TOURBILLON

The tourbillon is a mechanism that can be considered a complication aimed at improving the accuracy of mechanical watches.

Gravity Effect

Since the invention of the balance wheel and its spring, watchmakers have recognized that its precision is affected by gravity when in a vertical position. For example, an imbalance might cause an advance of five seconds per day when the watch is in a vertical position with the crown up. The same watch, in a vertical position with the crown down, would instead delay by five seconds per day.

Abraham-Louis Breguet’s idea, for which he patented the tourbillon in 1801, was to group the entire escapement and regulating organ within a rotating structure, the tourbillon cage. By rotating the regulating organ about its own axis, a mixing of the different adjustments from all the vertical positions is achieved, resulting in a stable and controlled average operation.

This invention offers real chronometric improvements when it comes to a pocket watch, continuously carried in a vertical position. In comparison, the chronometric benefits provided by a tourbillon in a wristwatch are less significant or even nonexistent. However, in most cases, the precision and meticulousness required for the manufacture of a tourbillon are guarantees of particular attention paid to chronometry.

Construction types

There are two types of tourbillon constructions: the pivoted (or between-the-pivots) cage and the flying tourbillon.

The pivoted cage is the construction invented by Breguet. The tourbillon cage rotates around its central axis between the mainplate and the tourbillon bridge in the same manner as a gear train.

The flying tourbillon was developed by the German Alfred Helwig in 1920. Its construction allows for the omission of the cage’s upper pivot and holds the tourbillon cage with a single pivot. This mechanism has the advantage of reducing the thickness of the tourbillon cage. Its major disadvantage is increased friction at the pivot point with a significant lever effect. This type of construction would see a remarkable boom from 1985 with the appearance of precise miniature ball bearings, thereafter systematically used as a bearing and attachment point for the cages of modern flying tourbillons.

Rotation Speed
Depending on its construction, the rotation speed of the tourbillon cage can vary. Logically, higher rotation speeds improve accuracy. However, this has a notable impact on energy consumption and, consequently, the power reserve. Most tourbillon cages complete a full rotation in 60 seconds. Thus, the seconds are often indicated by a hand mounted on the upper pivot of the tourbillon cage or by an index located on its periphery.

Constraints
To be effective in terms of chronometry, the design of a tourbillon must address another delicate balance. To minimise the impact of its movement on both chronometry and the power reserve, a tourbillon cage needs to be as light as possible. This is why titanium is frequently used in its construction. Paradoxically, a balance wheel with greater inertia ensures better timekeeping. Designers of a tourbillon cage must therefore achieve a delicate balance between the inertia of the balance wheel, the inertia of the tourbillon cage, the frequency of the regulating organ, and the power reserve.

Evolution

Modern machinery and technologies or the advent of silicon have enabled the industrialisation of the production of certain components, contributing to the rise and popularity of this complication.