Detailed Guide to Mechanical Watch Craftsmanship, Construction and Operating Principles

Timepieces were invented around the early 16 century, originally using gravity as their source of power. Such timepieces could only be set in a fixed location, such as large clocks hanging in tall buildings or on walls, which utilised iron weights suspended by chains wound around a pulley. Later, the use of spring tension was invented to drive them, which is the mainspring used in clocks and watches today. These timepieces were greatly reduced in size, about the size of an egg, and could be carried in a pocket. This was the Nuremberg Egg invented by a Nuremberg locksmith. Every part of these watches was made entirely by hand, making them labour-intensive and time-consuming, and each watch produced was unique. It was not until the 19 century, with the gradual development of machine manufacturing, that quality could be controlled. To this day, the terminology for watch and clock structures remains extremely inconsistent, with many different names or translations even within the same region, and there is a lack of standardised regulations for watch components worldwide. Consequently, the Swiss ETA movement manufacturer was the first to adopt numbers to represent them, enabling watchmakers to source and match components accurately. However, although movement names among various brands may be the same, structural differences still exist, and the reference codes will vary. The operation of timepieces relies on the lever principle, behaving much like a swinging pendulum going back and forth repeatedly. The most basic operational sequence runs from the mainspring to the centre wheel, third wheel, fourth wheel, escape wheel, pallet fork, and balance wheel, followed by a simple harmonic motion where the reaction force of the balance wheel springs the pallet fork back to its original position.

The barrel is the power source generated by the coiling tension of a steel strip. Generally speaking, the barrel, also known as the first wheel, is composed of the mainspring, barrel drum, and barrel cover, using a ratchet wheel to transmit power to the centre wheel and other gear trains. It is the most vital foundational structure for the operation of a watch, much like the human stomach converting ingested food into energy. Because this simple structure is convenient and effective, it has changed very little from antiquity to the present day.

When you hear a watch ticking away like a metronome swinging ceaselessly, the seconds hand on the dial moves in rhythm with the beat, instantly making us feel the continuous swift passage of time. This rhythmic sound is produced by the balance wheel being subjected to force and reacting back onto the lever. The balance system is made of alloys and utilises a hairspring to create a counter-force, which pushes the impulse jewel pin to spring the lever back. A perfect balance wheel typically oscillates continuously with an amplitude of 225 degrees to 270 degrees, keeping time endlessly alive.

Aside from the previously mentioned mainspring and balance wheel, the main gear train in the middle of a watch's primary structure is also a key component that keeps time running, acting much like human blood constantly receiving the power transmitted from the barrel. This main gear train includes: (1) the centre wheel, also known as the centre wheel or 2nd wheel; (2) the third wheel, also known as the third wheel or 3rd wheel; (3) the fourth wheel, also known as the fourth wheel or 4th wheel; (4) the escape wheel, also known as the fifth wheel or escape wheel. These gears are respectively responsible for transmitting the functions of hours, minutes, seconds, and isochronous rhythm. The beginning of all power starts from the wound mainspring sending force to the centre wheel, third wheel, fourth wheel, escape wheel, and pallet, and then to the balance wheel. The reaction force of the balance wheel then acts upon the pallet fork to restore it to its previous position, allowing the entire operation cycle to repeat endlessly.

In our daily lives, we see the hour, minute, and second hands displayed on watches—how are these distributed via the gear train? When the mainspring supplies power to the centre wheel, the centre wheel rotates at a speed of 1 revolution per 60 minutes. By the time it reaches the third wheel, a gear ratio change begins to occur, and upon transferring to the fourth wheel, it rotates at a speed of 1 revolution per 60 seconds. Therefore, the display of the minute hand is generated by the arbor of the centre wheel, and the display of the seconds hand is generated by the arbor of the fourth wheel. As for the display of the hour hand, it is produced by the hour wheel located on the upper plate and connected to the minute wheel. Most people will notice that some watches have a small seconds sub-dial positioned at the 6 o'clock or 9 o'clock position; this is determined according to the placement of the fourth wheel. In addition, the design of a sweep seconds hand involves fitting an additional transmission gear train to the fourth wheel, allowing the position of the seconds hand to be altered. For watch enthusiasts, after this detailed explanation, has your expertise increased significantly?