Section 5: Essential Technical Knowledge for Watchmaking

Section 5: Essential Technical Knowledge for Watchmaking

For anyone working in watchmaking — whether in sales, service, or manufacturing — a solid foundation in the underlying technical principles is indispensable. This section covers the essential knowledge every watch professional should understand: gear transmission ratios, electrical units, magnetism, electromagnetics, timekeeping principles, watch construction, tolerances and fits, geometric tolerances, and heat treatment.

I. Calculating Watch Gear Transmission Ratios

Based on the characteristics of watch mechanisms, the industry defines the transmission ratio as the ratio of the speed of the driven shaft to the speed of the driving shaft. The relationship between transmission ratio and tooth count is:

Transmission Ratio (gear speed ratio) = Driver Gear Teeth ÷ Driven Gear Teeth

In structural design, the watch’s fixed transmission ratios must be maintained: 1 hour = 60 minutes, 1 minute = 60 seconds, and the hour hand completes one revolution in 12 hours or 24 hours.

II. Types of Watch Transmission Ratios

Transmission ratios fall into three types:

• Speed-increasing transmission — transmission ratio greater than 1
• Speed-reducing transmission — transmission ratio less than 1
• Constant-speed transmission — transmission ratio equal to 1

III. Unidirectional and Bidirectional Transmission

Unidirectional transmission refers to a gear train in which the relationship between the driving and driven elements remains constant throughout operation. For example, in timekeeping transmission, the driving element is always the wheel plate and the driven element is always the pinion.

Bidirectional transmission refers to a gear train in which the driving and driven relationship reverses in different stages of operation. For example, in the seconds wheel-to-minute wheel train: during timekeeping, the seconds wheel is the driver and the minute wheel plate is the driven element; during hand-setting, the setting wheel drives the minute wheel plate, which in turn drives the seconds wheel — so the minute wheel plate becomes the driver and the seconds wheel becomes the driven element. The meshing of the seconds wheel with the minute wheel plate, and the meshing of the minute wheel plate with the setting wheel, are therefore called bidirectional transmission. Additionally, the setting mechanism can set hands both forward and backward, and the timekeeping train can run both forward and in reverse.

IV. Units of Voltage, Current, Resistance, and Capacitance

The unit of voltage is the Volt (V), commonly abbreviated as “volt.”

The unit of resistance is the Ohm (Ω), commonly abbreviated as “ohm.”

The unit of current is the Ampere (A), commonly abbreviated as “amp.” Smaller units include the milliampere (mA), microampere (μA), and nanoampere (nA). Watches commonly use microamperes; quartz clocks commonly use milliamperes. All are decimal multiples.

The unit of capacitance is the Farad (F), commonly abbreviated as “farad.” The farad is an extremely large unit; practical units are the microfarad (μF) and picofarad (pF), where 1F = 10⁶ μF and 1μF = 10⁶ pF.

V. Basic Knowledge of Magnets

Objects that can attract iron, steel, and similar materials are called magnets; materials with this property are called ferromagnetic materials. The ends of a magnet, where the attractive force is strongest, are called the magnetic poles. A compass needle is a small permanent magnet: one end points south (marked S) and the other points north (marked N).

Natural magnets have very weak magnetism. Modern industry uses artificial magnets — made from iron, cobalt, nickel, samarium-cobalt, and other materials, processed and magnetized, commonly known as “magnetic steel.” The rotors in quartz watch motors commonly use samarium-cobalt alloy and neodymium-iron-boron materials.

VI. Basic Knowledge of Electromagnetism

A magnetic field exists around every magnet. Scientific experiments have also shown that a magnetic field exists around a current-carrying conductor. A simple experiment: wrap a nail with metal wire and connect the two ends of the wire to a dry battery — this creates a basic electromagnet. The coil in a quartz electronic clock operates on exactly this principle: the coil converts electrical energy into magnetic energy.

VII. Testing Battery Condition

A quartz electronic watch operates normally at a battery voltage of 1.55V. As voltage drops, frequency decreases and the watch runs slow. The voltage measured by a multimeter is the open-circuit voltage, not the battery’s working voltage — this figure has limited practical value. The correct measurement is the load voltage (voltage under working conditions), which must not fall below 1.55V.

The Weiz 6000 quartz watch tester incorporates a device for measuring battery load voltage. Method: place the battery positive terminal in the instrument’s designated position, connect the black probe to the negative terminal, and simultaneously press the instrument’s load button. The display shows the “load voltage,” which must not be below 1.55V. Theoretically, battery capacitance should also be measured, but this is a destructive test and is generally not performed.

VIII. The Basic Principle of Timekeeping Instruments

The oscillation system of a timekeeping instrument must have a constant oscillation period and must oscillate continuously without decay. Time is calculated by counting the number of oscillations of the process being measured:

Time = Oscillation Period × Number of Oscillations

IX. The Composition of a Watch

Whether mechanical or quartz, every watch is composed of two major parts: the movement and the exterior components. Everything except the movement is classified as an exterior component — defined as the parts that are visible to the wearer.

X. The Composition and Function of Watch Exterior Components

1. Composition of Exterior Components

Exterior components are the visible parts of the watch: case, crystal, caseback, crown, water-resistant tube, dial, hands, and strap. There are also invisible connecting components between the movement and the case: movement ring, movement holder, and movement screws, as well as the water-resistant gasket.

2. Functions of Exterior Components

(1) Reading instantaneous time.

(2) Aesthetics. Aesthetics is critically important — it encompasses the wearer’s values, traditions, culture, aesthetic sensibility, and personal worth. The brand and exterior components account for a very large proportion of the total watch price.

(3) Protecting the movement. Protection of the movement refers to the sealing performance of the case — commonly known as water resistance.

XI. Tolerances and Fits

1. Nominal Dimension — The dimension specified in the design. Marked in a prominent central position in standard font.

2. Upper Deviation — The upper limit of permissible deviation from the nominal dimension. Marked at the upper right of the nominal dimension in smaller font.

3. Lower Deviation — The lower limit of permissible deviation from the nominal dimension. Marked at the lower right of the nominal dimension in smaller font.

4. Clearance Fit — In a hole-and-shaft fit, when the hole dimension minus the shaft dimension is positive, a clearance exists between hole and shaft, allowing free relative movement. Also called a running fit.

5. Interference Fit — In a hole-and-shaft fit, when the hole dimension minus the shaft dimension is negative, an interference exists between hole and shaft. The hole and shaft are locked together and cannot be separated without force. Also called a press fit or static fit.

6. Transition Fit — In a hole-and-shaft fit, the tolerances of hole and shaft overlap. Any given pair may have either clearance or interference — a special fit type that can be either at different times.

XII. Basic Knowledge of Geometric Tolerances

Watch professionals should understand the basic principles of mechanical transmission, electrical fundamentals, tolerances and fits, and heat treatment. Table 1–1–4 below lists the items and symbols for geometric (form and position) tolerances used in mechanical machining:

Note: Table content provided by Yang Junfeng.

XIII. Basic Knowledge of Heat Treatment

Watchmaking cannot exist without metallic materials; manufacturing watches requires machining; and machining cannot exist without heat treatment of materials. The following is a brief introduction to the fundamentals of heat treatment.

Critical Temperature — The temperature at which the microstructure of a solid iron-carbon alloy transforms. Different carbon content steels have different critical temperatures. In practice, heating a steel component to red-hot corresponds to a critical temperature of approximately 800°C.

Quenching — Heating the workpiece above the critical temperature, holding for a period, then rapidly cooling in water or oil. The purpose is to increase the hardness of the metal.

Annealing — Heating the workpiece above the critical temperature, holding for a period, then slowly cooling. The purpose is to reduce metal hardness (facilitating machining), prepare for subsequent quenching, and relieve internal stresses in the material.

Tempering — Heating the quenched steel component below the critical temperature, holding for a period, then cooling in air or oil. The purpose is to eliminate the brittleness and internal stresses introduced by quenching, bringing the workpiece to its specified hardness and toughness.

The Science Behind Every Watch on Your Wrist

From gear ratios to heat treatment, from magnetic principles to geometric tolerances — every watch is a masterclass in applied physics and precision engineering. At Aorawa Time, we bring this heritage of technical excellence to every piece we offer:

• Men’s 42mm Skeleton Automatic Watch — witness the gear train, escapement, and balance wheel in motion on your wrist.
• Men’s Full Diamond Octagonal Luxury Watch — precision engineering meets uncompromising luxury.
• Vintage Leather Apple Watch Band — handcrafted quality for the modern wrist.