Inside the Mechanical Watch

This post focuses on mechanical and automatic watches.   Further, watches can have many types of complications (additional features like day/date window) that add to the complexity of a watches’ internal workings.  For this post, I am focusing on the basic internals.

Automatic / Mechanical Watches

An automatic watch is a type of mechanical watch that has a self-winding feature. The self-winding feature of the watch is driven by a weighted semicircular rotor that winds a mainspring.  Before we get too far into the technicalities of this type of watch, we need to understand that a watch has five basic components.

Power source
Gear train
Control / Balance wheel
Time Indicator

(1) Power Source

For anything to move it needs an energy force. Mechanical watches use the basic law of physics that states that energy cannot be destroyed but will be converted into another form. For a mechanical watch to work, energy will need to be stored and this is done with a mainspring. The mainspring is a strip of coiled steel wound around an arbor and held inside a mainpsring barrel. The mainspring’s natural attempt to unwind is the source of stored energy. Automatic watches wind the mainsrping with a weight that moves as the wearer’s arm moves while a mechanical watch must be wound by a crown. Additionally, automatic watches often can be wound with a crown.

(2) Wheels / Gear Train

The energy stored in the mainspring is released through a series of gears (gear train).  By using gears, a small amount of energy from the mainspring barrel can create many rotations in the wheels that drive the hands of the watch.

(3) Escapement

The escapement is responsible for keeping the gears from spinning freely and controls the speed of the gears. The escapement is made up of an escape wheel (gear with odd-looking teeth) and a forked lever. The forked lever is designed to lock and unlock the escape wheel (also the source of the ticking sound).  The forked lever has what are called pallet jewels at the contact points with the escape wheel to reduce friction and allow the parts to last longer.  The other end of the forked lever is controlled by the movement of the impulse pin which is attached to the balance wheel.

(4) Balance Wheel / Control Wheel

The forked lever is moved by an impulse pin positioned on the balance wheel. The impulse pin moves with the rhythm of the balance wheel. The balance wheel is connected to the most important part of the watch – the hairspring.  The hairspring sits in the center of the balance wheel and rocks the balance wheel at a very high speed. Vibrations per hour are used to track the speed. Higher vibrations will result in a second hand that moves smoother versus ticking.

(6) Time Indicator

The hands of a watch are connected to gears that correspond to the time measurement.  So, the minute hand is connected to a gear wheel that spins 1 revolution per minute.  The same goes for the second and hour hands.

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