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The Encyclopedia of Horology

Component record · Escapement

Escape Wheel

Verified

The last and most specialised wheel of the going train, shaped to interact with the escapement's locking and impulse elements.

What it does

Releases the train's stored energy in small, regular increments and delivers impulse to the balance (or pendulum) via the pallets.

How it works

The escape wheel's teeth are shaped specifically for its escapement type: pointed for the verge's crown wheel, club-toothed for the club-tooth lever escapement, or ratchet-toothed for the duplex and chronometer detent escapements. Its geometry is inseparable from the escapement design it belongs to.

In a lever escapement, the escape wheel is repeatedly locked and released by the pallet fork's entry and exit pallets. Each release lets one tooth escape (hence the name) and, in doing so, that tooth's inclined face pushes on the pallet, transferring a small, repeatable impulse of energy to the balance via the fork and impulse pin.

Because this cycle repeats at the balance's beat rate (commonly several times per second in a modern watch), the escape wheel and its cooperating pallets are subject to continuous, minute wear, and their geometry — tooth count, undercut, and locking/impulse face angles — is central to a movement's rate stability and efficiency.

Evolution

Escape-wheel design tracks escapement history closely: crown-wheel teeth for the verge, ratchet teeth for the duplex, club teeth for the lever; lighter materials and, recently, silicon and other non-magnetic, self-lubricating materials have been introduced in high-end modern movements.

Known variations

  • Verge (crown) escape wheel
  • Cylinder escape wheel with raised teeth
  • Duplex escape wheel with two sets of teeth
  • Lever escapement club-tooth escape wheel
  • Chronometer (detent) escape wheel

Identification for collectors

  • Tooth shape is diagnostic of escapement type and therefore a key dating and classification tool for a movement

Common failure modes

  • Tooth wear and chipping
  • Rust on steel escape wheels
  • Bent teeth from shock

Photographs

Watch movement
Watch movement — Harry Chase Brearley, Public domain. Wikimedia Commons file page
PSM V46 D075 Watch escape wheel swiss lever and balance
PSM V46 D075 Watch escape wheel swiss lever and balance — Unknown authorUnknown author, Public domain. Wikimedia Commons file page

Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.

Sources & references

  1. Gazeley, W. J., Clock and Watch Escapements
  2. Daniels, G., Watchmaking

Where sources disagree, the disagreement is stated rather than resolved silently.