Tourbillon - Mechanics of The Tourbillon

Mechanics of The Tourbillon

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

Many inventions have been developed to counteract these problems. Temperature and magnetism have 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 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 points on the balance wheel. This leaves pinning point and terminal curve. Both of these add a lot of variation to the regulation of a watch; assembly, regulation adjustments by the watchmaker, positioning in the watch, and later position changes by the owner. As the balance wheel goes from one extreme position to the other in its swing back and forth, the hairspring's coils extend and contract a great deal, leading to problems that are extremely hard to counteract. Some have tried using hairsprings that are cylindrical or even spherical instead of flat as is prominent today. Some variations of Breguet's overcoil have been developed to counteract the effects of the terminal curve. As for the pinning point, Grossmann, Berthoud, Breguet, Caspari and Leroy tried many different possibilities, but not much improvement was gained.

The biggest obstacle for a watchmaker regulating a 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, whereas in Breguet's time all that watchmakers had was 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 pocket watch 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 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 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, it is nearly impossible to regulate a watch so it keeps the same time in all positions. A tourbillon presents today's watchmakers the possibility of higher accuracy than conventional movements.

Mechanical 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. The first production tourbillon mechanism was produced by Breguet for Napoleon in one of his carriage clocks (travel clocks of the time were of considerable weight, typically weighing almost 200 pounds).