Section 9: The Eight Driving Forces Behind Mechanical Watch Development
The timekeeping accuracy of a mechanical watch is influenced by many factors. Generally speaking, eight key forces are considered the primary drivers of precision — and by extension, the eight great forces behind the advancement of mechanical watchmaking itself.
At Aorawa Time, understanding what makes a watch tick — literally — is at the heart of everything we do. Here is a deep dive into each of these eight forces.
I. External Influences (External Influence)
Vibration, moisture, air pressure, and shock are all external forces that act on a watch from its surrounding environment. Their impact depends entirely on the conditions in which the watch operates.
Solutions: Anti-shock design, waterproofing, anti-magnetic construction, and protective outer cases. Precision marine chronometers commonly use gimbal mounts to keep the movement level even aboard a vessel at sea.
II. Friction (Friction)
The watchmaker Abraham-Louis Breguet once said: "Give me the perfect lubricant, and I will give you the perfect watch."
Friction plays a dual role in a watch movement. On the positive side, it enables the transmission of power through gear trains, drives the automatic winding rotor, and allows the mainspring to engage with the barrel wall. On the negative side, friction reduces transmission efficiency and causes wear on components, shortening the movement's service life and degrading timekeeping accuracy.
Solutions: Improve lubrication conditions by selecting the appropriate lubricant for each application; use jewel bearings; improve gear tooth profiles; adopt watch-specific tooth forms; and reduce surface roughness values (Ra).
Note: In a watch movement, the gear-to-gear contact and the lever-and-pallet interaction are generally not lubricated, as the viscous resistance of oil in these areas can exceed the friction it is meant to reduce.
III. Regulating Pins (Regulating Pins)
The gap between the regulating pins and the hairspring, as well as the position of the hairspring within the pins, significantly affects isochronism. The regulating pin mechanism is a convenient tool for adjusting the rate of a watch, but both theory and practice confirm that it introduces isochronal errors — errors that are largely random and cannot be fully compensated or eliminated.
Solutions: Minimize the clearance between the regulating pins and the hairspring (to less than twice the hairspring thickness); adopt a free-sprung balance wheel design.
IV. The Escapement (Escapement)
The primary effect of the escapement on a watch is to increase the oscillation period of the balance wheel, causing the watch to run slow.
The balance wheel and hairspring system can only maintain a stable oscillation period when vibrating freely. It is therefore evident that the escapement introduces interference during the energy transfer process. Theory shows that this interference diminishes as the impulse approaches the balance wheel's equilibrium point.
Solutions: The development of the escapement has always pursued the same goals: optimal impulse position, minimal energy loss, and an expanded free-vibration arc (reduced impulse angle). Precision escapements — such as the detent escapement — deliver impulse near the equilibrium point, resulting in a small impulse angle and minimal interference. The lever escapement, with its excellent craftsmanship and ease of adjustment, remains the dominant design in modern mechanical watches, though minimizing the impulse angle remains a key design objective.
Omega developed the co-axial escapement to reduce the escapement's influence on timekeeping. Invented by British watchmaker George Daniels, it is mechanically a hybrid of the lever escapement and the detent escapement.
V. Temperature (Temperature)
Temperature affects timekeeping accuracy in two primary ways. First, temperature changes alter the stiffness of the hairspring, while simultaneously changing the moment of inertia of the balance wheel — directly affecting the oscillation period and timekeeping precision. Second, temperature changes affect the viscosity of lubricating oils, which in turn affects transmission efficiency and timekeeping accuracy.
Solutions: Use a bimetallic temperature-compensating balance wheel; use special alloy materials for the hairspring and balance wheel to provide a degree of temperature compensation within the working temperature range (8–38°C); use high-quality lubricating oils. For extreme temperature conditions — such as the Omega Speedmaster worn on the Moon — dry or solid lubrication methods are employed.
VI. Magnetism (Magnetism)
When exposed to a strong magnetic field, the coils of a magnetized hairspring can stick together, severely disrupting timekeeping. Even without sticking, the hairspring's elasticity undergoes subtle changes that affect accuracy. A magnetic field can also cause the hairspring to deform under its influence, introducing additional stress.
Solutions: Improve the anti-magnetic properties of hairspring materials.
VII. Balance Wheel Poise Error (Out of Poise of the Balance Wheel)
An out-of-poise balance wheel — one that is not perfectly balanced — directly generates positional errors. A perfectly balanced balance wheel is the ideal, but it is practically unachievable; furthermore, the balance wheel's pivot requires clearance in its jewel bearings, and this clearance itself introduces a random positional error.
Solutions: During the production of watch components, perform static poising of the balance wheel first; during movement assembly, perform dynamic poising to further minimize positional errors and comprehensively improve timekeeping performance. The tourbillon, invented by Breguet, also aims to counteract the effect of balance wheel imbalance on timekeeping accuracy by rotating the entire escapement.
Special note: When the balance wheel oscillates at a stable amplitude of 220 degrees, the various impulse forces transmitted to the balance wheel have no effect on its frequency. Based on this principle, some watchmakers have attempted to install a governing mechanism on the escape wheel to keep the amplitude near 220 degrees — though this is difficult to achieve in practice.
VIII. Hairspring Poise Error (Out of Poise of the Hairspring)
A standard flat hairspring does not expand and contract concentrically during operation — its center of gravity constantly moves in a complex pattern near the balance staff. When translated to the balance wheel, this manifests as a balance wheel poise error. The center of gravity shifts with the amplitude of the balance wheel's oscillation and, under the influence of gravity, also generates positional errors.
Solutions: Use a Breguet overcoil hairspring (also known as a Phillips overcoil or double-coil hairspring), which expands and contracts nearly concentrically during operation, with the center of gravity shifting only with the balance angle. Cylindrical or spherical hairsprings offer even better performance but are extremely complex to manufacture and are rarely used in practice, particularly in wristwatch movements. Straight hairsprings have also been used historically.
Precision is not an accident — it is the result of understanding and mastering every force that acts against it. Explore the fine timepieces at Aorawa Time, where every watch is chosen for its mechanical integrity and lasting craftsmanship.