Component record · Regulation
Crutch
VerifiedA forked or pinned arm connecting the pallet arbor of a clock's escapement to the pendulum rod.
What it does
Transfers impulse from the escapement to the pendulum to sustain its swing, and communicates the pendulum's motion back to unlock the escapement at the correct moment.
How it works
The crutch is rigidly fixed to the same arbor as the escapement's pallets (in an anchor or deadbeat escapement), so that as the escape wheel unlocks and the pallets rock, the crutch swings with them.
The crutch's lower end engages the pendulum rod loosely enough to allow for the slight difference in arc between the crutch's swing and the pendulum's own natural motion, typically via a fork embracing the rod or a pin riding in a slot.
Impulse is delivered through this connection each time the escapement unlocks, replenishing the small amount of energy the pendulum loses to air resistance and friction, keeping its amplitude steady.
Evolution
The crutch is fundamental to anchor and deadbeat escapement clocks and has changed little in basic principle since the anchor escapement's introduction.
Known variations
- Fork-type crutch embracing the pendulum rod
- Pin-and-slot crutch connection
Identification for collectors
- The arm connecting the escapement's pallet arbor to the pendulum, visible inside the clock case
Common failure modes
- Worn fork or pin causing excessive play and irregular impulse delivery
- Bent crutch altering beat (the evenness of tick-tock timing)
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.