C4.4.3 The Chronograph Train

You will find that some mechanisms will record 10ths of seconds or even provide a split seconds function, but the most common types of chronographs will simply provide recording of seconds and minutes, and you may also find that certain calibers will record hours as well.

Further to this, it should be noted that some chronograph calibers will have different revisions and record, perhaps, 30 or 45 minutes depending on those revisions.

For now we will discuss the recording of seconds and minutes and in a separate lesson we shall take a look at how hour recording is achieved.

We have discussed how driving force is delivered to the chronograph mechanism, now lets take a closer look at the chronograph train of wheels and how they interact together.

So to recap, the Driving Wheel is turning all the time along with it’s host wheel and this is geared with an intermediate wheel mounted to the Coupling Clutch.

When the user engages the chronograph, the coupling clutch shifts it’s position so as to cause the Intermediate Wheel to gear simultaneously with the Driving Wheel and the next wheel in the chronograph train, typically being the Chronograph Runner Wheel.

The Chronograph Runner Wheel turns once in every 60 seconds and the main Chronograph seconds hand will be fitted directly to it’s extended pivot.

The Chronograph Runner Wheel has an extended finger which interacts with the next wheel in the train, and this is called the sliding gear. It will nudge over the sliding gear once for every full rotation of the Chronograph Runner, I.e. one time every 60 seconds.

The Sliding Gear is interfaced with the next wheel in the train and this is called the Minute Recording Runner. The Minute Recording Runner will also have an extended pivot to which the minute recording hand is fitted.

There is a spring which acts against the teeth of the Minute Recording Runner and causes it jump in intervals rather than turn smoothly, one interval being representative of one minute.

The gearing ratio between the Sliding Gear and the Minute Recording Runner will determine how many intervals, or minutes, will occur per full rotation the Minute Runner,  and this will typically be 30 or 45 minutes, but it really does depend on how the particular movement was designed. Either way, the principle stays the same.