Mechanical Principles › Complications › Striking mechanisms

CLOCK STRIKING MECHANISMS

The striking mechanism, along with time display, constitutes one of the two fundamental functions of the mechanical Clock. From the appearance of the first foliot movements in the Middle Ages, horologists sought to sound the Time by means of a chime or a Bell, thus complementing the visual reading of the dial with an audible signal. This function met an obvious practical need before the widespread use of artificial lighting: it allowed one to know the Time at night, from a distance, or without consulting the Dial.

Technically, striking the hour requires solving a specific mechanical problem: how to transform an angular position, that of the hand hours, in a defined number of hammer strikes on a bell or a Bell? Several solutions have succeeded one another over the centuries, each corresponding to a different compromise between ease of manufacture, cost, reliability and precision.

The earliest movements, equipped with an escapement with a verge wheel, relied on a no-delay mechanism operated by a trigger, a simple but improvable solution. In the 17th century, the hoop-wheel strike, or count wheel, became widespread in France, introducing a preparation Time, the delay, before the counting of the strikes. In 1676, the English Horologist (watchmaker) Edward Barlow invented the rack strike, where the number of strikes is directly read on a Snail (cam) attached to the Hour wheel, a principle that would become the reference for quality pendulum clocks and repeater watches.

This section presents these three families of striking mechanisms: the striking mechanism with delay via count wheel, the striking mechanism with delay via rack, and the striking mechanism without delay via trigger. For each, the operating principle, the characteristic components, and the historical context of their spread are detailed.

UNTRIPPED STRIKE WITHOUT DELAY

The untripped strike mechanism without delay is the oldest and simplest of the three: it already equipped movements with a verge Escapement, before the widespread use of rack and snail systems. Unlike these, it has no preparation phase (delay).