Cuckoo Clock

Overview

A cuckoo clock is a weight-driven pendulum clock that announces the hour with a mechanical bird and a two-note call imitating the common cuckoo. The pattern was perfected in the Black Forest of southwest Germany in the 18th and 19th centuries, where clockmakers paired ordinary wooden clockwork with a small bellows-and-pipe organ and a carved figure. Power comes entirely from gravity: cast-iron weights disguised as pine cones hang on chains and slowly descend, and the clock is rewound by pulling the chains to haul the weights back up.

The clock splits into a few cooperating groups. The Movement is the going train that keeps time, regulated by the Pendulum swinging behind the carved Carved Case. A separate Strike Train counts and sounds the hours on a coiled gong, and at the same moment it works the Cuckoo Mechanism so the bird, its door, and the whistle pipes act in unison. The Pine-Cone Weight pair drives the two trains through the Chain Set, and the time is read off the Dial & Hands.

How it works

Each train is a stack of brass wheels and steel pinions running between two plates. The going train is held in check by an anchor escapement: at every swing of the pendulum the anchor releases one tooth of the escape wheel, so the train advances in even steps and the hands creep forward at the right rate. Raising or lowering the carved-leaf bob on the pendulum rod lengthens or shortens its swing and trims the timekeeping.

On the hour a lifting lever unlocks the strike train. Its air-brake fly paces the action while a notched count wheel decides how many blows the hammer strikes on the coiled gong. The same train drives two wire lifters that raise and drop the bellows; air pushed from each bellows through its tuned whistle pipe produces one note, and because the two pipes are pitched a minor third apart they sound the falling cuck-oo. In step with the call, a lever tips the carved bird forward and swings the little door open, then lets both close as the train relocks.