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THE FUSÉE-AND-CHAIN TRANSMISSION

Vital precision

Fusee-and-chain transmission

The fusée-and-chain transmission is one of the most effective complications when it comes to increasing the rate accuracy of a mechanical watch.

The fusee-and-chain transmission

Harnessing the laws of physics

It is one of the tenets of physics that the power generated by the mainspring is high when it is fully tensioned and significantly weaker as it nears the fully unwound state. This can cause rate accuracy fluctuations. The fusée-and-chain transmission works like an infinitely variable gearbox. It equalises the waning force of the mainspring and makes sure that the movement always receives a constant amount of energy. This keeps the watch running at an exact rate.

Visible power transmission

Large openings in the three-quarter plate make it possible to observe the interaction of the numerous individual parts through the sapphire-crystal caseback. When the watch is fully wound, the chain is completely wrapped around the fusée. As the spring relaxes, the entire barrel rotates and winds up the chain. In doing so, it turns the fusée, which transfers the torque to the going train via a drive wheel.

Force equalisation according to the principle of levers

The fusée-and-chain transmission obeys the principle of levers. The fusée is shaped like a cone with a helical groove cut into its lateral surface. With full power, the mainspring barrel tugs at the top of the cone, i.e. at the shorter lever. As the spring loses energy, the chain reels off toward the broader end of the cone: as the radius grows, the lever becomes longer.

A drive with a forward and reverse gear

To guarantee that the watch continues to run even while it is being wound, the fusée accommodates a tiny planetary gear system. It assures that power transmission is not interrupted during the winding process, even though the fusée then rotates against the unwind direction.

The perfect middle

When the mainspring is fully wound, and briefly before the fully unwound state, the fusée-and-chain mechanism reaches its limits. This is because in both cases, the torque delivered by the mainspring fluctuates suddenly and incalculably. To assure the utmost in precision, the power-reserve period is thus limited to the middle torque delivery range, where the energy output declines uniformly and calculably.

Blockage before fully wound state

A blocking mechanism becomes active to bypass the sudden loss of force in the fully wound state. It prevents the mainspring from being fully wound: a rivet (1) in the chain activates a lever system (2) at whose end an arresting tooth (3) pushes into the ratchet wheel (4). This blocks the fusée (5), which is rigidly connected to the ratchet wheel.

Blockage before fully unwound state

A second mechanism prevents the occurrence of the second sudden force-loss range. It stops the movement before the mainspring is fully unwound: the power-reserve wheel (6) is the crucial element here. During the 36-hour power reserve period, it rotates by about 300 degrees.

At the end of this path, the beak of a lever (7) drops into the recess in the power-reserve wheel. Simultaneously, its other end (8) pivots into the range of the blocking finger (9). It is connected with the fourth-wheel arbor and rotates exactly once a minute. After no later than 60 seconds, it contacts the lever and blocks the entire movement.

Complications

Grand complications
Grand complications
Grand complications such as the tourbillon, perpetual calendar, rattrapante chronograph or the minute repeater belong to the top tier of precision watchmaking. Some A. Lange & Söhne watches combine several great complications and sophisticated technical solutions in one single watch.
Outsize date
Outsize date
The A. Lange & Söhne outsize date enables a date display with digits around three times as large as those in watches of comparable dimensions.
Chronograph
Chronograph
Chronographs and their manufacture movements have been flagship products of A. Lange & Söhne since 1999.
Calendar function
Calendar function
Lange models incorporate either annual calendars or perpetual calendars.
Moon-phase display
Moon-phase display
Most of our moon-phase displays reproduce the moon’s orbit with a precision of 99.998 per cent.
Power-reserve indicator
Power-reserve indicator
The UP/DOWN display reminds the owner to rewind the watch before it stops running.
Tourbillon watches
Tourbillon watches
The tourbillon improves the rate accuracy of a mechanical timepiece by overcoming the influence of gravity on the running of a watch.
Zero-reset mechanism
Zero-reset mechanism
With the ZERO-RESET mechanism, the movement stops and the seconds hand jumps to zero when the crown is pulled.
The fusée-and-chain transmission
The fusée-and-chain transmission
The fusée-and-chain transmission is one of the most effective complications when it comes to increasing the rate accuracy of a mechanical watch.
Constant-force escapement
Constant-force escapement
The purpose of a constant-force escapement in a mechanical watch is to provide the escapement with a consistent flow of power, regardless of whether the watch is fully wound or nearly unwound.
Striking mechanisms
Striking mechanisms
Watches with a minute repeater or other striking mechanisms make time audible. Given their horological intricacy, these models are among the most elaborate and rare timepieces in the realm of precision watchmaking.

Explore further

Twofold assembly
Twofold assembly
Be it a simple model or a highly sophisticated timepiece – at A. Lange & Söhne, every movement is assembled twice.
Unforgettable masterpieces
Unforgettable masterpieces
Since 1990, Lange has been creating mechanical works of art that have found permanent places in notable collections and in our memories.
Finishing and engraving
Finishing and engraving
The art of finishing movements ranks high in our manufacture. No matter whether large or infinitesimal, whether clearly visible or hidden, almost every part is decorated by hand. Different techniques are used: every component is assigned its own individual type of finish, the sum total a harmonious overall appearance.

How can we be of service?

Whether you are in search of a specific model, have questions out of interest or need a service request for your timepiece – we are delighted to help you. We are at your service by phone, email or in one of our boutiques.

The A. Lange & Söhne salon in Zurich