Component record · Train
Count Wheel (Locking Plate)
VerifiedA notched wheel in a clock's striking train whose notches, of varying spacing, determine how many blows are struck at each hour.
What it does
Controls the number of strikes the clock makes at each striking event by allowing a locking detent to drop into a notch cut for that hour's correct count.
How it works
The count wheel's rim is cut with unevenly spaced notches, one series of notches corresponding to each hour's correct strike count (a longer arc before the notch for one o'clock than for twelve o'clock).
As the striking train runs, a lever or detent rides on the wheel's edge; when it reaches a notch, it drops in and locks the striking train, having allowed exactly as many blows as the arc travelled corresponds to.
Because the count wheel is not directly linked to the timekeeping train's actual hour position, if the striking and going trains ever fall out of synchronisation (for example, if the clock is stopped and restarted, or the hands moved without also advancing the striking train correctly), the count wheel will strike the wrong hour until manually corrected.
Evolution
The count wheel (also called a locking plate) was the standard hour-counting method in striking clocks until the rack-and-snail system, self-correcting and directly linked to the hour hand, became preferred in higher-grade and later clocks, although count-wheel striking remained common in simpler and traditional clocks.
Known variations
- Separate count wheel for hour striking
- Combined arrangements handling quarter striking alongside hour striking on additional wheels
Identification for collectors
- A wheel with unevenly spaced peripheral notches, distinct from an evenly toothed gear, found in the striking train
Common failure modes
- Striking train falling out of synchronisation with the going train, causing incorrect strike counts
- Worn notches or detent causing the striking train to skip or over-run
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- Britten, F. J., Old Clocks and Watches and Their Makers
Where sources disagree, the disagreement is stated rather than resolved silently.