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The Encyclopedia of Horology

Component record · Power

Barrel

Verified

A cylindrical drum, toothed on its outer circumference, that houses the mainspring.

What it does

Contains and protects the mainspring while transmitting its stored torque to the going train via the barrel teeth meshing with the centre pinion.

How it works

The barrel comprises a toothed drum and a cover (barrel cap or cover plate) that closes over the coiled mainspring, with a central arbor onto which the spring's inner coil is hooked or, in later designs, secured by a slipping bridle.

In a going-barrel watch the barrel teeth mesh directly with the centre wheel pinion, so the barrel itself is the first wheel of the train; in a fusee watch the barrel instead pulls a chain that winds onto the fusee cone, and it is the fusee, not the barrel, that meshes with the train.

The barrel arbor is squared or slotted at one end to accept the winding mechanism (key square, or ratchet wheel and click assembly in keyless watches).

Evolution

The going barrel superseded the fusee in mass production because it is cheaper, thinner and simpler to manufacture, once lever escapements reduced sensitivity to torque variation; fusee barrels persisted longest in high-grade English work and marine chronometers.

Known variations

  • Going barrel (drives the train directly)
  • Fusee barrel (drives a chain to a separate fusee cone)
  • Twin-barrel or multiple-barrel arrangements used for extended power reserve

Identification for collectors

  • Going-barrel watches show the barrel teeth engaging the centre wheel directly beneath the top plate
  • Fusee watches show a chain running from the barrel to a stepped conical fusee
  • Barrel cap removal reveals the coiled spring; a lubricated, evenly coiled spring is a good service sign

Common failure modes

  • Worn or chipped barrel teeth causing rough running or skipping
  • Cracked or distorted barrel cap
  • Wear at the arbor pivot holes leading to poor meshing depth

Photographs

Going barrel
Going barrel — Frederick J. Britten, Public domain. Wikimedia Commons file page
Watch mainspring barrel
Watch mainspring barrel — Harry C. Brearley, 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. Daniels, G., Watchmaking
  2. de Carle, D., Watch and Clock Encyclopedia

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