A. Lange & Söhne

I forgot about the balance wheel stop feature. In that case, it is entirely possible that the gear ratio of the barrel and second wheel between the old and new movements are identical, since the brake lever will stop the balance wheel before the barrel depletes. I do not have further info of the original movement to make a direct comparison - whether it also uses the brake lever or just further depletes, as your photo shows that the newer barrel's central arbor does five turns (and not completing the 6th turn) before fully unwinding to Ab. 

 

In spirit, that's actually the intention of a stopwork mechanism - it is not to stop the movement when the barrel is empty, but rather, it limits overwinding as mainsprings will have a sharp torque increase when near fully wound, resulting in too much power going into the movement's going train.

 

You accurately noted the oversimplification I made in my writeup - the central cam does indeed rotate, albeit slowly. I omitted that fact to simplify the explanation, as during winding, the central cam can be more or less be considered stationary. This is because it is tied to the arbor of the mainspring, which unwinds as the watch ticks. In other words, it is a continuous game of catching up - you're continuously winding the barrel cover clockwise to wind the spring over the watch's lifetime, while it continuously unwinds clockwise via the central arbor. The cam mechanism of the stopwork simply acts as a "limiter" to the "relative angular difference" in number of turns between the barrel and arbor.

 

The configuration of winding the barrel is a little different than a conventional wristwatch - normally, you wind the mainspring via the central arbor, and it is the outer barrel rotates to drive the movement. In the Zeitwerk, you're winding the mainspring via it's periphery, while the barrel powers the movement via it's central arbor, driving a wheel underneath. In retrospect, this is not the most space efficient solution (though the stopwork does look cool), and thus is one of the optimisations in the newer Zeitwerk Date - using the relatively conventional method of winding via the central arbor, but stacking two barrels in series for a longer power reserve.

 

As an interesting aside, since the Zeitwerk has a remontoir, you can see the central cam visibly rotate clockwise a slight notch everytime the discs jump. That is how little the barrel needs to unwind, to recharge the remontoir with a full one minute of power. Meanwhile, a regular watch without a remontoir will have the barrel continuously rotating...

 

Regards,

skyeriding

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