Jaeger-LeCoultre

stromer
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Winding multiple barrels

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