How Does Automatic Watch Work?
Now let’s go into the detail of each of these components!
Diagram showing automatic/mechanical watch movement components
1- Energy Source
Anything that moves need energy. A basic law of physics states that energy cannot be destroyed but can only be converted from one form to another.
The same goes for our automatic/mechanical watch movement. In order for the movement to work, potential energy stored in the mainspring will be transferred to the other components of the watch.
Mainspring is a long striped of steel. It is rolled tightly inside a case called barrel. The spring will try to straighten itself which will turn our watch movement. But how does one tighten the mainspring?
There are two ways to tighten it. One is by rotating the crown which is connected to gears that will tighten the mainspring.
The other one is by a rotor which is basically an eccentric weight that will rotate due to arm’s movement. This is the main feature found in automatic watch.
The rotation of the rotor will then tighten the mainspring. Most automatic watches have both options while mechanical watch has only the crown tightening method.
Modern watches has a clutch to disengage the mainspring when it is fully wound. This is to prevent form over-winding which could damage the mainspring and even the other components.
2- Wheels or Gear Train
The energy stored in the mainspring is transferred to the rest of the watch through a set of wheels or gear train. For those that didn’t know, gears are a set of wheels that is connected through teeth-shaft interface.
Because of this, one full revolution of the shaft (on another wheel) will cause only a small rotation on the teeth connected by it.
By using gears, a small amount of energy from the mainspring barrel (defined by how many times it can rotate) can be used to create a lot of rotations in the wheels that control the second, minute and hour hands. This is one of the important aspect to make a watch has higher power reserve.
How Does Automatic Watch Work? Automatic Watch Movement Diagram
A watch movement diagram. It is the same as the first picture above but shows how the components will be positioned to fit a circular watch. Notice how the wheels are stacked above each other to ensure all of them can be crammed into a small watch.
Escapement is responsible to stop the wheels from spinning freely and out of control. Escapement, and the Controller or Balance Wheel are responsible to maintain the constant rate of rotation of the wheels which in turn will directly affect the accuracy of the watch.
It can be said to act as a brake to control the movement of the whole watch’s gear train.
Escapement consists of an escape wheel (a wheel with odd looking teeth) and forked lever. The escape wheel is connected to the gear train via its shaft while the teeth will be connected to the forked lever.
The forked lever is responsible to lock and unlock the escape wheel causing the escape wheel to move in steps.
The forked lever has a pellet jewel on the contact point with the escape wheel. A jewel material is used to reduce friction and improve longevity of the pallet.
On the other side, the forked lever movement is controlled by the movement of an impulse pin which is controlled by the rotation of the balance wheel.
The forked lever movement is controlled by an impulse pin. The impulse pin will swing side to side following the movement of the balance wheel that it is connected to.
The balance wheel will rock back and forth because it is attached to a hairspring. The hairspring is responsible to rotate the balance wheel and rocking it side to side.
This will moves the impulse pin which hit the forked lever and subsequently releases the escape wheel.
The hairspring is considered one of the most important part in a watch movement as it will absorb and release and equal amount of force at a regular interval. A slight difference will make the watch behave erratically and inaccurate.
The balance wheel oscillates at a very high speed. The vibrations per hour or beats per second is used to track how fast it oscillates.
One beat is defined as one swing of the balance wheel or the impulse pin hit the forked lever once. Typically most watches now have 6 or 8 beats per second.
A higher beat is better as it means the balance wheel is oscillating at a high speed and not really affected by wrist’s movement.
A higher beat will also make the second hand move smoother because the wheel is moving at a finer steps.
The balance wheel, impulse pin, forked lever and escape wheel are the main components which control the accuracy of a watch.
The sound of impulse pin hitting the forked lever and lock and unlock sequence of escape wheel are what give an automatic/mechanical watch movement the characteristic tick-tick sound.
Last but not least, the time indicator. Hands are connected to the wheels that correspond to the time measurement intended.
For example, second hand is connected to a wheel that rotates once in a minute. Minute and hour hand can be connected to other wheels that will rotate at 60 times and 1 time per hour.
I can imagine it will be very hard to understand all of these. Because of that, I’ve attached two excellent videos that will show you in detail how a watch works.