Mechanical Principles › Complications › Striking mechanisms › Clock striking mechanisms

STRIKING MECHANISM WITH HOOD DELAY

Origin and principle

The chaperon striking mechanism, also called count wheel striking, is among the oldest solutions used to automatically strike the hours; it became widespread in Europe, particularly in France, as early as the 17th century, before durably equipping Paris clocks and many longcase clocks. As in any striking clock, the Train (wheel train) that drives it, separate and distinct from the Movement Train (wheel train), only communicates with the latter through the Release interface; it has its own Barrel or its own driving weight. Its characteristic component, the chaperon, is a Disc with an irregular profile comprising twelve notches of different depths, one per hour, which performs one complete Lathe every twelve hours, independently of the Hour wheel itself.

Components and Operation

A trigger, hinged and returned by a spring, permanently rests on the profile of the snail: the depth of the notch reached determines the number of strikes made before the trigger falls back into the next notch and stops the striking. The Release of the sequence, however, is not immediate: it is preceded by a delay provided by a delay wheel, a small wheel fitted with a pin that comes to rest against the stud of a secondary trigger passing through the front Main plate via a narrow slot. This preparatory phase positions the entire mechanism before the striking Train (wheel train) is actually released and drives the hammers. This so-called passing strike automatically strikes the full hour, and often a single strike at the half hour, without any intervention from the user.

Structural limitation

The inherent weakness of this system lies in the mechanical independence of the snail from the Hour wheel: nothing ensures that the number of strikes sounded corresponds to the time actually displayed. Incorrect handling of the hands, particularly setting the time without going through the striking mechanism, can thus permanently desynchronize the two functions, a flaw that will be corrected by the rack striking mechanism.