Grandfather Clock

Overview

A grandfather clock, properly a longcase clock, is a tall freestanding pendulum clock whose mechanism is powered by falling weights. Its height is functional: the long case gives a heavy weight room to descend over a full week, and it accommodates a seconds-beating pendulum nearly a metre long, whose period sets the rate. Three separate gear trains let the clock keep time, strike the hours, and play a quarter-hour chime melody on a set of tuned rods.

The clock assembles a weight-driven brass mechanism within a tall piece of furniture. The brass Movement sits on the seatboard of the Cabinet, reading the time through the Dial Assembly with its chapter ring and moon-phase complication. Rate is governed by the Pendulum hung behind the movement; energy is supplied by three cast Driving Weight units on cables; the strike and chime hammers sound the Chime Rod Set; the hood and trunk are glazed with the Glass Panel Set; and the weights are raised weekly with the Winding Key / Crank.

How it works

The movement is built between two brass plates spaced by turned pillars, which carry every arbor of the three trains. Each weight, hung over a pulley, drives one train through a ratchet-and-click winding arbor that lets it be wound without running the train backwards.

The time (going) train is regulated by an anchor escapement: its anchor rocks once per pendulum swing, releasing the escape wheel one tooth at a time and returning an impulse to the pendulum through the crutch. The seconds-beating pendulum's rate is fine-tuned by raising or lowering its bob with the rating nut.

At the quarter hours, the chime train is released; a pinned barrel lifts the hammers in sequence to play the Westminster melody on the tubular chime rods, while an air-brake fly governor paces the train at the correct tempo. On the hour the strike train counts out the hour on a separate hammer. Under the dial, the motion works divide 12:1 to drive the hour hand, and a 59-tooth lunar wheel advances the moon-phase disc one step per day.