How it works
Mechanisms & Escapements
A mechanical timekeeper does three things: it stores energy, it counts, and it releases energy in counted portions. Everything else — fusees, trains, escapements, compensation balances — exists to make those three operations more nearly constant.
Power to oscillator
The gear train, stage by stage
- 01Mainspring / weightStores the energy that drives everything downstream.
- 02Barrel or fuseeDelivers that energy to the train, ideally at constant torque.
- 03Centre wheelTurns once per hour and carries the cannon pinion.
- 04Third wheelSteps the ratio up toward the escapement.
- 05Fourth wheelTurns once per minute; carries the seconds hand.
- 06Escape wheelReleased tooth by tooth by the escapement.
- 07EscapementCounts oscillations and impulses the oscillator.
- 08Balance or pendulumThe time base whose period sets the rate.
Escapement explorer
Compare escapements
Working principle
Lever escapement
A pivoted lever with two jewelled pallets locks the escape wheel and transmits impulse to the balance through a fork and impulse pin, leaving the balance detached for most of its arc.
Attributed to Thomas Mudge, c. 1754; developed through the nineteenth century
Advantages
- Robust
- Self-starting
- Good isochronism
- Suits mass production
Drawbacks
- More parts than frictional-rest designs
- Requires accurate pallet geometry
Found in
railroad-watches · hamilton-992b · waltham-model-1883
Regulation
Keeping the rate constant
Balance and hairspring
The oscillator's period depends on the balance's moment of inertia and the spring's stiffness. Everything in regulation is an attempt to keep both constant.
Temperature compensation
Bimetallic balances flex their rims to offset thermal change; later monometallic balances rely on Elinvar-type hairspring alloys instead.
Isochronism
Breguet overcoils, correct terminal curves and efficient escapements keep rate stable as amplitude falls with the state of wind.
Positional adjustment
Poising the balance and correcting beat error reduce the rate differences between dial-up, dial-down and the pendant positions.
Beat error
Asymmetry between the two halves of the vibration wastes amplitude and can prevent a watch self-starting.
Pendulum regulation
In clocks, rate is set by effective pendulum length; gridiron, mercury and Invar pendulums address thermal expansion.