C4.4.2 Driving The Chronograph

And so let’s discuss how these requirements are usually achieved, and we shall start by taking a look at how a chronograph mechanism is driven. 

Simply put, the chronograph mechanism is designed with its own train of gears and we will discuss this shortly. 

The regular train of wheels within the movement is responsible for the task of driving the chronograph train. And it does this in a very similar manner as to how the train of wheels is configured to drive the Motion Works.

As you should know by now, the Motion Works are driven by one of the train wheel gears, usually the centre wheel, which typically has an extended arbor, and the cannon pinion is friction fitted to this arbor. And this drives the minute wheel which, in turn, drives the hour wheel. It’s a simple and effective way of providing an indication of elapsed time to the user.

The chronograph mechanism  is usually driven in a similar manner. One of the gears in the train of wheels, typically the fourth wheel, will also have an extended pivot, and this pivot will have a chronograph Driving Wheel fitted to it, which in turn drives the chronograph train.

The Driving Wheel attached to the extended pivot will be turning all of the time along with it’s host gear as the watch runs down. But the chronograph train only needs to be running when the user engages the mechanism.

For this reason there is a component installed between the Driving Wheel and the chronograph train and this is called a Coupling Clutch, and this coupling clutch has an intermediate wheel mounted to it. 

The Coupling Clutch wheel will be engaged with the Driving wheel all of the time, but when the user engages the chronograph, the clutch will be caused to shift position so that the intermediate wheel also interfaces, and starts driving the chronograph train of wheels.

And so let us now take a closer look at the chronograph train of wheels.