How a watch works

00 / 08 · ETA 6497-1

A hand-wound Swiss calibre, 36.6 mm across, drawn from a CAD model of every part and running. Scroll to take it apart.

CAD model: ETA 6497-1 by Steen Winther, used under the terms of GrabCAD's licensing for non-commercial or internal use. See here for more details.

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Speed

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00How a watch works/ 08

Running now

An ETA 6497-1, as on your wrist, running in real time and set to your local time. Each colour is one job; the plate and bridges that hold it all are in grey.

Three jobs

Turned over. Every mechanical watch does three things. Blue stores energy: the mainspring in its barrel, one turn in 8 hours. Teal lets it out evenly: the escapement and balance, here at half speed. Magenta shows it: the motion works and hands, on the dial side. Flip to see them.

01Power/ 08

Winding

The crown turns the stem. The sliding pinion, held against the winding pinion, turns it; the winding pinion turns the crown wheel, and the crown wheel turns the ratchet wheel on the barrel arbor.

1.1

The click

The click rides up each ratchet tooth and drops behind it, held in by its spring. Let go of the crown and the wind stays in.

The barrel, apart

Lifted apart along its arbor, bridge off: the drum, the spring coiled inside it, the arbor its inner end hooks onto, and on top the ratchet wheel, screwed to the arbor, with the click and its spring. Winding turns the ratchet and arbor; the drum stays put.

The mainspring

Back together, the click holds the arbor and the spring pushes the drum round from the outside: once every 8 hours, for about two days. Its 80 teeth drive the train. Shown 1440 times real speed.

02Gear train/ 08

Bridges off

Under the bridges the train runs from the barrel to the escape wheel, each stage a wheel driving the next pinion. At 100 times real speed the barrel only creeps, the centre wheel turns in 36 seconds and the fourth wheel in 0.6.

1.1

Barrel to centre wheel

The 80-tooth barrel drives the 10-leaf centre pinion: 8 to 1. The barrel turns once in 8 hours, the centre wheel once an hour. Here 800 times faster: 36 seconds and 4½.

1.2

Centre to third

80 teeth on 10 leaves: 8 to 1. The third wheel turns once every 7½ minutes, the other way round. Here 150 times faster.

1.3

Third to fourth

75 teeth on 10 leaves: 7.5 to 1. The fourth wheel turns once a minute; its arbor carries the small seconds. Here 20 times faster.

1.4

Fourth to escape

80 teeth on 8 leaves: 10 to 1. Altogether 600 to 1 from the centre wheel, so the escape wheel turns 10 times a minute, a beat at a time, as the fork lets it. Here twice real speed.

03Escapement/ 08

Locked

Most of the time a tooth of the escape wheel rests on the locking face of one of the fork's ruby stones. The whole train is pushing, and nothing moves until the balance comes back.

Unlock and impulse

The balance swings through. The impulse jewel on its roller enters the fork and flicks it over: the stone slides off the tooth, the tooth pushes the stone, and the fork pushes the jewel back. That push is all the energy the balance gets.

Five parts

One colour each. The escape wheel's teeth meet the two stones in the fork, entry and exit. The fork's slot takes the impulse jewel, which hangs under the roller on the balance staff.

3.1

Lift angle

The jewel is in the fork for about 50° of the balance's swing, 25° either side of the middle. For the rest of the swing the balance is free, and the fork rests against its banking.

Half a tooth a swing

Each swing frees half a tooth: 18,000 swings an hour, 5 a second. That steady stepping is the tick you hear.

04Balance/ 08

The balance

A rimmed wheel on a staff, swinging 2.5 times a second: 18,000 vibrations an hour. Its inertia against the hairspring sets the rate. Slowed ten times here.

Hairspring

A spiral a few hundredths of a millimetre thick, pinned to the staff at the centre and to the cock at the outside. Swung one way it winds up, the other way it opens out, and either way it pulls the balance back.

Regulator

Two curb pins on the index hold the hairspring's outer coil. Where they grip sets how much of the spring does the work, and so how fast the balance swings.

3.1

Toward +

Swing the index toward +. The curb pins slide along the coil toward the centre, the working part of the hairspring gets shorter and stiffer, and the balance swings faster. Every wheel upstream follows it: the watch gains. Exaggerated here to 30 %; a real adjustment is a few seconds a day.

3.2

Toward −

Toward −, the pins slide outward, more of the spring works, it is softer, and the balance swings slower. The whole train slows with it: the watch loses. Watchmakers make this adjustment with the watch on a timing machine.

The Incabloc, taken apart

The balance staff turns on pivots a tenth of a millimetre thick. At each end they run in a shock absorber: a hole jewel the pivot turns in, a cap jewel that takes its end thrust, both in a setting that floats in the bloc, held centred by a lyre spring.

4.1

How they fit

Cut through the staff: the pivot sits in the hole jewel, its tip just under the cap jewel, the two jewels in a setting that sits loose in a conical seat in the cock. The lyre spring on top holds it all down.

4.2

The knock

A knock throws the balance along its staff. The setting and its jewels move with it, the lyre spring gives and pushes them straight back, and the pivot, a tenth of a millimetre thick, does not break.

05Hands/ 08

Dial side

Turned over, time-lapsed: the centre wheel's arbor comes through the plate and carries the cannon pinion, a friction fit. It turns once an hour and will carry the minute hand.

12 to 1

The cannon's 12 leaves drive the minute wheel's 36 teeth, 3 to 1. The minute wheel's 10-leaf pinion drives the 40-tooth hour wheel, 4 to 1. Together 12 to 1: the hour wheel turns once in 12 hours.

Hands on

Back together. The minute hand goes on the cannon pinion and the hour hand on the hour wheel's tube around it, one turn an hour against one in twelve.

Your time

Back to real time. Small seconds at 9 o'clock on the fourth wheel's arbor, once a minute. The hands now show your local time, kept by the balance you just watched.

06Setting/ 08

Pull the crown

The stem slides out 1 mm. The setting lever, sitting in a groove on the stem, swings and pushes the yoke; the yoke pushes the sliding pinion inward, off the winding pinion and onto the setting wheel.

1.1

The keyless works

In place under the dial, one colour each: the stem and its two pinions, the yoke and its spring, the two setting wheels, and the setting lever with its jumper. Pulled out, the sliding pinion turns the setting wheel; the winding pinion stands still.

The hands move

Crown, sliding pinion, setting wheel, intermediate setting wheel, minute wheel. The minute wheel turns the cannon pinion round on its friction fit, and the hour wheel follows. The 6497 has no stop lever, so the seconds keep running while you set.

Push it home

The setting-lever jumper snaps the lever back, the yoke spring returns the sliding pinion to the winding pinion, and the crown winds again.

07Every part/ 08

Exploded

Every part lifts straight off along the axis it turns on, in the order a watchmaker takes them apart. Coloured by job, as in the opening.

1.1

Jewels

Every arbor from the centre wheel to the fork turns in a ruby bearing at each end. Blue: the lower jewels, pressed into the plate. Teal: the upper jewels, set in the bridges, which lift off with them. 17 in all, counting the fork stones, the impulse jewel and the balance's shock settings.

1.2

Bridges

The Swiss layout, one colour each: the barrel bridge (barrel and centre wheel), the train wheel bridge (third, fourth and escape), the small pallet bridge for the fork, and the balance cock. Each comes off on its own, its upper jewels with it.

08Explore/ 08

Take it apart

Every part is live and clickable, coloured by job. Pick a colour in the key to see only those parts. Flip turns it over.

Diameter36.6mm

Jewels17

Rate18 000vph

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