Sartory Billard began developing a highly complex hour and minute jump tourbillon watch a year ago and is currently in the advanced stages of the design process, with both the dial and movement almost completed.
To recap: After designing a series of remarkably successful, fully customizable timepieces, namely the SB04 automatic watch, the SB05 hand-wound watch, and the SB07 sports watch, Armand Billard decided it was time to venture into the realm of complications. Late last year, the brand introduced its first tourbillon watch – the SB06 Flying Tourbillon, a project born at the request of Cronotempvs, a private collectors club in Spain. For the SB08, Armand opted for a digital hour and minute complication, a decision aimed at freeing up a significant area of the dial for customization.
Watches with jumping indicators already pose a great challenge to the watchmaker, as the discs are much heavier than traditional hands, which not only affects the power reserve, but also leads to a drop in amplitude, especially when all three discs advance at the same time at the top of the hour. However, the SB08 is also a tourbillon, which makes things much more complicated when it comes to energy management. In fact, this is the first tourbillon watch with a jumping hour and minute display. To do this, Armand enlisted the help of movement developer Mathieu Cleguer.
In Part 1 of the series we ran, Mathieu had designed the movement so that the crown wheel was positioned at 12 o’clock, driving two parallel barrels. The gear train drives a remontoir that releases energy to power the jump of at least one disk per minute and power the rotation of the tourbillon. The disc of the minute unit is mounted directly on the pivot point of the remontoir wheel and triggers the jump of the minute, ten and hour discs one after the other through a system of Maltese crosses.
Since then, the entire design has evolved significantly, with notable refinements and developments, particularly in the areas of hand creation and bridge design.
Fundamental changes in construction
Originally, the jumping display, which consists of Maltese crosses and three disks, was intended to be placed on the dial side of the base plate. However, to make assembly and adjustment easier, Mathieu decided to separate the chronometric part of the movement from the jump display. The jumping display is mounted on a separate plate on the dial side of the movement and is connected to the base plate via a pinion, which directly drives the minute disc.
Originally the crown was supposed to be positioned at 12 o’clock for symmetry reasons. However, the team later decided to move the crown to the traditional three o’clock position. The decisive factor here was the desire to add a touch of classicism to the largely contemporary design and to ensure ergonomic winding. Additionally, this also ensures that the winding shaft is closer to the minute disc (more on this later).
However, the process of moving the crown to three proved far easier said than done, requiring numerous revisions to arrive at the final design. First, Mathieu decided to basically rotate the movement by 90° so that the barrels now take up the left half of the movement. At the same time, he had to make adjustments to the arrangement of the gear train to visually optimize the available space now in the lower right quadrant of the movement. In the original design (1A), he moved the tourbillon from the edge inward and added two coaxial intermediate wheels in front of the remontoir wheel to fill the empty space in the lower right quadrant.
He also redesigned the remontoir anchor and fork so that they were further inside the movement rather than on the edge. However, in this design the coaxial wheels overlap the barrel and limit the height of the remontoir mechanism on the nearest axle. This was remedied in the next two designs (1B and 1C), where he centralized the second and third wheels in the gear train.
However, a major challenge arose when designing the time setting mechanism. On a clock with conventional hands, the time can be set when the sliding pinion comes into contact with the minute wheel in the clockwork via an intermediate wheel. However, in this case, the intermediate wheel must be connected to the pinion of the minute disk that is too far away. In order to cover the distance, a long and intricate gear train had to be introduced.
In addition, the remontoir must be isolated during time adjustment to ensure precise adjustment. This means that the minute disc can no longer be attached to the pivot point of the remontoir wheel. At the same time, both Armand and Mathieu felt that vertical symmetry was more visually convincing than horizontal, and they returned to their starting point.
In the final design, the barrels are located at the top of the movement. They are mounted from the bridge side with the lid facing up with the ratchet wheels underneath. This is why the crown wheel is located on the dial side of the movement.
The remontoir is still on the seconds wheel (third wheel in the gear train). The outer curve of the remontoir spring is attached to a bolt and is attached to a movable bolt holder on the ratchet wheel. The bolt holder can be moved laterally to adjust the stiffness of the spring. The spring is wound up by the gear train, but is only released every minute by advancing the ratchet wheel.
The stop wheel is unlocked using a pallet stone on an anchor that is connected to a fork. The movement of the fork is in turn controlled by a Reuleaux triangle located on the fifth wheel coupling. Thus, for each 60° rotation of the Reuleaux triangle, the armature unlocks a tooth of the stop wheel and releases energy to the rest of the gear train until the second pallet of stones prevents the stop wheel from advancing further, tensioning the remontoir spring once again. Under the fourth wheel there are two pinions on the same axle – one pinion is attached to the rod of the ratchet wheel, while the second pinion is rotatably mounted.
The biggest challenge, apart from the intricacies of the complication itself, lay in the design of the keyless movements. Due to the unconventional display driven by the remontoir, the design of the keyless movements, particularly the time setting mechanism, proved to be anything but intuitive. The team decided that the hours and minutes would be set in the first position and the barrels would be wound with the crown in the neutral position.
Mathieu came up with an ingenious design that isolates the remontoir during the time setting. The time setting mechanism has a rocker that carries a set of intermediate sprockets – two at one end and a pair of superimposed sprockets at the other end. During normal operation of the watch, when the crown is in the neutral position, the stacked pinions, which are attached to a rod by a pin, mesh with the two pinions under the remontoir wheel and synchronize them to form the pinion of the to drive minute disk.
However, when the crown is pulled out to the second position to set the time, the rocker rotates and the stacked sprockets disengage from the sprockets on the remontoir bar, allowing them to rotate independently. At the same time, the other two pinions are positioned at the free end of the rocker so that they are driven by a third pinion, which in turn is driven by the intermediate winding wheel via a series of gears. The outer pinion drives the bottom pinion of the remontoir bar, which in turn drives the pinion of the minute disc, effectively isolating the remontoir.
The jump time display itself has also been refined. The minute disc’s pinion is driven by the remontoir wheel’s pinion, causing it to jump forward with each minute. Every 10 minutes, the finger moves a six-armed Maltese cross on the disc, which is attached to a 60-minute intermediate wheel. It drives a smaller idler wheel at a ratio of 2:1, and attached to this wheel is a cam which carries three equally spaced raised hooks which act as fingers and advance the minute tens disc in increments. The minute tens disc is equipped with 12 branches, which is necessary for controlled intermittent movement.
As the Maltese Cross makes one full revolution in one hour, a finger piece advances a 12-branched Maltese Cross to which the hour disc is attached. The Hour Maltese Cross now features a skeletonized design to reduce inertia.
Bridge design and machining
The bridge layout was completely revised, resulting in a much more distinctive and lively movement. The new design is intended to highlight various finishing techniques and make as many components visible as possible. The base plate is finished with glaze, while the recesses are decorated with perlage. The barrels are supported by a bat-shaped bridge accented by a raised rim that is straight grained on the top and polished and beveled on the outer edges. However, its recesses are matted. It features large jewels set in deep, polished depressions.
The seconds wheel is supported by a V-shaped sapphire bridge, while the entire remontoir mechanism is exposed under a larger sapphire bridge. Additionally, this larger bridge features an opening that allows a clear view of the Reuleaux Triangle in action. Of note, all of the exposed wheels in the gear train, as well as the Remontoir stop wheel, have polished and beveled spokes with sharp internal angles. Finally, a black polished bridge with a complicated shape, suitable for a total of nine sharp internal angles, supports the idler gear and pinions in the keyless works on the left side.
The movement was designed from the start with the opening of the jumping indicator positioned at six o’clock on the dial, leaving the rest of the dial free for embellishments. However, Armand decided to design a different version of the dial for those looking for a touch of French flair. It features a cutout that resembles the shape of a keyhole, allowing a glimpse into the inner workings of the display mechanism. It allows a clearer view of the hour disc’s jumping movement as the central hub is exposed. Additionally, the skeletonized Maltese cross can be seen behind the hour hub, engaging a finger piece on the right side.
A nuanced yet impactful element that really elevated the dial’s design was the addition of an elliptical metal rim. This subtly places emphasis on the digital display, contributing to a more refined look overall.
Armand and his team are moving on to the next phase of development, where they will consult with movement manufacturers and specialists. Here too, they remain open to feedback and new perspectives. For subscription series inquiries, please contact Sartory Billard via the official website.
