Automatic watch movements are based on those in mechanical watches. But how do automatic watches use the same basic watch movement, but self-wind using the motion of your wrist?
This article will explain how automatic watches work.
A basic mechanical watch movement has 4 parts:
- Balance wheel
When the watch is wound, the mainspring (located in the barrel) is constricted. The spring tries to uncoil, creating the energy that will run the watch. The barrel is connected to a jagged wheel interlocked with the gear train.
The gear train conveys the energy stored in the barrel to the escape-wheel. As the spring unwinds, the barrel turns and drives the wheels of the watch, which are:
- Center-wheel: Turns once every 12 hours to move the hour hand.
- Third wheel: An intermediate wheel.
- Fourth wheel (seconds wheel): Turns once per minute to move the seconds hand.
- Pallet-wheel (escape-wheel): Part of the escapement, it releases the energy transmitted by the gear trains to the pallet-lever.
Then, the gear train broadcasts the force of the mainspring to the balance wheel and increases the swings of the balance wheel. The balance wheel oscillates at regular intervals, which keeps time.
The escapement, which generates the ticking sound in a mechanical watch, ensures that the balance wheel continues to vibrate by providing it with a drive or an impulse at each swing and grants access to the clock’s gear to progress with a specified amount with each swing.
All of the watch components work together to provide accurate timekeeping.
An automatic mechanical watch contains a semicircular ‘rotor’. The rotor is a weight that pivots inside the watch case.
Normal arm and wrist movements cause the rotor to pivot back-and-forth on its staff, which is attached to a ratcheted winding mechanism. The circular motion of the rotor moves a series of gears that then wind the mainspring.
Modern automatic watch mechanisms have two ratchets so that the mainspring winds during both clockwise and counterclockwise rotor motion.
A typical watch’s fully-wound mainspring can store enough energy to run for around two days without being worn. This allows automatic watches to keep running through the night while not being worn. In many cases automatic watches can also be wound manually by turning the crown, so the watch can be kept running when not worn, or in case the wearer’s wrist motions are not sufficient to keep it wound automatically.
Since the watch winds itself, how does it know when to stop?
Early automatic watch models didn’t know. They continued working even after the mainspring was fully wound up, placing excessive tension on the mainspring. This tension could cause it to break, or cause a problem called ‘knocking’ or ‘banking’. Knocking occurred when the excessive drive force applied to the gear train made the balance wheel rotate with too much amplitude, causing the impulse pin to hit the back of the pallet fork horns. This made the watch run too fast, which could break the impulse pin.
To prevent overwinding, a slipping clutch device is used on the mainspring.
Automatic watches are ideal for those wear their watches every day.
What’s your favorite Orient automatic watch?