lever escapement


  • This means that in order to unlock the wheel it must be turned backwards by a small amount, which is done by the return momentum of the balance wheel via the impulse pin.

  • An escapement is a mechanical linkage that delivers impulses to the timepiece’s balance wheel, keeping it oscillating back and forth, and with each swing of the balance wheel
    allows the timepiece’s gear train to advance a fixed amount, thus moving the hands forward at a steady rate.

  • The impulse received by the entrance pallet as the tooth moves over the impulse face is transferred by the lever to the balance wheel via the ruby impulse pin on the roller
    of the balance wheel.

  • In the pin pallet escapement, these two faces are designed into the shape of the escape wheel teeth instead, eliminating complicated adjustments.

  • To get started, the lever fork must receive a small impulse from the anti-clockwise rotation of the balance wheel via the impulse pin (say by being shaken) which rotates the
    lever slightly clockwise off the left banking pin.

  • [3] Draw The reliability of the modern lever escapement depends upon draw; the pallets are angled so that the escape wheel must recoil a small amount during the unlocking.

  • Once the entrance tooth leaves the impulse plane of the entrance pallet, the wheel is able to turn a small amount (called the drop) until the exit tooth of the escape wheel
    lands on the locking face of the exit pallet.

  • From the release from the entrance pallet to this point, the escape wheel will have turned through exactly one half of the 24 degree angle between two teeth.

  • This will unlock the escapement, releasing the escape wheel so that the exit tooth can slide over the impulse plane of the exit pallet, which transfers a clockwise impulse
    to the balance wheel’s impulse pin via the lever fork, while pushing the lever up against the left banking pin.

  • These pallets are attached solidly to the lever, which has at its end a fork to receive the ruby impulse pin of the balance roller which is fixed to the balance wheel shaft.

  • Each back and forth movement of the balance wheel from and back to its center position corresponds to a drop of one tooth (called a beat).

  • As shown in the diagram, the escape wheel rotates clockwise and the entrance tooth is locked in place against the entrance pallet, the lever held in place by the left banking

  • Third, it is self-starting; if the watch is jarred in use and the balance wheel stops, it will start again.

  • The escape wheel drops again until the entrance tooth locks on the entrance pallet now being held in place by the left banking pin via the lever.

  • At rest one of the escape wheel teeth will be locked against a pallet.

  • The escape wheel has specially shaped teeth of either ratchet or club form, which interact with the two jewels called the entrance and exit pallets.

  • Advantages The advantages of the lever are, first, that it is a “detached” escapement; it allows the balance wheel to swing completely free of the escapement during most of
    its oscillation, except when giving it a short impulse, improving timekeeping accuracy.

  • The lever is mounted on a shaft and is free to rotate between two fixed banking pins.

  • The balance wheel is returned towards its static center position by an attached balance spring (not shown in the diagram).


Works Cited

[‘Britten, Frederick James (1899). Old Clocks and Watches and their Makers. London: B. T. Batsford. pp. 349–350.
1. ^ Jump up to:a b Glasgow, David (1885). Watch and Clock Making. London: Cassel & Co. pp. 180-183.
2. ^ “Westime | Fun & Educational
| What Makes a Watch Tick?”. Archived from the original on 2013-10-07. Retrieved 2013-10-05.
3. ^ Treffry, Timothy (2006-05-30). “Heart of Lightness” (PDF). QP Magazine. Vol. 15, no. 24. London. pp. 86–91. Retrieved 2018-03-20.
Photo credit: https://www.flickr.com/photos/johnath/7193058132/’]