Chronograph Functions in Detail

As defined previously, a chronograph is a watch that tells the time and records elapsed time on demand.

It’s basically a watch with a stopwatch attached to it. To make such a thing possible, a lot of parts, specially tailored to keep friction to a minimum, are necessary.

I know I keep banging on about friction, but it really is the main problem horologists must overcome if their produce is going to function as well as it must to maintain the reputation of our industry.

We all understand that friction is a big enough problem in a regular watch. In a chronograph, it is out of this world. Imagine bolting a second unit, full of teeth, leaves and springs, onto a watch and expecting it to drive itself and the additional unit. It is asking a lot, and if we as watchmakers expect that poor little mechanism to perform, the least we can do is ease its burden as much as possible.

So, familiarise yourself with the following parts. They are commonly found in a chronograph. Explanations of those parts which are not self-explanatory will follow, but for now, know that when you see any of the below, we’re talking chronographs.

The parts of a chronograph:

1. Intermediate Chronograph Lever Spring
2. Eccentric for Chronograph Lever
3. Drive Wheel
4. Clutch wheel
5. Heart Cam for Seconds
6. Chronograph Wheel (centre)
7. Minute Jumper Spring
8. Minute Counter Jumper
9. Heart Cam for Minutes
10. Zero Pusher Piece
11. Rocking Lever Spring
12. Hammers
13. Brake Lever
14. Brake Lever Spring
15. Main operating Lever
16. Rocking Lever
17. Lower Cam
18. Intermediate Operating Lever
19. Upper Cam
20. Zero hammer Spring
21. Eccentric stop pin for Intermediate Chronograph Bridge
22. Cam Jumper Spring
23. Minute Counter Wheel
24. Intermediate Minute Counter Wheel

Most every chronograph will have a seconds register. Of that, you can be relatively sure. The next surest inclusion on the dial of a chronograph, will be a minutes register. After that you’d expect to find an hour counter (we’ll get to the operation of those shortly), but sometimes they are replaced with something else or omitted completely.

But for now let’s just concern ourselves with the parts and operations of those parts that you will expect to find in the minute counter of a chronograph.

There are 7 main components to remember:

Chronograph wheel finger
Intermediate minute counter wheel
Minute counter wheel with Heart Cam and Minute counter hand (dial side)
Minute counter jumper
Minute counter jumper spring
Chronograph Bridge (and screw)
Chronograph Zero Hammers

The chronograph finger, which is mounted on the chronograph wheel, advances the intermediate minute wheel one tooth at a time, every revolution of the second hand, which in turn advances the minute counting wheel once a minute.

Normally the minute counter had 30 teeth and a hand to display the passing minute on the dial, which is held in position by the minute jumper and minute jumper spring, which applies the appropriate tension to ensure that the minute counter wheel advances only one minute each time. The chronograph bridge carries the bearings for the seconds and minute counting wheel. The zero hammers, in conjunction with the heart cam, return the counting hand to zero.

As well as the standard minute counter, which creeps into its new position over the last few seconds of the preceding minute, such a thing known as an Instantaneous Minute Counter exists.

Quite simply, the Instantaneous Minute Counter is a slightly more complex system that enables the minute hand to jump INSTANTANEOUSLY when the second hand ticks past 12. This is opposed to rolling counters that are geared up to creep constantly and the more common system that sees the minute hand move slightly before the second hand reaches 12 (these use a finger on the chronograph wheel, as you would ifnd in a standard ETA 861 calibre).

In place of the finger on the chronograph wheel is a snail on which rests a lever under the influence of a spring. Attached to the lever is a pawl or click.

The minute counting wheel has ratchet shaped teeth and is positioned by a conventional jumper.

The lever with the pawl is lifted by the snail and the click gathers one tooth on the minute recording wheel.

As the lever reaches the high point of the snail and falls to the lower part of the lever and pawl advances the minute counting wheel instantaneously.

Just like any good relationship, the proper functioning of any good chronograph is reliant on minimal friction and just the right amount of tension in all the right places.

Here are a couple of things to check for in regards to tension:

If insufficient tension is created in the friction spring, the second hand will judder when the chronograph is started due to the backlash in the teeth of the wheels.

If the amplitude of a chronograph falls drastically at each jump of the minute register, you should check the tension of the jumper spring for the minute counter.

If a chronograph mechanism is activated and the amplitude falls drastically, you should check the depth of the clutch wheel teeth and the chronograph wheel to ensure they mesh correctly (50% depth), and the tension of the chronograph wheel friction spring to ensure it is not pressing the chronograph wheel into the jewel.

Here’s another potential problem to watch out for:

If the minute counter of a Chronograph jumps 2 steps each time the second hand passes the 12 o’clock position, you need to check the depth of the penetration of the finger of the chronograph centre wheel and the intermediate counter wheel AND the position of the minute counter jumper.

The hour counter records timed hours (normally 12) and is usually driven from the barrel via a gear and friction device, the recording is stopped and started via a switch (the hour counter operating lever) that passes through the movement to connect with the chronograph column wheel. The hour recorder is zeroed by a separate hammer, which operates at the same time as the chronograph hammers.

Here is a list of the parts you can expect to find in a standard hour counter mechanism:

1. Hour counter operating lever
2. Intermediate hour counter operating lever
3. Hour counting brake lever
4. Hour counting brake spring
5. Pinion attached to barrel via friction spring
6. Hour counting wheel
7. Hour counting indicator hand
8. Hour counting heart cam
9. Hour counting zero hammers
10. Hour counter hammer spring
11. Hour counter bridge

The above eleven components can be said to ‘interact’ with the Hour Counter.

Everything in horology, much as it is in life, is bound by a simple equation: C:E.

That’s Cause and Effect, people. Never forget that. An action creates a reaction. In watchmaking, any movement of any piece will effect the operation of the watch. When it comes to the starting and stopping of the hour counter mechanism in a chronograph, it is most certainly the case. Please read the following carefully and slowly. Have a labelled diagram of a standard chronograph in front of you. Look at all the parts. Visualise their movement. Visualise the point at which they make contact with other parts. Get inside the watch.

Feel the action. Be part of the reaction.

Take a deep breath…

GO!

When the start/stop pusher is depressed, the main operating lever slides along the plate and, by way of the intermediate operating lever (held in place by the rocking lever and the rocking lever spring), engages with the lower level of the cam/column wheel, which clicks into a new position. The hour counting operating lever/yoke has a pin that extends through the plate to the dial side. When the hour counting operating lever/yoke is moved by the cam/column wheel, this pin engages with the switch on the dial side, which lifts the hour brake lever away from the hour counting wheel, which is driven directly by the drive pinion on the barrel. Thus, the hour counting mechanism begins operation.

The stop command works in much the same way, except the intermediate operating lever makes contact with a different part of the lower level cam, which allows the Cam Jumper Spring and hour counting operating lever/yoke to return to their original positions. Thus the hour counting operating lever/yoke disengages the switch from the hour counter wheel brake and the brake, given tension by the hour counter brake spring, snaps back into place and stops the chronograph.

Posted in tech stuff | Tagged as: , | Leave a comment

Leave a Reply

Your email address will not be published. Required fields are marked *