Jaeger-LeCoultre

hi folks,

i was talking watches to my son this afternoon. i showed him my Reverso Grande GMT and told him that this watch has 8 days power-reserve because it has 2-barrels running inside.

then, he asked how do these 2 barrels run? they both run independently? and how subsequently the energy be stored in the watch?

i responded to him that these are very good questions, i do not have very clear answers either, it would be interesting to post these questions to fellows in this JLC forum. You guys probably have the answers in mind or may be able to provide further pointers to me.

by the way, some pictorial answers would be much helpful so that i can show and explain it to my son who is 14 years old only.

thanks in advance!

stefan

indicate and inquisitive and strong thought process for his age.  I wish I could help but I am clueless too.

hi Arthur, my son read your reply, he smiled and said "thank you for your kind compliment."

stefan

Hi Stefan, hi Stefan's son!

I know of three different reasons to put two barrels into a watch:

1. You need a lot of torque for driving something big. 
   

Hi Stefan, hi Stefan's son!

D..., I always mix up the "Insert" button and the "Igame uploader" link.............. Sorry for the first post.
So here we go again:

Basically I know of three reasons to put two (or more) barrels into a watch:

1. You want to drive different things in the watch independently like in a DuoMètre, a Minute repeater or something similar.

In this case the crown wheel (red) would drive the click wheels (blue) together or independently (like in a DuoMètre, where turning the crown in one direction winds one barrel and turning it in the other direction winds the other) and thus wind the barrels (orange). Both barrels would then run independently turning their loads (green)


2. You want a lot of torque for driving something big.

In this case the crown wheel would turn both click wheels in parallel winding both barrels at the same time. The two barrels then operate in parallel, joining their torque to drive the load (green) together. This will increase the torque, not the power reserve as both barrels are operating all the time at the full speed required by the load. It is comparable to operating two batteries in parallel.


3. You want a long power reserve (as in your Reverso Grande GMT)

In this case the crown wheel operates on the left click wheel only. As soon as the main spring in left barrel is wound tighter than the one in the right barrel, the barrel will start to turn in the same direction as the click wheel. So in this moment the left click wheel/barrel combination starts behaving a little like a single gear wheel. (We are still winding the watch.) Because the left barrel it is connected with the right click wheel by an intermediate gear the red crown wheel is now driving the right click wheel (blue) also and thereby winding the second barrel (orange).

During normal watch operation the right barrel will have the task of driving the load (green). The left barrel assumes the task of turning the click wheel of the right barrel and thereby helping to drive to right barrel. Sounds funny? Let's assume that both barrels have the same specifications: Then the rotation of the right barrel will be driven in equal parts by two sources:

• The left barrel drives the right click wheel through the intermediate gear.
• The main spring within the right barrel turns the barrel agains the right click wheel.

Because the right click wheel is already turning (driven by the left barrel) the speed (not the torque) of the two rotations will sum up and drive the load (green) together. So what we have here is two barrels unwinding at only have the normal speed and therefore more or less adding their power reserves.
There are many variations to this scheme in reality. Barrels of different specifications are combined with intermediate gears that implement transmission rations other than 1:1. Reasons for this are many and too complex for me to grab. It is something about dealing with the fact that main springs have a non linear torque profile.
A more space economic way to implement the serial double barrel scheme is to leave out the intermediate gear and turn the right barrel upside down. But the principle remains the same;


I hope I could give your son an idea of what is happening inside your great GMT. And please excuse the poor quality of my quick drawings.

Best,
Martin

This message has been edited by stromer on 2010-01-17 02:15:20

this is why I like this forum!

It would be great if "technical" posts like this could be grouped into a sticky thread or a wiki area for future reference - or is there one already?

stitch

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for such a detailed explanation....



Cheers

three barrel watches work the same way?

Cheers

go by the same principles as a set of two.

However combinations of the things said about two barrels could theoretically be used with three or more.
However I do not know about any example where this was done in reality. If anybody does I would be glad to happy about it.

Best, my friend
Martin

I hope, my friend, that you are enjoying your Sunday.....

Cheers

but I am enjoying my spare time with indoor acvities nevertheless. I hope you do also. If it gets too bad outside you can still listen to your ding-ding-thing ;-)

Best, Martin

I just finished my run outside....

rain, cold and I enjoyed it.....

Now I am going to relax....if my kids let me do so ...

Cheers

I had the feeling you have something you haven t revealed yet........Or Have I  missed something lately???Too many clues...does it ring???PM if you want...Yours,Mo.

There is something.... and a photo was posted but at the end of a long thread......

As you understood... there are clues....

I am preparing a post.....

Cheers

ps pm sent

for this clear explanation.Sometimes we talk a lot about things we know little about.This is the beauty of sharing.Yours,Mo.

hi Martin,

thank you so much indeed for the excellent note with very self-explanatory drawings.

since i have posted the questions to this forum, my son asked me any people responded to our post so far. you know we have been waiting for such well-written answers!

after receiving your post, my son and i both were sitting together in front the computer to understand what are the differences of these three combinations of two barrels. we talked and discussed, and talked and discussed again, finally understood all of your answers well. the most happy thing to me he can understand what you are talking about much faster than mine. when I don't understand some of the details, he tried to explain it to me. apart from understanding how the two barrels are running inside the GMT, now both of us are so happy to learn thing together which help us strengthen our bonding.

by the way, we love your drawings which indeed helped.

thanks once again, Martin!

stefan

PS: after understanding how two barrels run inside the GMT, have one more question in mind, hope you or other guys can provide hints for this - this GMT has 8 day power-reserve, however comparing with other watches that has only barrel inside, the number of turns of winding the crown to full power for this GMT seems much lesser. is it because of this 2-barrel design? (my question is clear to you!)

Our passion sometimes can be a lonesome one (that's why we meet in this forum, right?) and so I like it very much if someone not deep into watches is asking questions. We cannot leave them alone with their questions.
In this case your son asked and I am very happy to have helped you to share some intense moments with your son

As for your last question:
The power reserve of a watch is determined by the (average) force that the mainspring transfers to the barrel rim, the number of rotations the main spring can drive the barrel and the number of main springs.

Physically spoken it is expressed as:   Work (W)=Force (F) x distance (d) x n
where W is the work performed by the barrel(s) when it(they) drive(s) the movement for x days, F the force of each main spring, d the number of barrel rotations and n the number of barrels,

You can play around with the barrel diameter in order to increase F but that will at the same time decrease d so that the available work (the power reserve) will remain basically the same. It is obvious that adding another barrel (i.e. increasing n) to a present one will increase W.
However you could replace one barrel containing a strong main spring with two barrels containing weak springs and still receive a similar power reserve like before (in this case you would be lowering F and increasing n)

When you wind the watch you put into the barrels the energy needed to perform the work W .
Here the same Physics applies: Work(W)=Force'(F') x distance(d')
But here F' is the force you need to apply to the crown stem and d' is the number of crown rotations. The number of barrels does not appear here.

You will have to achieve this work W by turning the crown. You can have many soft  rotations of the crown or you can have fewer but tighter ones to achieve the same work (i.e. power reserve). The watch maker designing a movement can play around with the transmission ratio of the winding train and thereby change the ration between F' and d'. But in the end their product will have to remain the same in order to achieve a certain W. That's Physics. It cannot be cheated.

So I would assume that if your Reverso GMT requires fewer rotations of the crown to wind it than other watches with the same power reserve, then you need a firmer grip on its crown than on the others. This does in theory not depend on the number of barrels. (In reality there may be other mechanical effects that do not know about and did therefore not consider.)

I am quite sure that the last thing your son was asking for was a Physics sermon. And even no pictures this time! However the functional part of watchmaking is Mechanics and Mechanics is Physics ;-)

Have a great evening and enjoy the rest of your weekend!
Best,
Martin
This message has been edited by stromer on 2010-01-17 08:53:00

Thanks for the continued explanation. I was going to ask what the relationship was between a barrel and a spring, but I think you have answered it. Is it correct that each barrel contains its own spring, thus is an individual reserve of power?

--Sancerre

No message body

Martin, thanks very much for the detailed reply. my son just started learning physics subject in his school, he is interested in your reply. he needs to take some time for him to digest this a bit more. he won't answer more question for now.

in any case, understand this technicality more which lets us appreciate our watches more too. so that we will think what is happening behind the dials.

stefan

I think a link to this post should be placed on HoMe for the general benefit of those of us not so fully conversant with the mechanics of our beloved watches.

Thanks

Nikolaj

Much appreciated, my friend.

As per Nikolaj's suggestion, I will save your post in our new blog post, if you don't mind.

Best, Martin.

Nicolas

No message body

I love your explanation and drawings.  Your post was very informative.  I appreciate all the time you took in creating these examples for all of us to enjoy.

Cheers,

Daos

so much from most of you that I gladly grab my chances to give back as much as I can.

If I only had more oppertunities to meet you gals and guys in person!

 

Best,

Martin

Very nice of you to explain it so clearly! Last week I was searching for some material on caliber 878. Although there is not much available I found the following illustration. It shows very nicely how the barrels are placed and connected.

 

 

During the Masterclass we worked on the caliber 875 of the Reverse Grande Date. It has the same setup with the barrels. Very nice to see how these work together.

If you join LeClub you can play the watchmaking game. With some help you can assemble the 875 caliber. It illustrates very nicely how the watch works.

Greets! Rik

This message has been edited by rik1 on 2010-01-17 22:55:44

i didn't know we can play watchmaking game in LeClub. should try it out soon.

thanks,

stefan