Explanation of the operation and structure of a mechanical hand-wound chronograph

Click here to see the movement and structure of a mechanical hand-wound chronograph in a video.

Explanation of the structure of a mechanical hand-wound chronograph


This is Seno from Vintage Watch Life.

Chronograph watches are cool, and are probably as popular a category as divers' watches.

However, because of its complexity, I think there are few people who understand why so many different needles are moving.

When I first started studying chronographs, I read and studied many reference books many times, but I still couldn't understand anything, so I thought it was okay if I didn't know anything about them anymore.

That's how I felt.

However, the more I tried to learn more about watches, the more I realized this was something I could not avoid.

I've looked into the reasons why this is so difficult, and I think there are two reasons.

The first is that even when it was explained in words, I couldn't understand it because I didn't know how it worked.

The second problem was that I couldn't understand the chronograph's movements right away.

I believe that is the case.

So, today we will be looking at how a chronograph, which seems to be quite complicated, works.

I will explain this in a way that is extremely easy to understand, so please stay with me until the end.

So let's get started right away.

Understanding the structure of a three-hand watch

Trying to suddenly understand how a chronograph works is like trying to do multiplication and division without knowing addition and subtraction.

First, understand the basic workings of a three-hand watch and then see how it connects to a chronograph.

First, let me briefly explain how a three-hand watch works.

Mechanism and structure of the barrel (first wheel)

First, by turning the crown, the spring inside the barrel is wound, and the force of the spring unwinding is used to set the first wheel in motion.

Anatomy of a Three-Hand Watch

The power is transmitted to the second to fourth wheels, slowed down using the size of the gears, and then from the escape wheel to the balance, causing the watch to start running.

To give a rough explanation, the structure of the watch is as follows.

Position of the fourth wheel on a wristwatch, seen from the front and back

And since watches that use a small second are designed so that the fourth wheel rotates once per minute, the small second hand located at the 6 o'clock position also serves as the second hand.

In short, what you need to understand here is that a typical watch structure has the small second hand located at the end of the gears (the fourth wheel).

Understanding the Structure of a Chronograph

Now that you understand the above mechanism, we will explain the structure of a chronograph.

This time, we will take a look at the Venus Cal. 178, which is installed in the Breitling Navitimer.

First, let's look at how the movement of the watch is arranged on the dial side.

Chronograph surface and movement position

If you flip the movement over, you will see that the pink circle is in the position of the small second hand on the dial side.

And for the Venus Cal. 178, the final destination of wheel number 4 is the pink area.

However, it is slightly different from what was explained in the section on three-hand watches, with the three-hand gear placed on the first floor and the chronograph wheel on the second floor.

Therefore, it may be easier to understand if you imagine that gears on the second floor move in the same way as the gears on the first floor.

In other words, there is another gear underneath the pink circle, and that is the gear that powers the three-hand clock.

Next, let's reverse the movements and explain the names and roles of each one.

Explanation of the structure of a mechanical hand-wound chronograph: Venus Cal.178

In this diagram, the button on the bottom right is the start button and the button on the top right is the reset button.

This time, we want you to focus on understanding the movements, so you don't need to remember the names.

However, if you don't understand what these names refer to, it will be difficult to understand what follows, so if you get confused, please come back to this image and check it.

・Operation lever

A long, thin arm connected to the start and stop buttons that rotates the column wheel.

・Braking lever

A brake arm that holds the chronograph wheel in place when the stop button is pressed.

・Sliding gear

The chronograph wheel is mediated by the minute recording wheel next to it, and when it is reset, the gears disengage and the transmission of power is cut off.

・Minute recording wheel (minute counter)

A gear that measures minutes.

・Chronograph bridge (Y)

The bridge that holds the chronograph gears (chronograph runners and minute recording).

Column wheel

This is the most important part, controlling all operations including the stopwatch, and is made up of two layers with gears underneath the pillar.

・Reset hammer

The chronograph wheel and minute recording wheel are reset to zero by striking them with a cam.

・Driving wheel

A wheel that measures seconds.

・Carrying arm

It sits on top of the column wheel and transmits power from the driving wheel to the chronograph runner.

・Chronograph runner (second counter)

An important part of a chronograph that moves the hands of the chronograph.

There are many other things, but if there were too many names it would get confusing, so I've only introduced these here.

How does the chronograph work?

First, let me explain how the chronograph hand in the center moves when you look at the dial.

The pink circular driving wheel and the blue intermediate wheel attached to the carrying arm are always synchronized.

As explained earlier, the pink is the fourth wheel, which rotates once per minute, and when this power is transmitted to the chronograph runner in the center via the blue intermediate wheel, the central chronograph hand and the minute counter synchronized to it begin to move.

In short, the power source provided by the driving wheel (pink) powers the chronograph's second hand, minute counter, and hour counter.

Now let's take a look at the details.

What happens inside the movement when you press the start button

Chronograph movement operation lever and column wheel mechanism

When you press the start button, the operation lever operates, pulling the bottom tip of the column wheel and moving it one notch.

Comparison of the arrangement of the carrying arm, brake lever, and chronograph runner before and after the chronograph is activated

By doing so, the brake lever that secured the column wheel rests on top of the pillar, releasing the brake.

The carrying arm fits into the gap in the column wheel, and the gear that is synchronized with the carrying arm synchronizes with the chronograph wheel, starting the chronograph.

At the same time, the red intermediate wheel also starts moving, and since the red intermediate wheel is synchronized with the yellow-green minute counter, when the chronograph hands start moving, the minute counter also starts moving.

Mechanical hand-wound chronograph: Comparison of the arrangement of each part before and after operation

The top of the reset hammer rests on a pillar, preventing the reset operation from being performed while the chronograph is running.

The lower part of the reset hammer also moves out of contact with the chronograph bridge (Y).

Each part works as explained above.

Now let's look at what happens when it stops.

What happens inside the movement when you press the stop button

Chronograph movement - movement of the reset hammer and regulation spring when the stop button is pressed

By pressing the stop button, the movement transmitted from the operation lever moves the column wheel one notch.

This allows the brake lever to once again fit into the gap in the pillar and hold the column wheel.
The carrying arm rests back on the post and the gear that is synchronized with the carrying arm is released from the chronograph runner.

However, at this time the reset hammer appears to move, but the regulating spring behind it holds the reset hammer in place, so it does not reset.

Each part works as explained above.

Now let's look at what happens when you reset the device.

What happens inside the movement when you press the reset button

As mentioned above, when the stop button is pressed, the bottom of the reset hammer is disengaged from the chronograph bridge.

So, let me explain what's under the chronograph bridge.

The structure of the heart cam beneath the chronograph bridge

The photo on the left shows the watch with the chronograph bridge in place, and the photo on the right shows it with it removed.

If you check the layout again, you will see that the purple circle is the chronograph runner, and the light-green circle is the minute recorder circle.

You can also see that there is a ``heart cam'' in each location, as shown in the image.

Diagram of the placement of the reset hammer when the chronograph stop button is pressed

As mentioned above, when you press the stop, the reset hammer moves away from the chronograph bridge like this.

In addition, the reset hammer is held in position by a regulating spring.
Chronograph - Reset button placement

When the reset button is pressed, the hook holding the regulating spring is released and the reset hammer returns to its home position on the chronograph bridge, striking two cams which reset the chronograph runners (the chronograph hands) and the minute counter.

At the same time, the sliding gear moves up, releasing the brake lever that stops the chronograph wheel.

Each part works as explained above.

This is how the chronograph works.


I thought I'd explained the movement of the chronograph in quite depth, but what did you think?

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