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Functionning of a simple mechanical watch

Sketch of a mechanical watch :


The two faces of a mechanical watch :

Geartrain side : This is the side you could see if on the back of your watch there was a glass.
It is from this side is the mechanism that works the watch can be seen.
It is made of the main plate that holds the geartrain, and the bridges.




Terminology of the geartrain

Terminology of the geartrain


When you wind up your watch with the crown, you tighten the barrel spring.

The winding stem winding stemis equipped with a winding pinionwinding pinion,
and a sliding pinion (or wig-wag pinion). sliding pinion

The hole of the wig-wag pinion is square and slides freely on the square part of the stem.

When you wind up your watch, the wig-wag pinion is held against the winding pinion through the yoke.

The square part of the stem drives the wig-wag pinion that in turn drives the winding pinion with its "Breguet" toothing.

Through to the crown wheel, the winding pinion drives the ratchet which is fixed on the square part of the barrel arbor.

The click prevents the ratchet from coming back, that would unwind the spring barrel.

The barrel arbor    The barrel arbor   moves freely in the barrel drum   barrel drum   

The barrel spring    spring barrel     is fixed to the arbor by the hook, and to the drum on the large inner diameter .

spring barrel

To sum up :

When you wind up your watch, you tighten to its maximum the spring around the barrel arbour.

Then, when your watch works, the spring slowly unwind. As a result, it rotates the barrel drum which in turn transmits the driving force to the geartrain.

The driving force reaches the escapement. The escapement transmits gradually the driving force to the balance.

Thanks to this force, the balance swings, and your watch works.

Winding Mechanism side

Winding Mechanism side

This is the side of your watch that is under the dial and the hands.

On this side are the winding mechanism and the hand-setting mechanism.

Winding terminology


Winding terminology


See above for the reassembling

The hand-setting: When you pull the winding stem in order to set your watch, the setting lever, thanks to its stud that enters into the recess of the stem, is set into motion. This move of the setting lever pushes the yoke forward.
Consequently, the sliding pinion engages with the intermediate wheel.
Then, the intermediate wheel engages with the minute wheel that in turn engages with the cannon-pinion, that holds the minute hand, and with the hour wheel, that holds the hour hand.

In the meanwhile, the winding pinion is free and cannot engage the crown wheel because the sliding pinion and the winding pinion are no longer in contact with one another.




1 - Working of a simple mechanical watch

2 - Disassembling a simple mechanical wrist watch

3 - Reassembling a mechanical wrist watch

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