TOURBILLON
The tourbillon is a mechanism that can be considered a complication aimed at improving the accuracy of mechanical watches. 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.
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.
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.
Depending on the construction, the rotational speed of the tourbillon cage can vary. Logically, accuracy is increased with higher rotational speed. This, unfortunately, has a remarkable impact on energy consumption and therefore the power reserve. The majority of tourbillon cages complete a full rotation in 60 seconds. Thus, the seconds are frequently indicated by a hand mounted on the cage’s upper pivot or an index placed at its periphery.
To be efficient in terms of chronometry, the design of a tourbillon faces the challenge of balancing another compromise. To limit the impact of its movement on chronometry and power reserve, a tourbillon cage must be as light as possible, which is why titanium is often used in its manufacture. Paradoxically, a balance wheel with great inertia guarantees better chronometry. It is, therefore, a delicate balance between the inertia of the balance wheel, that of the tourbillon cage, the frequency of the regulating organ, and the power reserve that tourbillon cage designers must resolve.
While production of most components of a tourbillon cage can today be industrialized, its assembly requires the expertise of experienced watchmakers. A tourbillon cage comprises between fifty and eighty components of very small size, assembled within an extremely limited volume.