Component record · Train
Great Wheel (Clock First Wheel)
VerifiedThe first, largest wheel of a weight- or spring-driven clock's going train, mounted on the barrel or on the same arbor as the winding drum or mainspring barrel.
What it does
Receives drive directly from the weight (via a rope or chain wound on a barrel) or from the mainspring barrel, and passes it on, geared down, to the rest of the going or striking train.
How it works
In a weight-driven clock, the great wheel is fixed to (or forms part of) the barrel around which the weight's rope or chain is wound; as the weight descends under gravity, it turns the barrel and great wheel, which meshes with the second wheel's pinion to begin the train's speed-up toward the escapement.
In a spring-driven clock, the great wheel serves the same first-wheel role as the barrel itself, directly analogous to a watch's mainspring barrel, though clock terminology traditionally speaks of the 'great wheel' rather than 'barrel' in many contexts.
Separate great wheels (and separate barrels) are provided for the going train and, in a striking or chiming clock, for each additional striking or chiming train, since each train needs its own independent power source and going arrangement.
Evolution
Fundamentally unchanged in principle across the history of weight- and spring-driven clocks; terminology and exact construction vary by regional tradition (e.g., English longcase practice versus Continental cartel or bracket clock practice).
Known variations
- Great wheel on a rope/chain barrel (weight-driven clocks)
- Great wheel integrated with a mainspring barrel (spring-driven clocks)
- Separate great wheels for going, striking and chiming trains in multi-train clocks
Identification for collectors
- The largest wheel nearest the winding square(s) on the front or back plate of a clock movement
- In multi-train clocks, count the great wheels and winding squares to determine how many trains (going, striking, chiming) the clock has
Common failure modes
- Worn teeth from decades of running, particularly in cheaper or heavily used clocks
- Loose great wheel on its arbor (a riveted or pinned joint working loose over time)
- Rope or chain wear at the barrel in weight-driven clocks, a maintenance item distinct from the wheel itself
Related photographs
No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- Britten, F. J., Old Clocks and Watches and Their Makers
Where sources disagree, the disagreement is stated rather than resolved silently.