Jaeger-LeCoultre

Two weeks have passed now since we were placed in front of the new chronograph from Jaeger-LeCoultre, the Duometre a Chronographe

You may imagine and understand that this new watch, first piece of a promising collection, has encountered a huge success at the Geneva show and probably everywhere where visible.

The idea of a double barrel, each one of the two being linked to its own wheel train, one for the time, the other for the chronograph, is a chosen way to avoid any interference of the chronograph activation on the precision of the watch.

The Duometre calibre 380

The absence of any clutch is another way of avoiding interference. Starting the chronograph is quite often seen as a source of interference and tear.

Let's get this movement stripped off

So on this watch the chronograph wheel train is directly linked to the escapement without clutch. This very escapement is also used by the time wheel train.

Did you wonder how you can stop one of the two wheel trains without stopping the other, while they are regulated by the very same escape wheel when there is no clutch?

A glamorous press kit picture to locate our subject

Here is the first secret. Let's have a look around the lightning second wheel. Indeed the lightning second wheel is directly engaged on the escape wheel. It is the first wheel in the wheel train from the escapement.

The lightning second bridge

Let's get this lightning second bridge off and see under how it looks. You see the lightning second wheel with its 6 teeth, right between the column wheel and the balance wheel.

The lightning second wheel between balance and column wheel

This lightning second wheel is in fact made of 2 similar wheels, one on top of the other. They have the same axis. One (the top one) is fixed on the axis without any play. The second one has a half tooth play with the fixed one. The fixed one is engaged on the chronograph wheel train. When the chronograph is stopped, this one is obviously stopped. The other one is engaged with the escape wheel.

The lightning second wheel from top

Everything happens between the two wheels with this little half tooth play. The "free" wheel engaged with the escapement has a little hole. This hole receives a pin fixed on the fixed wheel. When the fixed wheel is stopped (chronograph stopped), its pin allows the "free" wheel to move on its half tooth play, going from one extremety of the hole to the other. This limited play allows the escape wheel to "find its way" without blocking at the lightning second wheel.

Lateral view of the lightning second wheel

When the chronograph is activated, the chronograph barrel pushes on the chronograph wheel train up to the lightning second wheel and the escapement. The fixed wheel (with the pin) pushes on the "free" wheel (the pin always resting on one extremity of the hole) so that this one cannot play between the fixed one power and the escape wheel impulsion.

Clever no?

The column wheel

Here is another secret of the Duometre a Chronographe, more important for users we intend to be someday (let's hope).

It is a column wheel activated chronograph. In the drawing below the chronograph is activated. The lever between the column wheel and the lightning second wheel falls inside the column wheel, liberating the lightning second wheel.

The chronograph is started

On the drawing below the chronograph is stopped. The lightning second is stopped and the lever is in the opposite position, fully out of the column wheel.

The chronograph is stopped

You can also see it on the picture below. Please note that the picture is taken on a partly dismantled movement and the lever is at the right position for a stopped chrono but the column wheel is obviously not in the right position. One extremity of the lever is out of the column wheel, the other extremity is inside the lightning second wheel, stopping it.

Picture of the lever when chrono is stopped

The last situation is resetting. When the chrono pusher is pushed for resetting (please note pushed and kept pushed to that point), the lever is placed on the colum wheel in an intermediate position. It is clearly visible in the drawing and the picture below. At this position the lever is partially disengaged of the lightning second wheel and so the chronograph wheel train is liberated.

Zero reset of the chronograph

You may find it strange and that's indeed unique. In the resetting position the lightning second wheel is liberated but only so that it turns to go back to the zero position. It makes consequently at maximum between one sixth and five sixths of a turn. Once again the pusher must be kept pushed. The lightning second wheel is only partially liberated because the lever is only partially liberated. In this intermediate position it still engages with one of the six teeth of the lightning second wheel (a thicker one). When the lever encounters this thicker tooth, the lightning second wheel is stopped again, in the zero position.

Zero reset of the chronograph pictured

I've asked you to keep the chrono pusher pushed. Now that the lightning second wheel has been liberated enough to go back to the zero position, you can release the pusher. When the pusher is released, the hammers for resetting the chrono wheels through their hearts are released and can push on the hearts and reset the full chrono.

That means that if the chrono pusher is immediately released when pushed, the lightning second may not be brought back to zero (but other indications are). The lightning second hand can't be controlled by a traditional heart as it is too thin and would be broken by a hammer force.

So please when you get your Duometre a Chronographe and try it, please don't say that the lightning second hand is not aligned! Give it a chance to go back to zero! 

I hope you enjoyed this little explanation. I love this watch!

Dje