Andreas Strehler Trans-axial® Remontoir Tourbillon

Independent Swiss master watchmaker Andreas Strehler has developed a new movement which combines his Remontoir d’égalité (constant force) with a Tourbillon.

In Andreas Strehler watches, the energy for operating the movement is stored in twin mainspring barrels. The running down of the two mainsprings is limited by an epicyclical gear. Only the optimal part of each mainspring is used where the power supplied is practically constant.

Even by using the highest-grade lubricants and the tightest tolerances in manufacturing each component, the flow of energy from the mainsprings will be subject to variations. Changes in temperature or in the position of the watch will cause such variations. To filter these variations, Andreas Strehler employs a Remontoir d’égalité or constant force escapement.

In Andres Strehler’s Remontoir d’égalité,t he energy supplied from the twin mainspring barrels through the gear train is accumulated in a spring, acting on a satellite arm held in position by the star wheel (the satellite). One tooth of this star wheel is resting on the palette-stone of the palette arm.

This palette arm constantly moves ahead. Every second, the palette arm releases the star wheel. The star wheel turns by one tooth and the satellite arm jumps ahead by 6°. The satellite wheel then rests again against the palette-stone and the cycle starts anew.

When moving ahead by 6°, the satellite arm recharges the spring which drives the escapement. The amount of energy transferred to the escapement thus is always the same, it is constant. The energy is transferred to the escapement through an axis.

The escapement mounted on this axis is a Tourbillon. The Tourbillon is a special escapement. It is also one of the most complicated components known to watchmaking. In a Tourbillon, the whole escapement including the balance rotates typically once a minute.

The idea behind the Tourbillon is that the balance, despite its name, is never perfectly balanced. This means that it oscillates slightly differently, depending on its position in space.

When the Tourbillon was invented by Abraham Louis Breguet in 1801, men wore pocket watches. A pocket watch is carried vertically, and the balance always oscillates on a horizontal axis. This means that gravity pulls more on any part of the balance which is thicker or heavier.

Andreas Strehler Trans-axial® Remontoir Tourbillon

Now, by rotating the whole escapement and hence the balance once a minute, it did not matter if the balance was slightly imperfect: Gravity would still pull heavier on the thicker part of the balance. But, by its rotation, this effect would even itself out.

The balance would, for one part of the rotation of the Tourbillon, work uphill, so to speak. But for the other part of the rotation of the Tourbillon, it would work downhill (and for the rest of the time in neutral).

Andreas Strehler Trans-axial® Remontoir Tourbillon

In his quest for perfection, Andreas Strehler has designed, constructed and built a movement where internal influences on the already pretty linear power supply from the epicyclically limited twin mainspring barrels is filtered through a Remontoir d’égalité and transferred to a Tourbillon escapement mounted on the same axis to eliminate the influence of gravity on the escapement.

Andreas Strehler Trans-axial® Remontoir Tourbillon

The Trans-axial® Remontoir Tourbillon escapement is hand wound, using Andreas Strehler’s own true conical gear wheels.

Andreas Strehler Trans-axial® Remontoir Tourbillon

To show the power left in the two mainspring barrels, the movement has a power reserve indication using an extremely small differential gear, another speciality of Andreas Strehler.

The Remontoir d’égalitéis mounted on three roller bearings and powers a separate jumping seconds indication. The Tourbillon is held in position by two gold chatons.

Andreas Strehler Trans-axial® Remontoir Tourbillon

Technical details

Trans-axial Remontoir Tourbillon

  • Impulse: Double main spring barrel, energy regulated by a remontoir d’égalité
  • Plates and bridges: Three 18k gold bridges, Central Main Plate and bridges are decorated to the highest standards, edges bevelled and polished by hand, fully decorated movement
  • Escapement: swiss lever escapement designed by Andreas Strehler
  • Regulating system: Free-Sprung balance with Breguet overcoil and eight adjustment screws
  • Frequency: 3 Hz / 21’600 A/h
  • Number of jewels: 37, 3 gold chatons
  • Number of individual parts: 250
  • Size: 32.0 x 30.0 mm
  • Height: 7.01 mm (without Tourbillon)
  • Power reserve: 78 h, limited by a differential stop works
  • Functions: Hour, minute, small jumping second, constant force, Tourbillon, power reserve indication (micro differential gear train)
  • Winding-mechanism: Hand winding with conical gear wheels
  • Speciality: Constant force Tourbillon, Remontoir trans-axial underneath the Tourbillon, special roller bearing for the remontoir.

Arnold & Son Constant Force Tourbillon (Royal Collection)

Swiss luxury watch maker Arnold & Son pushes precision chronometry ever further with the Constant Force Tourbillon, featuring a patented constant force device with 60-second tourbillon and true beat seconds.

The symmetrical movement architecture of the Constant Force Tourbillon movement pays tribute to Arnold & Sons’ historic marine chronometers. At the top, two visible mainspring barrels and the constant force device provide optimal power to the tourbillon at the bottom of the dial.
Arnold and Son Constant Force Tourbillon watchThe Constant Force Tourbillon watch is part of the Royal Collection and, like every other model from Arnold & Son, features an in-house mechanical movement.

John Arnold (1736-1793) was constantly searching for higher precision in his timepieces, as the more accurate the chronometer, the more precise the calculation of longitudinal (east/west) position at sea. Arnold and his son were the first to develop and produce technically superlative (but reasonably priced) marine chronometers in significant quantities.

Constant force is an essential element in the quest for higher precision because it is difficult regulating a consistent output, e.g. isochronal time when the power input from the mainspring is constantly changing.

To maximize power consistency in the Constant Force Tourbillon, Arnold & Son began at the beginning, i.e. the mainspring barrel, as this is the source of the movement’s power. Instead of using just one mainspring barrel, which would produce significantly different amounts of torque between fully wound and nearly empty, the Constant Force Tourbillon has two symmetrical barrels in series, visible dial side at 10:30 and 1:30.

The first mainspring barrel alone powers the gear train, while the second barrel tops up the first whenever its torque output drops below optimal. This ensures that the power to the regulator flows as constantly as possible.

Arnold and Son Constant Force Tourbillon

The Constant Force Tourbillon features a patented constant force mechanism. Instead of power from the mainspring feeding directly to the escapement/tourbillon, it charges a small hairspring which in turn releases a consistent amount of power to the escapement/tourbillon once each second.

The device also drives the true-beat seconds hand (also known as jumping seconds or dead seconds), a highly cherished Arnold & Son complication. When the power from the mainspring drops below that required by the constant force mechanism, the movement stops rather than running at lower precision.

The constant force device rotates once per minute in increments of one second, visually mirroring the rotation of the constantly rotating tourbillon cage. The bridges supporting the constant force regulator and tourbillon are also symmetrical, both horizontally with each other and vertically with the barrel bridges.

While the constant force mechanisms optimize precision with the movement in stable positions, the 60-second tourbillon averages out gravitational errors on the escapement by constantly rotating it through 360°. The difference between the rotating tourbillon and rotating constant force device is that the former turns continually while the latter steps in increments of one second.

Arnold and Son Constant Force Tourbillon watch with red gold case and Anthracite open dial

The Arnold and Son Constant Force Tourbillon watch is a limited edition of 28 timepieces, and is available in a 46 mm 18-carat red gold case with anti-reflective sapphire crystal and sapphire display back for viewing the superbly hand-finished movement.

Technical details

Model: Constant Force Tourbillon, Royal Collection
Limited edition: 28 timepieces
Reference: 1FCAR.B01A.C112C

Calibre: A&S5119, Exclusive Arnold & Son mechanical movement, hand-wound, 39 jewels, diameter 36.8 mm, thickness 6 mm, power reserve 90 h, double barrel, 21,600 vibrations/h
Functions: hours, minutes, true beat seconds, tourbillon, constant force
Movement decoration: nickel-silver and steel movement, palladium treated bridges and NAC grey treated main plate with Haute Horlogerie finishing: hand-chamfered bridges with polished edges and brushed surfaces, screwed gold chatons, screws with bevelled and mirror-polishedheads
Tourbillon cage: mirror-polished with hand-chamfered polishededges and circular satin-finished surfaces

18-carat red gold, diameter 46 mm, cambered sapphire with antireflective coating on both sides, see-through sapphire case back, water-resistant to 30 m

Anthracite open dial

Hand-stitched brown bottier alligator leather with patina