Tourbillon

A tourbillon (English IPAEng|tʊərˈbɪljən, French IPA2|tuʁbijɔ̃, meaning "whirlwind") is an addition to the mechanics of a watch escapement. Invented in 1795 by French watchmaker Abraham-Louis Breguet, a tourbillon counters the effects of gravity by mounting the escapement and balance wheel in a rotating cage, ostensibly in order to negate the effect of gravity when the timepiece (and thus the escapement) is rotated. Originally an attempt to improve accuracy, tourbillons are still included in some expensive modern watches as a novelty and demonstration of watchmaking virtuosity. The mechanism is usually exposed on the watch's face to show it off.

How it works

Gravity was thought to have a very adverse effect on the accuracy of time pieces at the time of the invention of the tourbillon, particularly because pocketwatches were often less accurate than stationary clocks of the same construction. The prevailing theory amongst horologists of the time was that pocket watches suffered from the effects of gravity since they were usually carried in the same pocketed position for most of the day, which was vertical, and then held in a different position while being read. Because the movements of pocket watches and similar pieces were oriented with respect to the cases and the dials, their movements were positioned with the axes of motion perpendicular to their faces. This meant that when the timepiece was placed vertically, the axes of motion of the movements would be parallel to the ground, and thus the force of gravity. In such a position, the force of gravity would affect the motion of parts of the movement differently when the parts were in different positions (i.e., moving with gravity or moving against it), which would cause variations in the rate the movement, which in turn would affect the timepieces' accuracy. If adjusted for one position, the rate would change when the piece was kept in a different position, such as when being held to be read or when placed on a table at night. In a tourbillon, the entire escapement assembly rotates, including the balance wheel, the escape wheel, the hairspring, and the pallet fork, in order to average out the effect of gravity in the different positions. The rate of rotation varies per design but has generally become standardized at one rotation per minute. Most tourbillons use standard swiss lever escapements, but some have a detent escapement, and others contain novel designs, such as the Audemars piguet Millenary for example.

The tourbillon is considered to be one of the most challenging of watch mechanisms to make(cite web |title=The tourbillon |author=Jean-Claude Nicolet |url=http://www.europastar.com/europastar/watch_tech/tourbillon.jsp| accessdate=November 2007)(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 travel clocks (travel clocks of the time were of considerable weight, typically weighing almost 200 pounds).

Modern tourbillon watches

In modern mechanical watch designs, a tourbillon is not required to produce a highly accurate timepiece; there is even debate amongst horologists as to whether tourbillons ever improved the accuracy of mechanical time pieces, even when they were first introduced, or whether the time pieces of the day were inherently inaccurate due to design and manufacturing techniques of the day. Nevertheless, the tourbillon is one of the most valued features of collectors' watches and premium timepieces (Ref. August 2006 WatchTime article "Girard-Perregaux's Tourbillon Icon"), possibly for the same reason that mechanical watches fetch a much higher price than similar quartz watches that are much more accurate. High-quality tourbillon wristwatches, which are usually made by the Swiss luxury watch industry, are very expensive, and typically retail for at least thousands of dollars or euros, with much higher prices in the tens of thousands of dollars/euros being common. A recent renaissance of interest in tourbillons has been met by the industry with increased availability of time pieces bearing the feature, with the result that prices for basic tourbillon models have receded somewhat in recent years (where as previously they were very rare, in either antiques or new merchandise); however, any time piece that has a tourbillon will cost a great deal more than an equivalent piece without the feature.

In recent years, Sea-Gull (Tianjin-Seagull Watch Group Co, Ltd.) has joined the group of (mainly Swiss) 'manufacteurs' who make tourbillon movements. In 2007 Sea-Gull even presented a double tourbillon (in 18K gold) at the annual Swiss watch fair, Baselworld. This indicates, that the old European brands can expect new competition from China also at the high-end. Prices of Sea-Gull's watches have also increased over the past few years as the company is gaining confidence and recognition as a high quality manufacturer. However, Sea-Gull tourbillon watches are still considered reasonably cheap, as they are sold a prices from around 5,000 USD. This should be seen in contrast to the tourbillon movement watches from European watch houses, which cost at least tens of thousands of dollars/euros.

Modern implementations typically allow the tourbillon to be seen through a window in the watch face. In addition to enhancing the charm of the piece, the tourbillon acts as a second hand as it rotates once per minute. (There are many "Tourbillon" fake/replicas of premium brand watches that emulate this feature with the oscillating balance wheel visible through the watch dial; however, these are not tourbillons.)

In the late 20th century, the first research into multi-axis tourbillion movements was done by British clockmakers Anthony Randall and Richard Good, eventually producing two- and three-axis tourbillon movements.

External links

* [http://watch-wiki.de/index.php?title=Tourbillon Watch-Wiki: Tourbillon (de)]
*http://www.p178host.com/gpgallery/Prescher/3t.htm
*http://www.timezone.com