 21,600 and a forty hour reserve for the 861 family. Notice that when Omega increased the beat rate they kept the spring the same and allowed the reserve to drop. You don't need to do the maths to realise that the Lemania calibre is far, far less stressed. This has a range of advantages, not least long term robustness and the ability to cope with less than impeccable servicing. Obviously, this involves other smaller compromises to do with the size of the balance and so on...

Obviously materials technology has improved somewhat, but the real point is this: in watches available on the high street, which is the more stable and thus potentially accurate watch? I may be wrong, but I don't think that many people will be able to say. Which watch is going to last the longer is a damn sight clearer. On paper, all things being equal, the 7750 should be more accurate, but I'm pretty sure most people's experience will not bear this out. There's a reason for this, it's another compromise: slower beat watches simply need more work in the factory to make them as stable as higher beat watches. The main reason that highbeat watches are the norm is because they reduce the need for careful poising and balancing which is usually labour intensive and thus expensive. They could be more accurate in principle, but their improved stability is just a way of reducing manufacturing costs by passing the wear (the other side of that compromise) to the consumer. 

So, if you are after a watch to last a real lifetime or two...

(Pm answer coming when I get another spare minute!)


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## KatGirl

M4tt said:


> The 7750 is as good an example of one nest of compromises as any. Forgetting about construction, just think about how fast one ticks relative to the other.
> 
> So, the 7750 ticks at 28,000. This in itself is a complex compromise. it's reasonably well understood that the advantage of this is increased stability for a given level of poising and so on. However the cost is that it uses energy more rapidly, this means you have to balance several other compromises. You could reduce the reserve or you can increase the strength of the spring. With around a 46 hour reserve, it is pretty clear the choice taken here. This means that there is going to be more torque available. This seems great, but the place at which the power in the spring is turned into timekeeping is the balance and that means that all the components between the balance and the mainspring have to continuously cope with the lateral forces produced by the spring and kept in check by the escapement - everything is under a great deal of tension and this is a recipe for increased wear on pivots, jewels, teeth and so on.
> 
> The Speedmaster, on the other hand, beats at a far more relaxed rate and is far less stressed: 18,000 and a 44 hour reserve for the 321 and 21,600 and a forty hour reserve for the 861 family. Notice that when Omega increased the beat rate they kept the spring the same and allowed the reserve to drop. You don't need to do the maths to realise that the Lemania calibre is far, far less stressed. This has a range of advantages, not least long term robustness and the ability to cope with less than impeccable servicing. Obviously, this involves other smaller compromises to do with the size of the balance and so on...
> 
> Obviously materials technology has improved somewhat, but the real point is this: in watches available on the high street, which is the more stable and thus potentially accurate watch? I may be wrong, but I don't think that many people will be able to say. Which watch is going to last the longer is a damn sight clearer. On paper, all things being equal, the 7750 should be more accurate, but I'm pretty sure most people's experience will not bear this out. There's a reason for this, it's another compromise: slower beat watches simply need more work in the factory to make them as stable as higher beat watches. The main reason that highbeat watches are the norm is because they reduce the need for careful poising and balancing which is usually labour intensive and thus expensive. They could be more accurate in principle, but their improved stability is just a way of reducing manufacturing costs by passing the wear (the other side of that compromise) to the consumer.
> 
> So, if you are after a watch to last a real lifetime or two...
> 
> (Pm answer coming when I get another spare minute!)


You know what?.....I a_lmost_ understood that............ Like the OP, I was waiting for M4tt to comment on this thread.


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## Archer

M4tt said:


> The 7750 is as good an example of one nest of compromises as any. Forgetting about construction, just think about how fast one ticks relative to the other.
> 
> So, the 7750 ticks at 28,000. This in itself is a complex compromise. it's reasonably well understood that the advantage of this is increased stability for a given level of poising and so on. However the cost is that it uses energy more rapidly, this means you have to balance several other compromises. You could reduce the reserve or you can increase the strength of the spring. With around a 46 hour reserve, it is pretty clear the choice taken here. This means that there is going to be more torque available. This seems great, but the place at which the power in the spring is turned into timekeeping is the balance and that means that all the components between the balance and the mainspring have to continuously cope with the lateral forces produced by the spring and kept in check by the escapement - everything is under a great deal of tension and this is a recipe for increased wear on pivots, jewels, teeth and so on.
> 
> The Speedmaster, on the other hand, beats at a far more relaxed rate and is far less stressed: 18,000 and a 44 hour reserve for the 321 and 21,600 and a forty hour reserve for the 861 family. Notice that when Omega increased the beat rate they kept the spring the same and allowed the reserve to drop. You don't need to do the maths to realise that the Lemania calibre is far, far less stressed. This has a range of advantages, not least long term robustness and the ability to cope with less than impeccable servicing. Obviously, this involves other smaller compromises to do with the size of the balance and so on...
> 
> Obviously materials technology has improved somewhat, but the real point is this: in watches available on the high street, which is the more stable and thus potentially accurate watch? I may be wrong, but I don't think that many people will be able to say. Which watch is going to last the longer is a damn sight clearer. On paper, all things being equal, the 7750 should be more accurate, but I'm pretty sure most people's experience will not bear this out. There's a reason for this, it's another compromise: slower beat watches simply need more work in the factory to make them as stable as higher beat watches. The main reason that highbeat watches are the norm is because they reduce the need for careful poising and balancing which is usually labour intensive and thus expensive. They could be more accurate in principle, but their improved stability is just a way of reducing manufacturing costs by passing the wear (the other side of that compromise) to the consumer.
> 
> So, if you are after a watch to last a real lifetime or two...
> 
> (Pm answer coming when I get another spare minute!)


Hi Matt,

I have to jump in here to comment on a few things....

7750 = 28,800, not 28,000 - I assume this was just a typo.

Regarding the run time and what needs to happen with the spring for a faster beat rate, it's not necessarily the strength that increases, but the length. For example for the Cal. 321 the mainspring is some 13.5 inches long, where the 7750 spring is more like 23+ inches long. Strength does not enter the equation with all else being equal.

Now regarding strength, looking at mainspring sizes, the 7750 spring is a little bit wider, at 1.5 mm instead of 1.3 for the 321. Increse in strength is proprotional to the width, so this is about 15% stronger. However, the thickness of the 7750 is less than for the 321. The 321 is 0.13, where the 7750 is 0.11, and since thickess increses or decreses strength cubed, this has much more impact than width does. So if I have my numbers straight the strength of the 7750 based on thickess alone is something like 62% of the 321, so the two together would result in a spring in the 7750 that is maybe 90% or so as strong as the 321....someone needs to check my calcs but the fundamental point is that the 7750 does not need more strength, but more length.

Regarding performance, I service a lot of ETA 7750 based watches and also a lot of 321, 861, and 1861 based Speedmasters. I can tell you without a doubt that on average the 7750 based watches are far better timekeepers, even those that are not COSC certified. You have to remember to take the "on-wrist" performance people report with a grain of salt. Not because you can't trust what they are saying, but because performance measured this way is very crude from a watchmaking perspective, even though it is the most important thing to the watch owner. To truly understand how a watch is performing, you need to see how it runs in positions on a timing machine, because on the wrist these things can balance out to be very close, even though the positional variation is quite high.

BTW faster beat rate does have distinct advantages both in static situations as you describe, but also for rate recovery after the balance has been disturbed from moving your wirst. No doubt a slow beat watch can be dialed in to be very accurate with static and dynamic poising, etc., but that really doesn't help rate recovery.

Personally I don't think the 7750 family gets the respect it deserves, maybe because it's so common. It's a robust movement that runs well, has great accuracy, and is very serviceable.

Hope this helps.

Cheers, Al


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## M4tt

> Hi Matt,
> 
> I have to jump in here to comment on a few things....


That's always welcome, you know far more than I do.



> 7750 = 28,800, not 28,000 - I assume this was just a typo.


Yup.



> Regarding the run time and what needs to happen with the spring for a faster beat rate, it's not necessarily the strength that increases, but the length. For example for the Cal. 321 the mainspring is some 13.5 inches long, where the 7750 spring is more like 23+ inches long. Strength does not enter the equation with all else being equal.


That's fine, my point was about the output of the entire going barrel causing increased wear due to there being more torque. As you must be fully aware, in the sort of going barrel used in both watches, not all of the length of the mainspring is actually used and so I'm not sure if all else is equal because I'm not sure how the pre-tensioning is implemented and thus how much of the length is functional rather than there to flatten the torque curve. Perhaps you are, in which case I would be really keen to be offered a comparison. However, this is largely academic as ultimately the question is how much torque is generated by the barrel when fully wound and thus how much stress the going train is under.



> Now regarding strength, looking at mainspring sizes, the 7750 spring is a little bit wider, at 1.5 mm instead of 1.3 for the 321. Increse in strength is proprotional to the width, so this is about 15% stronger. However, the thickness of the 7750 is less than for the 321. The 321 is 0.13, where the 7750 is 0.11, and since thickess increses or decreses strength cubed, this has much more impact than width does. So if I have my numbers straight the strength of the 7750 based on thickess alone is something like 62% of the 321, so the two together would result in a spring in the 7750 that is maybe 90% or so as strong as the 321....someone needs to check my calcs but the fundamental point is that the 7750 does not need more strength, but more length.


I'm sure that you are quite right about these dimensions. However, my point was fundamentally about more torque causing more wear in highbeat movements. I am sure that you are spot on about the characteristics of the spring in the 321 compared to the 7750. However, your apparent conclusion, that the going train in the 7750 is actually handling less torque and is consequently less stressed than the going train in the 321 is one that is intensely surprising to me. Hopefully, rather than getting tied up in the maths, this focusses the point at which you appear to be asserting that I am in error. If it is indeed the case that, all things being equal, a highbeat movement with a longer reserve can be under less stress than a lowbeat movement with a shorter reserve then what I asserted is clearly wrong. Are you saying that this is the case?

BTW, I am fully aware of this discussion:

https://www.watchuseek.com/f2/36-000-bph-reliability-632479.html

But can't help feeling that Lysander is pushing an exception rather than a rule.



> Regarding performance, I service a lot of ETA 7750 based watches and also a lot of 321, 861, and 1861 based Speedmasters. I can tell you without a doubt that on average the 7750 based watches are far better timekeepers, even those that are not COSC certified. You have to remember to take the "on-wrist" performance people report with a grain of salt. Not because you can't trust what they are saying, but because performance measured this way is very crude from a watchmaking perspective, even though it is the most important thing to the watch owner.


Quite so - when you are working out the compromises for a tool watch that is designed to measure up to twelve hours, I'd say that sufficient accuracy to get a reputation for accuracy among owners is really what you would be aiming for?



> To truly understand how a watch is performing, you need to see how it runs in positions on a timing machine, because on the wrist these things can balance out to be very close, even though the positional variation is quite high.


I quite agree, but I'm not sure that this is the concern of owners here. I can get extremely excited about precision in HEQ or chronometers, but that's just not what I'm looking for in the Speedmaster.



> BTW faster beat rate does have distinct advantages both in static situations as you describe, but also for rate recovery after the balance has been disturbed from moving your wirst. No doubt a slow beat watch can be dialed in to be very accurate with static and dynamic poising, etc., but that really doesn't help rate recovery.


True, I am not denying that highbeat watches can be more accurate, I'm asserting that they are not regulated to take full advantage of this due as it is a way tocur production costs. As such, the average Speedmaster at point of sale will had more effort - and thus expense - put into poising and balancing than the average 7750.



> Personally I don't think the 7750 family gets the respect it deserves, maybe because it's so common. It's a robust movement that runs well, has great accuracy, and is very serviceable.


Personally I prefer the 1340, but I'm not disagreeing. I'm just not sure how well they will do in the very long run - I guess we will see one day.

Either way, thanks for the detailed response. At worst I'm being pushed to write more carefully and precisely, which is no bad thing. At best I'm getting something horribly wrong and being quite sure that I'm right and so I really would value a deeper explanation if I have been under what looks to be a pretty common misconception for decades.

Cheers Al,

Matt


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## drewmcd24

M4tt said:


> The Speedmaster, on the other hand, beats at a far more relaxed rate and is far less stressed: 18,000 and a 44 hour reserve for the 321 and 21,600 and a forty hour reserve for the 861 family.


Very interesting post, thanks a lot. Doesn't the 1861 movement have a 48 hour power reserve though?



Archer said:


> Hi Matt,
> 
> I have to jump in here to comment on a few things....
> 
> 7750 = 28,800, not 28,000 - I assume this was just a typo.
> 
> Regarding the run time and what needs to happen with the spring for a faster beat rate, it's not necessarily the strength that increases, but the length. For example for the Cal. 321 the mainspring is some 13.5 inches long, where the 7750 spring is more like 23+ inches long. Strength does not enter the equation with all else being equal.
> 
> Now regarding strength, looking at mainspring sizes, the 7750 spring is a little bit wider, at 1.5 mm instead of 1.3 for the 321. Increse in strength is proprotional to the width, so this is about 15% stronger. However, the thickness of the 7750 is less than for the 321. The 321 is 0.13, where the 7750 is 0.11, and since thickess increses or decreses strength cubed, this has much more impact than width does. So if I have my numbers straight the strength of the 7750 based on thickess alone is something like 62% of the 321, so the two together would result in a spring in the 7750 that is maybe 90% or so as strong as the 321....someone needs to check my calcs but the fundamental point is that the 7750 does not need more strength, but more length.
> 
> Regarding performance, I service a lot of ETA 7750 based watches and also a lot of 321, 861, and 1861 based Speedmasters. I can tell you without a doubt that on average the 7750 based watches are far better timekeepers, even those that are not COSC certified. You have to remember to take the "on-wrist" performance people report with a grain of salt. Not because you can't trust what they are saying, but because performance measured this way is very crude from a watchmaking perspective, even though it is the most important thing to the watch owner. To truly understand how a watch is performing, you need to see how it runs in positions on a timing machine, because on the wrist these things can balance out to be very close, even though the positional variation is quite high.
> 
> BTW faster beat rate does have distinct advantages both in static situations as you describe, but also for rate recovery after the balance has been disturbed from moving your wirst. No doubt a slow beat watch can be dialed in to be very accurate with static and dynamic poising, etc., but that really doesn't help rate recovery.
> 
> Personally I don't think the 7750 family gets the respect it deserves, maybe because it's so common. It's a robust movement that runs well, has great accuracy, and is very serviceable.
> 
> Hope this helps.
> 
> Cheers, Al


Very interesting, thanks a lot for your comments.


----------



## M4tt

> Very interesting post, thanks a lot. Doesn't the 1861 movement have a 48 hour power reserve though?


Thanks, but I'd wait and see how the conversation with Archer plays out to see if my argument has a gaping hole in the middle of it!:-d


> Doesn't the 1861 movement have a 48 hour power reserve though?


I referenced the 861 family as they are the most representative and, according to the good Doctor Ranfft:

bidfun-db Archive: Watch Movements: Omega 861 (Lemania 1873)

It's forty.

We may both be wrong...


----------



## Archer

M4tt said:


> Thanks, but I'd wait and see how the conversation with Archer plays out to see if my argument has a gaping hole in the middle of it!:-d
> 
> I referenced the 861 family as they are the most representative and, according to the good Doctor Ranfft:
> 
> bidfun-db Archive: Watch Movements: Omega 861 (Lemania 1873)
> 
> It's forty.
> 
> We may both be wrong...


It's 45 per the Omega tech guides.

Cheers, Al


----------



## Archer

Matt - here's what you said in your initial post:

"However the cost is that it uses energy more rapidly, this means you have to balance several other compromises. You could reduce the reserve or you can increase the strength of the spring."

This is not true as I've stated. Power reserve is a function of mainspring length and beat rate. Strength of the mainspring has nothing to do with it.

I have no idea what pretensioning is that you are referring to, and why you are saying the the entire length of the spring is not used - there is no geneva stopworks or similar mechanism in these calibers. The spring is used as much as in any watch, and the springs are the same modern shape. But I can say that torque comes from one place - the mainspring. If the mainspring is weaker, it puts less torque into the train.

In fact, because the bridle slips in a 7750 (automatic) the torque curve is likely flatter than it is in the manual wind watches, at least for the first hour or so.

Anyway, dinner is waiting so I don't have time to write more - going back to work after I eat.

Cheers, Al


----------



## M4tt

Archer said:


> It's 45 per the Omega tech guides.
> 
> Cheers, Al


I'm doing well today then!


----------



## M4tt

> Matt - here's what you said in your initial post:
> 
> 
> 
> 
> "However the cost is that it uses energy more rapidly, this means you have to balance several other compromises. You could reduce the reserve or you can increase the strength of the spring."
> 
> 
> 
> This is not true as I've stated. Power reserve is a function of mainspring length and beat rate. Strength of the mainspring has nothing to do with it.
Click to expand...

Perhaps we are talking cross purposes, but if you really are saying that: 


> Power reserve is a function of mainspring length and beat rate.


and nothing else, then you are quite definitely wrong. Power reserve is a function of a whole load more factors. One of these is without doubt the strength of the mainspring. I can only imagine that you are misinterpreting the word strength as 'resistance to breaking'. What I mean is 'ability to contain more energy'. This is clearly disambiguated by quoting the sentences that follow the sentence that you have quoted:



> You could reduce the reserve or you can increase the strength of the spring. With around a 46 hour reserve, it is pretty clear the choice taken here. *This means that there is going to be more torque available.*


Imagine a very fine mainspring that is twenty centimetres long and a more substantial one which is twenty centimetres long. All other factors being equal, the more substantial one will be able to hold more energy than the fine one. This is what I mean by stronger and it most certainly does have something to do with it. Frankly I can only assume that you are tired and rushed this as this: 


> Power reserve is a function of mainspring length and beat rate. Strength of the mainspring has nothing to do with it.


seems an odd mistake to make and at odds with your earlier points.



> I have no idea what pretensioning is that you are referring to, and why you are saying the the entire length of the spring is not used - there is no geneva stopworks or similar mechanism in these calibers. The spring is used as much as in any watch, and the springs are the same modern shape.


My mistake, apparently.



> But I can say that torque comes from one place - the mainspring.* If the mainspring is weaker, it puts less torque into the train*.


Precisely! And if it is stronger, it puts _more torque _into it.

Either way, I don't think that this is the point really; my key point was As I said:



> your apparent conclusion, that the going train in the 7750 is actually handling less torque and is consequently less stressed than the going train in the 321 is one that is intensely surprising to me.


Have I misunderstood you or am I mistaken in this supposition?

Seriously Al, I'm pretty good with words and I trained as a mechanic as a youth, but I'm not a watchmaker. I'm describing what I understand as best as I can and I'm very happy indeed to be wrong because it means that I am correcting an error. I'm acutely aware that I am an autodidact in this area and that usually means that there will be a few major errors lurking. Right now I really don't know whether we are talking at cross purposes, if you think I am wrong in my claim about high beat and low beat watches and wear or whether you are just being a bit pedantic about the way I have said what I said rather than my conclusion.

Ultimately, my claim was that the Speedmaster would suffer far less wear in the very long term because it was under less stress as a it had a low beat movement.

Do you consider that assertion to be false?


----------



## Archer

I don't know where this conversation is going wrong, but I'll try to start from the simplest place to try to leave out things like how "stressed" the train is, because I don't really know what you mean by that term.

The amount of torque available is determined by the strength, not length, of the mainspring. So for example, at any given time "X" is amount of torque being delivered by the mainspring, and this is determined by the width and thickness of the spring cross section (note that in watchmaking terms, the "strength" refers usually to just the thickness of the spring, since you don't normally change the width). The amount of time it gives out "X" torque is determined by it's length.

If I have a watch that I want to increase the length of time it runs, I don't increase the width or thickness of the spring, but it's length. This is easily proven by installing a shorter or longer spring (of the same strength) in any watch, and seeing how long it runs. Longer spring = longer running time.

If I keep the length the same, and the width the same, but increase the thickness of the spring, then more power is delivered to the train, and this will result in increased balance amplitude. This is why Rolex makes different strength (thickness) mainsprings for example because some watches require less power, and the standard strength would lead to excessive amplitude, knocking, and a fast rate. I just had this the other day on a vintage Rolex, and had to install a weaker mainspring.

I hope this is clear so far. If it is I'll continue tomorrow, because yes I am tired.

Cheers, Al


----------



## M4tt

I suspect it is really simple, and largely my fault for using words imprecisely. It looks to me as if you picked me up on the word strengthen

If I had initally said 'increase the amount of energy held by the spring' or 'increase the output of the barrel' rather than 'strengthen the spring' I rather suspect that this whole argument would either not have happened or would have been much clearer. I wasn't really interested in *how *the amount of energy held in the spring changed, but *that *it did. Initially, I clearly used the word 'strengthen' in a technically incorrect manner. However, equally clearly the point I was making was about increased torque increasing wear. I assume that you agree that this is the case and so all that seems uncertain here now is that I read you as saying that the 7750's mainspring produces less torque, which I was extremely surprised to hear.

You may still disagree, but how about rereading what I have already written with that substitution?

I'm not around for a while now so expect a slow response to this one.

Sorry.


----------



## Archer

M4tt said:


> I suspect it is really simple, and largely my fault for using words imprecisely. It looks to me as if you picked me up on the word strengthen
> 
> If I had initally said 'increase the amount of energy held by the spring' or 'increase the output of the barrel' rather than 'strengthen the spring' I rather suspect that this whole argument would either not have happened or would have been much clearer. I wasn't really interested in *how *the amount of energy held in the spring changed, but *that *it did. Initially, I clearly used the word 'strengthen' in a technically incorrect manner. However, equally clearly the point I was making was about increased torque increasing wear. I assume that you agree that this is the case and so all that seems uncertain here now is that I read you as saying that the 7750's mainspring produces less torque, which I was extremely surprised to hear.
> 
> You may still disagree, but how about rereading what I have already written with that substitution?
> 
> I'm not around for a while now so expect a slow response to this one.
> 
> Sorry.


Hi Matt,

I know you have said you are away for a bit, but I have no doubt you will see this reply and follow up.

Indeed I picked up on the word strengthen, because that's what you said and what is misleading. if you had said to increase the length of the mainspring (or something similar) I would not disagree at all.

This theme of more torque/strength for a longer run time was repeated:

"That's fine, my point was about the output of the entire going barrel causing increased wear due to there being more torque."

"Power reserve is a function of a whole load more factors. One of these is without doubt the strength of the mainspring."

It seems you really mean the energy stored in the barrel as a whole, which is not the strength and does not affect the torque. To use a car analogy (which I admit is not the best but works for this purpose) the engine output is measured in torque, and you are saying that by adding a bigger gas (petrol) tank will create more torque and therefore more wear. Like in a car, the size of the tank is the length of the mainspring, and in both this determines running time. Torque or strength is not affected by the size of the tank, or the length of the spring.

I've already given an example of the Cal. 321 compared to the 7750, but let's look another more direct comparison. Here is a photo of two mainsprings:










The upper spring as noted is for an ETA 6497-1, which beats at 18,000 vph and has a power reserve of 46 hours by the specs. The lower spring (please excuse the fact that it is broken) is from an ETA 6497-2 from a Panerai I serviced not long ago*, and this movement beats at 21,600 vph and has a stated reserve of 56 hours. As you can see, even broken the 6497-2 mainspring is longer than the 6497-1 spring is. One measures about 21 inches and the ther 25 or so without the broken bit added in. Both movement have the same basic design/layout and the same number of jewels.

The other dimensions are also interesting, in that the width of the springs is the same, and the 6497-1 spring, which has a shorter reserve than the 6497-2 is slightly thicker/stronger than the 6497-2 spring is.

So the assertion that more torque is needed for a higher beat rate isn't true. It certainly might be the case that a watch with a higher beat rate has a stronger spring, but it can't be said that it's true across the board.

* - the most common reason a 6497 based Panerai ends up on my bench is from a broken mainspring.

Anyway, I think this should hopefully clarify my point.

Cheers, Al


----------



## JP(Canada)

Archer said:


> Personally I don't think the 7750 family gets the respect it deserves, maybe because it's so common. It's a robust movement that runs well, has great accuracy, and is very serviceable.
> 
> Hope this helps.
> 
> Cheers, Al


I love the slow beat hand winders, but that statement there is absolutely 100% how I feel about the 7750.


----------



## Kizzi

If it looks good, it is good.


----------



## M4tt

> Hi Matt,
> 
> I know you have said you are away for a bit, but I have no doubt you will see this reply and follow up.


You know me too well!



> Indeed I picked up on the word strengthen, because that's what you said and what is misleading. if you had said to increase the length of the mainspring (or something similar) I would not disagree at all.


Yes, I think I have conceded that the word 'strengthen' was the wrong one and was misleading. However now that means that we are at least a little clearer about what we are discussing.



> This theme of more torque/strength for a longer run time was repeated:
> 
> 
> 
> 
> "That's fine, my point was about the output of the entire going barrel causing increased wear due to there being more torque."
> 
> "Power reserve is a function of a whole load more factors. One of these is without doubt the strength of the mainspring."
> 
> 
> 
> It seems you really mean the energy stored in the barrel as a whole which is not the strength and does not affect the torque.
Click to expand...

Yes, that is what I was referring to. One clue was that I said:



> This means that there is going to be more torque available.


This is great, because now we are actually discussing the issue rather than my poor choice of a word.



> To use a car analogy (which I admit is not the best but works for this purpose) the engine output is measured in torque, and you are saying that by adding a bigger gas (petrol) tank will create more torque and therefore more wear. Like in a car, the size of the tank is the length of the mainspring, and in both this determines running time. Torque or strength is not affected by the size of the tank, or the length of the spring.


This is a dreadful analogy, and here is why: the difference between a larger tank and a longer spring is that the energy in the tank has to be released by combustion and doesn't put any strain on the transmission until it is ignited. Like the reserve in a quartz battery the energy in the tank can be released whenever it is required. The energy in the mainspring is exerting torque continuously and would unwind through the train if it was not held in check by the escapement. Thus the train between the spring and the escapement are under constant tension which exerts continuous lateral forces upon the pivots and so on. If you had a tank ten times larger than needed in a petrol engine it would make no difference to the transmission. If you had a spring ten times larger it would most likely tear the whole train apart.

This is directly relevant to the point I was making all along, that:



> all the components between the balance and the mainspring have to continuously cope with the lateral forces produced by the spring and kept in check by the escapement - everything is under a great deal of tension and this is a recipe for increased wear on pivots, jewels, teeth and so on.


While my central point is still the assertion that the Speedmaster's train is under less tension than the 7750. As far as I can see you appear to be asserting that this is false. It may well be, and you are the expert in this area, but either I have not understood you or you have not yet produced evidence or a convincing argument that I am wrong. As it stands, you appear to be saying that, all other factors (including beat rate) being the same:

* the strength of a spring will vary the torque but will not effect the reserve - as you said: 


> Power reserve is a function of mainspring length and beat rate. Strength of the mainspring has nothing to do with it.


This also means that:

* the length of the spring will vary the reserve, but not the torque . 
*
Is this the case? *



> I've already given an example of the Cal. 321 compared to the 7750, but let's look another more direct comparison. Here is a photo of two mainsprings:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Click this bar to view the original image of 1024x680px.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> The upper spring as noted is for an ETA 6497-1, which beats at 18,000 vph and has a power reserve of 46 hours by the specs. The lower spring (please excuse the fact that it is broken) is from an ETA 6497-2 from a Panerai I serviced not long ago*, and this movement beats at 21,600 vph and has a stated reserve of 56 hours. As you can see, even broken the 6497-2 mainspring is longer than the 6497-1 spring is. One measures about 21 inches and the ther 25 or so without the broken bit added in. Both movement have the same basic design/layout and the same number of jewels.
> 
> The other dimensions are also interesting, in that the width of the springs is the same, and the 6497-1 spring, which has a shorter reserve than the 6497-2 is slightly thicker/stronger than the 6497-2 spring is.
> 
> So the assertion that more torque is needed for a higher beat rate isn't true. It certainly might be the case that a watch with a higher beat rate has a stronger spring, but it can't be said that it's true across the board.


I'm not sure that I understand. While this is interesting, it seems to be begging the question as it assumes that only spring strength increases torque and spring length does not increase torque.* This is the thing that remains to be proven.* I concede that I caused the problem to begin with by using the word 'strength' incorrectly to mean the overall output of the whole spring in the barrel rather than how much the spring itself resisted deformation. However, now (thanks to your intervention:-!) I am using the word 'strength' correctly. However, I still think that my general point, that highbeat movements, all things being equal, generally require a mainspring which can exert more force and that this is a factor in increasing wear is correct and that my specific point: that the 861, 321 and 1861 train is under less stress than the 7750's train and that this is a factor in the Speedmaster movement's longevity.

Your counter argument: 


> Regarding the run time and what needs to happen with the spring for a faster beat rate, it's not necessarily the strength that increases, but the length. For example for the Cal. 321 the mainspring is some 13.5 inches long, where the 7750 spring is more like 23+ inches long. Strength does not enter the equation with all else being equal.
> 
> Now regarding strength, looking at mainspring sizes, the 7750 spring is a little bit wider, at 1.5 mm instead of 1.3 for the 321. Increse in strength is proprotional to the width, so this is about 15% stronger. However, the thickness of the 7750 is less than for the 321. The 321 is 0.13, where the 7750 is 0.11, and since thickess increses or decreses strength cubed, this has much more impact than width does. So if I have my numbers straight the strength of the 7750 based on thickess alone is something like 62% of the 321, so the two together would result in a spring in the 7750 that is maybe 90% or so as strong as the 321....someone needs to check my calcs but the fundamental point is that the 7750 does not need more strength, but more length.


Has the premise that the length of mainspring (when wound) will not increase the torque produced by the mainspring and that only the strength matters. I'm just not sure this is the case, first because that simply isn't how I interpret Hooke when talking about springs within their elastic limit. To be honest, I don't rate my ability as a physicist or a mathematician, don't have direct access to the appropriate equations and am too proud to ask one of my children to do the maths for me. I may well be wrong, but I'd like to be proven wrong and, at this point that means someone, yourself or Chronoscot for example, explaining the relevant equation and demonstrating that, when fully wound, length does not change the torque of a spring, because it seems to me that it will. Second this is what I have been told by people I trust repeatedly and seems to be the recieved wisdom of the WUS community (excluding Lysander, who I happily concede is both cleverer and a better physicist than I am). However, the wisdom of crowds is notoriously low and so I'm open to disproof.



> * - the most common reason a 6497 based Panerai ends up on my bench is from a broken mainspring.


For some reason I am strangely comforted by this! :-d



> Anyway, I think this should hopefully clarify my point.


I'd say so. Hopefully it will make it easier to focus on where we appear to disagree...


----------



## Archer

Okay, dragged out my watchmaking school textbook (Theory of Horology) and here is the calculation for mainspring torque in a watch barrel:










Where Mmax = torque in N.mm

e = thickness of the spring in mm

h = height of the spring in mm

σmax = acceptable maximum stress in MPa or N.mm

Length is not a factor in the calculation.

Cheers, Al


----------



## M4tt

> Okay, dragged out my watchmaking school textbook (Theory of Horology) and here is the calculation for mainspring torque in a watch barrel:
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Where Mmax = torque in N.mm
> 
> e = thickness of the spring in mm
> 
> h = height of the spring in mm
> 
> σmax = acceptable maximum stress in MPa or N.mm
> 
> Length is not a factor in the calculation.
> 
> Cheers, Al


That's really interesting. So, what are the factors that will determine the variable σmax?

As you say, σmax is measured in N.mm which is short for *Newtons per square millimeter*. Surely that means that a longer mainspring will have a higher σmax than a short mainspring for the simple reason that the longer spring will have more available square millimetres for Newtons to be applied to. As a result, if all other things were equal wouldn't σmax vary with spring length as I have been asserting? Doesn't that make length a rather important factor in the calculation?


----------



## Archer

M4tt said:


> That's really interesting. So, what are the factors that will determine the variable σmax?
> 
> As you say, σmax is measured in N.mm which is short for *Newtons per square millimeter*. Surely that means that a longer mainspring will have a higher σmax than a short mainspring for the simple reason that the longer spring will have more available square millimetres for Newtons to be applied to. As a result, if all other things were equal wouldn't σmax vary with spring length as I have been asserting? Doesn't that make length a rather important factor in the calculation?


N.mm is "Newton millimeters" not "Newtons per square mm"

Cheers, Al


----------



## M4tt

My mistake, serves me right for doing this off the top of my head, that is a bit of a schoolboy error. 

However, the question still remains: what are the factors that will determine the acceptable maximum stress of a mainspring?

Because I'm still pretty certain that one of the factors is length...


----------



## Zidane

Great info in this thread. Thanks Al & Matt.


----------



## M4tt

> Great info in this thread. Thanks Al & Matt.


Hmmm, well it appears that at least half of it is wrong, However, I'm really not sure which half! I'm a few decades from last studying this and it shows.


----------



## MH434

It has been many years since I did undergraduate physics, so I step somewhat fearfully into the ring!

I believe the torque of a spiral torsion spring is proportional to the modus of elasticity of the material, the angular deflection, the material width, the cube of the material thickness and _inversely proportional_ to the length of the material (since less bending is occurring the greater the length of the spring).

Obviously this doesn't take into the account the diameter of the barrel.

So, if correct, this would seem to throw a cat amongst the pigeons!


----------



## M4tt

> It has been many years since I did undergraduate physics, so I step somewhat fearfully into the ring!
> 
> I believe the torque of a spiral torsion spring is proportional to the modus of elasticity of the material, the angular deflection, the material width, the cube of the material thickness and _inversely proportional_ to the length of the material (since less bending is occurring the greater the length of the spring).
> 
> Obviously this doesn't take into the account the diameter of the barrel.
> 
> So, if correct, this would seem to throw a cat amongst the pigeons!


Thanks for having a go, I wouldn't be too worried. I agree that less bending is occurring, but isn't it occurring to more material? might the two not cancel out? If this is the case it would suggest that Archer is correct?


----------



## MH434

M4tt said:


> Thanks for having a go, I wouldn't be too worried. I agree that less bending is occurring, but isn't it occurring to more material might the two not cancel out? If this is the case it would suggest that Archer is correct?


For a given material and cross-section, I think it is the amount of bend that dictates the torque. The length is related to the total energy stored, but at the same time reduces the amount of bend. It is this interrelation between energy store and amount of bend (greater length increases energy storage but reduces bend) that is at the heart of the confusion. That is, if my reasoning is correct!


----------



## M4tt

> For a given material and cross-section, I think it is the amount of bend that dictates the torque. The length is related to the total energy stored, but at the same time reduces the amount of bend. It is this interrelation between energy store and amount of bend (greater length increases energy storage but reduces bend) that is at the heart of the confusion. That is, if my reasoning is correct!


Yes, I'd say that you are spot on. As is fairly clear, at this level my physics is starting to look fairly dodgy. I am quite certain that length is a factor, and that Archer is incorrect in asserting that it isn't, but frankly my applied maths isn't up to working out what the effect of length is. As you have a degree in it (and probably a technical calculator!) and I don't, perhaps you could struggle your way through the application of Young's modulus to this problem.

Personally having slept on it, my intuition is that the amount of bend will not be reduced by so very much by extra length when the spring is wound in situ, and that the extra force exerted by the spring as the coils move further from the core of the mainspring is a variable we haven't considered. However, determining σmax, the maximum stress of a mainspring, is a complex equation that definitely involves length - but which complex application of Young's modulus and a bunch of other variables describes this complexity isn't at all clear to me. More to the point, it seems to me that the limiting factor in a barrel with a core isn't the point at which permanent deformation happens, but the point at which the spring interferes with itself and this will be a function of both spring length and thickness as well as core and barrel diameter. An ideal spring would deform elastically until it deformed inelastically while a mainspring deforms until the spiral is too tight to allow further deformation qua spring.

In short I now feel absolutely certain that Archer is definitely wrong that spring length is not a relevant variable in determining torque, but it isn't at all clear whether it cancels itself out, reduces torque or increases torque, so he may be right that it is a difference that makes no difference and can thus be ignored. I know what my intuition is, but it looks as if there is going to be a very complex equation involving quite a few variables that will define what the maximum stress of a mainspring can be. I don't have it, I can't find it anywhere and my physics (and maths) isn't good enough to derive it.


----------



## Archer

MH434 said:


> It has been many years since I did undergraduate physics, so I step somewhat fearfully into the ring!
> 
> I believe the torque of a spiral torsion spring is proportional to the modus of elasticity of the material, the angular deflection, the material width, the cube of the material thickness and _inversely proportional_ to the length of the material (since less bending is occurring the greater the length of the spring).
> 
> Obviously this doesn't take into the account the diameter of the barrel.
> 
> So, if correct, this would seem to throw a cat amongst the pigeons!


Thanks for jumping into this thread - with your entry I'll make my exit. I simply don't have time to carry on with this one - watches are waiting to be fixed and I can't work more than my current 7 days a week, so unfortunately I will bow out. Also the last time I applied "physics in anger" was probably 1985 or so in third year engineering, so not sure if yours is more up to date than mine is.

With regards to the barrel size, good that you mentioned it. Barrel diameter and arbor diameter have a direct relationship to mainspring length.

I won't say what that does to the cat, as I'm more of a dog person. 

Have fun.

Cheers, Al


----------



## Runitout

This is a quite brilliant thread. I'm learning a lot here - thank you!

Durability means a lot to me, as a watch owner: the relative merits of these movements is of more than academic interest.

Thanks again to all.


----------



## joe band

M4tt said:


> If you had a tank ten times larger than needed in a petrol engine it would make no difference to the transmission.


i feel like a minnow jumping into a pool of sharks, (though learning a lot from the discourse) but i'd like to add that a tank ten times larger would certainly effect the transmission from all the extra weight. though gas weighs less than water, it still is bit over 6 lbs/gal (sorry to use american measurements) which puts greater strain on the transmission.

the extra poundage would bring down mpg, another sign of greater strain.


----------



## exomoons

The equation to determine the correct length:

L= pi*(D*D - d*d)/2T

where:
D = Inside diameter of the barrel
d = Diameter of the arbor
T = Thickness of the mainspring
L = Length

The the strength of the spring is proportional to the cube of thickness so if you double the thickness the spring will be 8 times stronger. The width is directly proportional to the strength so if you double the width the spring will be twice as strong. The length however when cut in half will deliver twice the power so the strength is inversely proportional to the length of the spring. Having said that we can see that everything is related to one another. 

Hope that helps and hope that my reasons are correct.


----------



## M4tt

> i feel like a minnow jumping into a pool of sharks, (though learning a lot from the discourse) but i'd like to add that a tank ten times larger would certainly effect the transmission from all the extra weight. though gas weighs less than water, it still is bit over 6 lbs/gal (sorry to use american measurements) which puts greater strain on the transmission.
> 
> the extra poundage would bring down mpg, another sign of greater strain.


Yes, you are of course absolutely correct and I confess that I hadn't even thought of that, but I'm not sure it is relevant: the question was about the effect of having all of the extra energy waiting there to be used and my point was that a spring exerts the force* all of the time* while the petrol has to be burned to convert the energy into a form that will cause any strain at all to the transmission.



> The equation to determine the correct length:
> 
> L= pi*(D*D - d*d)/2T
> 
> where:
> D = Inside diameter of the barrel
> d = Diameter of the arbor
> T = Thickness of the mainspring
> L = Length
> 
> The the strength of the spring is proportional to the cube of thickness so if you double the thickness the spring will be 8 times stronger. The width is directly proportional to the strength so if you double the width the spring will be twice as strong. The length however when cut in half *will deliver twice the power *so the strength is inversely proportional to the length of the spring. Having said that we can see that everything is related to one another.
> 
> Hope that helps and hope that my reasons are correct.


I'm sure that it is right as far as it goes, however, I'm unclear how you moved from the strength of the spring to the power output. I'm sure you would agree that you haven't included the effect of winding the spring. and no one has included that effect of *gearing *yet... It seems obvious that you will be able to wind more energy into a longer spring (all other things being equal) We are all agreed that this will increase reserve (all other things being equal). The dispute is whether this will also increase (or decrease!) the torque significantly


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## ramboooo

Sometime the value is more on historical value and originality


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## exomoons

My bad they should both be torque.

As for the whether the longer spring provides more torque or not let's look at the following equation:

M = pi*E*b*t*Ө / 6L

Where:
E= Modulus of elasticity (MPa)
Ө= Angular deflection in revolutions
L= Length of active material (mm)
M=Moment or torque (N.mm)
b=Material width (mm)
t=Material thickness (mm)

We can see that if L increases then M decreases&#8230;now the conclusion is yours.


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## M4tt

> My bad they should both be torque.
> 
> As for the whether the longer spring provides more torque or not let's look at the following equation:
> 
> M = pi*E*b*t*Ө / 6L
> 
> Where:
> E= Modulus of elasticity (MPa)
> Ө= Angular deflection in revolutions
> L= Length of active material (mm)
> M=Moment or torque (N.mm)
> b=Material width (mm)
> t=Material thickness (mm)
> 
> We can see that if L increases then M decreases&#8230;now the conclusion is yours.


I see the point, and I agree that, _for an equal number of revolutions_ this would be correct, but my intuition is that, all things being equal, (apart from the size of the barrel perhaps - which has implications for torque). a longer mainspring would be capable of more revolutions, thus increasing the overall angular deflection. You appear to assume that both springs are capable of being wound the same number of revolutions and I don't think that this is the case; to be able to solve the equation you also need to know what σmax (or the point at which the spring begins to interfere with its own operation) are for each spring.

However, this is definitely moving us forward in a terribly complex terrain, thanks.


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## geome

pgrivas said:


> I am new to watch collecting and just picked up a brand new sapphire sandwich Speedy. Unfortunately it's running about 25 seconds fast per day.  I've read to maybe wait a month before having it serviced. Does that seem like the right thing to do?


I purchased one mine was the the same running about 20secs fast per day
Now after wearing the watch for approx 1 month it has settled down to + 2secs a day


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## georges zaslavsky

the lemania 2310 withstood many tests that other handwound column wheel chrono movements like the rolex 727, the longines 30ch or the excelsior park calibre that was found in the doxa chronograph haven't passed.It is still used by breguet and vacheron. The lemania 1350 is used by breguet and ebel


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## Psychos

Just found this wonderful thread, definitely a fascinating reading, thank you M4tt and Al!

Al, from your posts I had an impression that from the technical perspective you don't regard Lemania 1873 as anything special compared to Valjoux 7750, is this correct?

So coming back to the OP question, could Lemania 1873 have most of the fame only thanks to the historical significance or is it somehow technically superior to other movements in its price range?


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## Zarath

I second Psychos' remark. I came to this thread hoping that I would get some evaluative information on the Speedmaster Pro movement, but instead there's five pages of physics... 

I'm thinking about buying a Speedy Pro, but the only thing that's holding me back is the fact that it's a lot of money for a pretty old (and outdated?) movement. Especially when that movement is not quite special compared to others in the same price range. Or is it?


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## Psychos

Zarath said:


> I'm thinking about buying a Speedy Pro, but the only thing that's holding me back is the fact that it's a lot of money for a pretty old (and outdated?) movement. Especially when that movement is not quite special compared to others in the same price range. Or is it?


I was asking myself exactly the same question some time ago  However now I am 100% sure that I will buy Speedy Pro because it stood the test of time and is as beautiful and reliable as it was 50 years ago. Other watches will come and go, but Speedy Pro was, is and always will be special.

From the technical perspective it may not have the most modern movement, but you can be sure that it will last a very long time with proper servicing.

However an expert's opinion on the Lemania 1873 vs modern chrono movements would be very welcome.


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## Camguy

Absolutely fascinating and informative thread...I'm going to go take a couple of aspirin now. ;-)


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## Psychos

Related to the OP question I found this interessting opinion: Don Aldo on the Speedmaster Professional and the myth of 'toughness' - The Military Watch Resource - Community Fora


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## Zarath

Psychos said:


> Related to the OP question I found this interessting opinion: Don Aldo on the Speedmaster Professional and the myth of 'toughness' - The Military Watch Resource - Community Fora


That's a good find! Thanks.


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## Camguy

I can jump back in here with some actual experience with the 1861. I recently picked up a 2007 3750.50 , and it's lost about four seconds in a week, worn 24/7.


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