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Background of Tourbillon

Mechanics of the Tourbillon
An assembled tourbillon, clearly showing balance wheel, pallet fork and escape wheel.Gravity has a direct effect on the most delicate parts of the escapement, namely pallet fork, balance wheel and hairspring. Most notably the tourbillon's hairspring, which functions as a regulator for the escapement and is thus the most sensitive part to any exterior effects, such as magnetism, shocks, temperature, and inner effects such as pinning positions(inner collet), terminal curve and heavy points on the balance wheel.

Many different tourbillon's inventions have been developed to counteract these problems. Temperature and magnetism have all but been eliminated as problems with new materials. Shocks have much less effect today than at Breguet's time thanks to stronger and more resistive materials. The tourbillon's escapement still gets deregulated at the moment of the shock, but the hairspring does not get as easily deformed from shocks as before.

Gravity comes into play on the remaining effects, one of them is easily taken away, namely heavy point on the balance wheel. This leaves pinning point and terminal curve. Both of these are what adds a lot of variation to the regulation of a tourbillon watch, depending on how it is assembled and regulated by the tourbillon watchmaker and positioned in the tourbillon watch and later by the owner. As the balance wheel goes from one extreme position to the other in its swing back and forth, the hairsprings coils extend and contract a great deal, leading to problems that are extremely hard to counteract. Some have tried using hair springs that are cylindrical or even spherical instead of flat as is prominent today. Some variations of Breguets overcoil have been developed to counteract the effects of the terminal curve. As for the pinning point, Grossmann, Berthoud, Breguet, Caspari and Leroy[1] tried many different things, but not much was gained.

The biggest obstacle for a tourbillon's watchmaker regulating a tourbillon watch, even today, is getting a similar result from the escapement no matter the position it is kept in. This has been made infinitely easier with accurate timing machines which give instantaneous timing results, where as in Breguet's time all that watchmakers had was a another watch to regulate from, so results were not very exact and it could take weeks to get them. Effects of gravity on an escapement can have quite significant effects with slight variations of position, even if a pocketwatch was most of the time in a breast pocket, the exact position could still vary over 45°. A tourbillon quite neatly takes away this problem. The tourbillon's watchmaker now only needs to regulate for 3 different positions, instead of 6 like before. Those are two horizontal positions, dial up and down, and four vertical positions, crown at 12, 3, 6 and 9 o'clock.

A tourbillon most often makes one complete revolution per minute, which has no effect in the two horizontal positions, but makes all the difference in the 4 vertical positions, since even if a tourbillon's watch is stationary in a random vertical position, the tourbillon makes the escapement spin around its own axis, effectively cancelling out the effects of gravity of each of the 4 generalized positions. Even today with new materials and improved theories, is it nearly impossible to regulate a watch so it keeps the same time in all positions. A tourbillon allows watchmakers today to obtain results that are better than normal mechanical watches. Although, this is still immensely inferior to quartz, which normally vary 3 seconds per month, where a good mechanical tourbillon watch keeps 3 seconds per day.

Mechanical tourbillon watches today are mostly sold to buyers who value craftsmanship and aesthetics over very accurate timing. Most tourbillons use standard swiss lever escapements, but some have a detent escapement.

The tourbillon is considered to be one of the most challenging of watch mechanisms to make (although technically not a complication itself) and is valued for its engineering and design principles.