How a Mechanical Watch Works

Mechanical watches have no battery, microchip, or circuitry.

Watch parts are machined to near perfection at microscopic sizes and tolerances and can produce accuracy within 2 - 3 seconds per day.

  • Escapement

  • Wheel train

  • Mainspring

Basic functionality

Power is stored in the main spring and released in reliable increments by the oscillating escapement assembly.

The connected gears between the mainspring and escapement (the “wheel train”) turn at various speeds, allowing the watch to “tell time”.

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Time setting & winding

The crown is pulled out to set the time and pushed in to wind the watch.
In each mode (pulled out or pushed in) different gear sets are engaged.

  • Crown & winding stem

  • Yoke

    The yoke moves the sliding pinion and has a spring for outward tension.

  • Sliding pinion

    The sliding pinion has teeth on both sides to engage either setting or winding gear sets.

  • Setting lever

    For setting time, the setting lever presses against the yoke to move it inwards. For winding, the setting lever releases the yoke outwards.

  • Setting jumper

    The setting jumper holds the mechanism in place, and produces a characteristic “click” when switching modes.

  • Mainspring & barrel

    The mainspring is a spiral spring made of steel ribbon.
    It is fitted inside of the mainspring barrel.

  • Click & ratchet wheel

    The click limits ratchet wheel rotation to one direction so the mainspring cannot unwind.

Moving hands

The toothed gears (cannon pinion, hour wheel) that hold time-keeping hands are friction coupled such that with adequate force they can be moved for time setting without disturbing the underlying wheel train gears that continuously drive them.

Mainspring function

The mainspring is connected to the winding pinion at the center and the mainspring barrel on the outside, but the pinion and barrel move independently.

Winding force comes through the pinion, and the click ensures that the spring stays in place so spring power goes out via barrel rotation.

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Wheel train

The wheel train connects the mainspring and escapement, and drives time-keeping hands and associated wheels.

  • Center wheel

    The center wheel rotates once per hour.

  • Third wheel

  • Fourth wheel

    The fourth wheel rotates once per minute and holds the second hand.

Jewel bearings

The axle of each wheel rests in a synthetic jewel bearing. The near- frictionless jewels allow the mechanics to work as long as several decades in some instances.

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Escapement & balance wheel

The escapement (escape wheel and pallet fork) and balance wheel work together to regulate the release of mainspring power in precisely timed increments.

  • Balance wheel

    The balance wheel (most fragile part of the watch) is supported by a
    shock-absorbing mounting system complete with a jewel bearing and capstone which protects the wheel if the watch is dropped, etc.

  • Regulator

    The regulator adjusts the active length of the hairspring which adjusts the speed of the balance wheel oscillation.

  • Impulse pin

  • Curb pins

    Curb pins hold the hairspring in place.

  • Hairspring

  • Pallet fork

  • Pallets

  • Escape wheel

Power exchange

The impulse pin on the balance wheel knocks into the pallet fork (1), releasing the escape wheel so it can rotate (2).

The escape wheel’s teeth (driven by mainspring power) are specially designed to give the pallet fork a “push” (3) which in turn pushes the impulse pin (4), sending the balance wheel into another swing.

Ticking & beats

The pallets catch the teeth of the escape wheel, making a "ticking" noise.

Each incremental escape wheel rotation is called a beat. A common watch beat rate is 21,600 BPH (or “beats per hour”), which is six beats per second.

Motion works

The motion works powers the watch’s hands, translating wheel train rotation into readable time.

  • Minute wheel

  • Minute hand

  • Hour hand

  • Hour wheel

    The hour wheel rotates once per 12 hours.

  • Cannon pinion

Seconds hand

The seconds hand (shown in the introductory illustration) is powered by the fourth wheel in this particular watch movement.

Flow of power

The cannon pinion holds and powers the minute hand.

The slower-rotating hour wheel and hour hand is powered by the cannon pinion through the speed-reducing minute wheel.

Support structure

  • Barrel bridge

    The barrel bridge holds the mainspring and barrel, and associated parts.

  • Train wheel bridge

    The train wheel bridge holds wheel train parts and other assorted elements.

  • Pallet bridge

    The pallet bridge holds balance fork. The shape of the pallet bridge limits pallet fork travel as the fork moves back and forth with the balance wheel.

  • Balance bridge

    The balance bridge holds the balance wheel and regulator.

  • Main plate

    The main plate serves as a base to mount all the movement’s parts.

The full, expanded model

References

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