How a mechanical watch works: interactive 3D guide

All 7 steps

1. 1Turn it over

   Lift the watch and turn it over. Its display back is a sapphire window onto the movement: the steel bridges that hold the wheels, the red ruby jewels their pivots turn in, 21 of them, and the gilded gear train.

2. 2Wind it trap

   Turn the crown. Its stem turns the winding pinion, which turns the crown wheel and the ratchet wheel on top of the barrel, coiling the mainspring inside it tighter. The click, a small sprung pawl, drops into each ratchet tooth with a click, so the spring cannot unwind backwards. Watches differ, typically 20 to 40 turns from empty to full; this one takes 32, for 40 hours. Avoid this trap: When the mainspring is fully wound its coils lie tight round the barrel’s arbor and the crown will not turn any further. Winding up to that stop does the watch no harm; forcing the crown on past it does. The extra force strains the spring where its inner end hooks onto the arbor, which is where a mainspring most often breaks, and makers warn that a forced crown can break the spring or other parts. Here it tears off: the spring flies out against the barrel’s wall, the crown spins on with nothing to wind, and the watch has no power at all until a watchmaker fits a new spring. Wind until the crown stops, then let go.

3. 3The heartbeat

   Slowed down eight times: the balance wheel swings back and forth on its hairspring, 4 times a second. Each swing flicks the pallet fork, which lets the 15-tooth escape wheel go one half-tooth forward, then locks it again, and gives the balance a small push to keep it going. That is the tick: 8 a second, 28,800 an hour.

4. 4The gear train

   The mainspring’s force runs through the gears: from the barrel to the centre wheel (once an hour, carrying the minute hand), the third wheel, the fourth wheel (once a minute, carrying the seconds hand) and on to the escape wheel, where the balance lets it out a tick at a time.

5. 5Take it apart trap

   The glass back comes off first; then, before anything else, the mainspring is let down. Brass tweezers hold the click back off the ratchet wheel while the crown turns slowly back, until the spring is slack and the balance stops. Only then is the stem pulled out and the rest lifted apart into its layers: the winding works; the bridges; the escapement and balance; the gear train and barrel; the main plate with the stem and crown; and on the dial side the motion works, the dial and the hands. Turn it round to look at each part. Avoid this trap: With the balance out, the pallet fork is all that holds the wound mainspring back. Lift the fork out before the spring has been let down and nothing stops the train any more: the barrel drives every wheel round flat out until all its power has run through them, here 40 hours’ worth, the hands whirling round with it. A sudden rush like that breaks pivots and strips teeth; here three teeth come off the escape wheel, the fastest of the wheels. Let the mainspring down first: hold the click back off the ratchet wheel and let the crown turn slowly back until the spring is slack, then take out the balance, the pallet bridge and the pallet fork.

6. 6Put it back together

   The layers go back together in the reverse order and the stem goes back in. The crown then winds the mainspring up again, 32 turns; once the spring’s force reaches the balance through the train it starts swinging, and the watch is turned face up.

7. 7A day later

   Speeded up 21,600 times: a whole day in four seconds. The hour hand goes round twice, the minute hand 24 times, the balance beats 691,200 times, and the power reserve falls from 40 hours to 16.

What is in it

• Mainspring in its barrel · stores the energy
• Gear train · centre, third and fourth wheels
• Escapement · escape wheel and pallet fork
• Balance wheel and hairspring · the timekeeper
• Winding and setting works · crown, stem, pinions, click
• Motion works, dial and hands · on the dial side
• 21 jewels · synthetic rubies the pivots turn in

Questions

Safety

Opening a watch exposes its movement to dust and moisture, and its parts are tiny: leave servicing to a watchmaker.

• Lithium-ion batteries: never bend, puncture or pry a battery with metal. A damaged cell can go into thermal runaway: it smokes, catches fire and can explode. Discharge it below 25% first; if it swells, hisses, smokes or gets hot, stop and move it somewhere safe.
• Static (ESD): work on an anti-static mat with a grounded wrist strap; a spark you cannot feel can kill a chip.
• Power off: switch the device off and unplug its charger before you open it, and disconnect the battery before touching anything else inside.

About this guide

3D Spatial Reconstruction: Models are engineered from factual hardware measurements to visualize internal layouts, screw lengths, and hidden cable traps before you open your device. Always verify cable routing on your specific hardware revision.

The watch here is of our own design, a typical hand-wound movement with small seconds: 28,800 beats an hour (4 swings of the balance a second, 8 ticks), a 15-tooth escape wheel, 21 jewels and 40 hours of power reserve. Its gearing follows from those numbers: the fourth wheel turns once a minute, the escape wheel 16 times a minute, the centre wheel once an hour.

Real watches differ: many beat 21,600 times an hour, and fully winding one takes from about 20 to 40 turns of the crown. The day-long speed-up is 21,600 times: 86,400 seconds in four.

The two traps play out what watchmakers and makers warn about: a crown forced on past full wind, which can break the mainspring (here it tears off the arbor’s hook, where mainsprings most often break), and a pallet fork taken out with the spring still wound, which lets the train run away (here it strips three teeth off the escape wheel). How each break looks is our own picture.

Sources: Farer: how to wind a mechanical watch (stop once the crown will not turn; forcing it risks the movement), Shinola: winding guide (about 30 turns for a 42-hour reserve; stop at the resistance, never force it), Orient (Epson) user’s guide: a fully wound crown stops turning, and forcing it can break the mainspring, Wikipedia: mainsprings break most often where they hook onto the arbor; winding to the stop is not overwinding, Horopedia: letting a mainspring down, by the click and the crown, before any disassembly, Horlogerie-Suisse: taking a hand-wound movement apart (the spring let down with tweezers on the click first), Worn & Wound, Watchmaker’s Bench: without the pallet fork the train spins freely, US patent 157,913 (D. Gruen, 1874): a spring’s force reaching the train at once breaks teeth and pivots, Horopedia: Incabloc, the balance’s shock jewels held by a lyre spring, Price source: Mido US, complete service of a 2–3 hand mechanical watch, $210, Price source: Longines US, full service of a 2–3 hand mechanical watch, $380.

The 3D models, drawings and text are our own. The device shown is a generic one of our own design, not any one maker’s model.