Mechanical principles → Complicated mechanisms

SWISS LEVER ESCAPEMENT

The Swiss lever escapement is valued for its robustness, accuracy, and relative ease of manufacture. From the moment it appeared, this escapement quickly became the industry standard due to its technical merits and economic viability.

History

The Swiss lever escapement emerged in the second half of the 19th century as an improvement on the older, less efficient English lever escapement. Around 1842, Swiss watchmaker Georges-Auguste Leschot played a pivotal role in the industrialisation of this mechanism, enabling its widespread adoption. Over the decades, Swiss manufacturers refined the design, establishing it as a cornerstone of modern mechanical watchmaking.

Escapement Type

The Swiss lever escapement belongs to the family of detached escapements, which means there is no continuous contact between the escapement and the oscillator, allowing the balance wheel to swing freely between impulses.

Component Overview

The Swiss lever escapement comprises the following elements:

  • Escape Wheel: Typically made from steel, nickel-phosphorus (via UV-LIGA technology), or silicon (via DRIE micromachining).

  • Lever: Usually constructed from steel with synthetic ruby pallets, though entire levers may also be produced in nickel-phosphorus or silicon.

  • Impulse Pin Assembly (Double Roller): This consists of a large and a small roller, joined by a staff. It is generally made from ductile materials capable of withstanding impact (such as brass or CuBe alloys). Silicon is unsuitable for this purpose due to its brittleness. The impulse pin, typically made of synthetic ruby (corundum), is inserted or glued into the larger roller.

Advantages

  • Accuracy: The Swiss lever escapement is a mature and refined mechanism capable of achieving excellent chronometric performance.

  • Reliability: It performs well under shock and in varied positions, making it ideal for wristwatches.

  • Industrial Scalability: Regardless of the materials used in its components, the Swiss lever escapement can be mass-produced efficiently and cost-effectively.

  • After-Sales Servicing: Except for silicon versions, the Swiss lever escapement allows for conventional escapement adjusting, regardless of the watch’s age.

Drawbacks

  • Friction: Although materials such as steel and synthetic ruby, or silicon, are chosen to reduce friction, sliding friction between components remains significant. In particular, the steel teeth of the escape wheel interact with the ruby pallets of the lever via sliding contact. The Swiss lever escapement alone can consume approximately 30% of the mainspring’s nominal energy. Silicon variants now offer improved efficiency.

  • Maintenance: Traditional constructions (steel and ruby) require careful lubrication, which must be reapplied periodically to maintain optimal performance and minimise wear. Silicon-based escapements offer a solution here, as most can operate entirely without lubrication.