7 steps · 29 parts in 7 layers · 28,800 beats an hour
How a mechanical watch works: interactive 3D guide
A hand-wound mechanical watch opened up in 3D: how the spring stores the energy, how the balance and the escapement turn it into 8 ticks a second, and how the gears carry it to the hands. Press play to watch a step, drag to look around, or switch to Drawing for a technical drawing’s black lines.
What is inside
A hand-wound mechanical watch: no battery, just a coiled spring, a train of gears and a balance wheel swinging back and forth 4 times a second. Its 29 parts sit in 7 layers, from the glass back down to the hands.
- Wind a hand-wound watch at about the same time each day, until the crown stops turning.
All 7 steps
- 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.
- 2Wind it
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.
- 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.
- 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.
- 5Take it apart
Lifted apart into its 7 layers: the glass back; 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.
- 6Put it back together
The layers go back together in the reverse order. Once the balance is free it starts swinging again, the spring’s force reaching it through the train, and the watch is turned face up.
- 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
How does a mechanical watch work without a battery?
A coiled mainspring stores the energy you put in by winding. A train of gears carries its force to the escapement, which lets it out a tick at a time, and the balance wheel on its hairspring sets the pace.
What does 28,800 beats per hour mean?
The escapement ticks 8 times a second: the balance swings back and forth 4 times a second. Many watches beat at 21,600 an hour, 6 ticks a second.
What are the jewels in a watch for?
They are synthetic rubies that the pivots of the wheels turn in: hard and smooth, so the pivots wear less and turn with less friction.
How many times should I turn the crown?
Until it stops: typically 20 to 40 turns from empty, depending on the movement. Once a day keeps a hand-wound watch running.
What is the power reserve?
How long the watch runs on a full wind: 40 hours here. A day later it still has 16 hours left.
Safety
Opening a watch exposes its movement to dust and moisture, and its parts are tiny: leave servicing to a watchmaker.
About this guide
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.
Sources: Farer: how to wind a mechanical watch, Shinola: winding guide (about 30 turns for a 42-hour reserve).
The 3D models, drawings and text are our own.