MB&F HM9-SV purple

The Crystal Clear of Watchmaking: HM9-SV

Launched in 2018, Horological Machine N°9 – nicknamed HM9 “Flow” – paid homage to the extraordinary designs of the cars and planes of the 1940s and 50s. It featured an unusual case, inspired by the flowing aerodynamic lines of the era.

Despite its striking appearance, MB&F founder Maximilian Büsser described the HM9’s engine as “the most beautiful in-house movement ever created”. What could be more logical than to house it in a transparent sapphire crystal case?

Thus were born the Horological Machine N°9 “Sapphire Vision” – aka HM9-SV.

A sapphire crystal and precious metal shell, curved, domed and precision-assembled in three parts, is rendered water-resistant thanks to the exclusive combination of a patented three-dimensional gasket and a high-tech assembly compound. Two totally independent cantilever-mounted balances transmit data to a differential that converts these two oscillations into a coherent pulse. Ultra-precise bevel gears efficiently transmit the motor’s energy and information over a 90° angle, to display the time on a sapphire crystal dial, graduated with Super-LumiNova.

On the reverse, co-axial propellers are placed under each balance wheel: the two turbines spin freely for our purely visual pleasure, waiting for someone to be willing to start a new type of exploration. After the original HM9 Flow “Air” and “Road” editions conquered land and sky, the HM9-SV takes us into the depths of the ocean – the last realm on Earth still harboring many unexplained secrets. We discover a ship of exploration from Atlantis, powered by a divergent technology both familiar and strange to us.

On the outside, the HM9-SV’s lines follow the layout of the editions designed for road and air. The laws of fluid dynamics remain dominant in the design, even if the aquatic objectives give the HM9-SV a softer approach to the reentrant acute angles and parabolic curves of previous Flow versions. From a technical point of view, dimensions had to be reworked to take into account the particular properties of sapphire glass: although extremely hard, it can undergo significant fractures under pressure, where metal would only deform. The HM9-SV’s softened lines reduce potential areas of mechanical vulnerability – while enhancing the aesthetics of an ocean-going craft.

The HM9 engine follows in the footsteps of the engines of Horological Machines N°4 and N°6, disregarding conventional constructions. The three-dimensional assembly of wheels, gears, plates and bridges produces unexpected shapes to match the dynamic lines of the case, an ensemble animated by mechanical viscera and an endoskeleton within a crystalline body.

A traditional frequency of 2.5 Hz (18,000 A/h) may seem anachronistic in a modern chronometer, but the shock sensitivity associated with reduced speed is offset by the use of two balances instead of one. Statistically, two identical systems produce an average that performs better than a single system.

To further reduce shock sensitivity, the HM9-SV editions feature a new anti-shock system: coil springs placed between the movement and the case. The springs are laser-cut from a solid tube of polished stainless steel, providing excellent elasticity and limiting lateral displacement.

Averaging the time measurement from the HM9 motor’s two balances, a planetary differential, the movement’s gearbox, provides the final display on the perpendicular dial. This complex mechanical computation was partially revealed in the original HM9 Flow, with sapphire crystal domes on each balance wheel and a magnifying glass on the planetary differential, to underline the importance of its chronometric role. In the HM9-SV, the entire motor is visible: you can observe the interaction of components from the barrel to the balance wheels and from the differential to the dial.

New solutions had to be found to unite the sapphire crystal components and form a watertight case. A three-dimensional rubber gasket had already been used in the original HM9 Flow, to ensure watertightness when the three parts of the case were attached. While the 3D gasket remains in the HM9-SV, the sapphire crystals are sealed to the metal frame with a high-tech compound, using an in-house vacuum and high-temperature process. The result is a water-resistance rating of 3ATM (30m), although the joint between the sapphire components and the minimalist gold frame is virtually invisible.

The HM9 Sapphire Vision was initially available in four limited editions of just five: two with rose gold frames, combined with black NAC- or blue PVD-treated motors, and two with white gold frames, with violet PVD- or rose gold-plated motors. In 2023, two new editions join the ranks of HM9 Sapphire Vision: a model with a blue PVD-coated engine and white gold frame, and a green PVD-coated engine framed by a yellow gold frame. These two new editions are limited to five pieces each.

A CLEAR VISION

Corundum, usually called sapphire when it’s a gem, is one of the hardest minerals known to man. Few materials are harder than corundum, notably diamond (crystalline carbon), which scores 10 on the Mohs scale, compared with 9 for corundum. Thanks to their exceptional hardness, sapphire watch glasses are virtually scratch-proof, ensuring unrivalled legibility and material integrity over the long term, not to mention the prestigious dimension lacking in ordinary silicate or transparent polycarbonate glasses – the two most common alternatives to sapphire glasses.

At the same time, sapphire is extremely difficult to machine into complex three-dimensional shapes, a challenge amplified by the low tolerances required in watchmaking. Since its earliest creations, MB&F has been experimenting with ever more sophisticated sapphire crystal components, with prime examples being the HM2 “Sapphire Vision”, the double-arched crystal of the HM4 “Thunderbolt”, the recent HM3 FrogX and the hallucinating body of the HM6 “Alien Nation”.

It takes around 350 hours of meticulous machining and polishing to prepare the lenses for a single HM9-SV case: weeks of work that would be considerably extended were it not for the many years of experience in designing extraordinary sapphire lenses acquired by MB&F since 2005.

FURTHER INFORMATION ON THE HM9 ENGINE

The result of three years of development, the HM9 motor was entirely designed and assembled in-house, thanks to the experience accumulated by MB&F through the realization of 20 different movements to date.

Long-time members of the MB&F Tribe will recognize the mechanical pedigree of the HM9 motor. Although presented in a very different form, the double balance with differential derives from the comparable mechanism of the Legacy Machine N°2. Whereas the LM2 emphasized the purity of design and the hallucinating effect of its suspended oscillators, the HM9 celebrates its expressive design with verve.

Two pendulums in the same movement inevitably raise the question of resonance, the mechanical phenomenon that sustains mutual harmonic excitation between two coupled oscillators. Like the motor of the LM2, that of the Horological Machine N°9 eliminates any resonance effect. The reason it incorporates two balances is to obtain separate chronometric data to be transmitted to a differential in order to produce a stable average display. This objective would not be achieved with two balances oscillating perfectly in phase, producing equivalent chronometric data at all points.

Setting the two balances is a challenge in itself. To regulate a watch with a standard system, the sound emitted by the oscillating balance is used to measure frequency. As the HM9 motor has two balances operating simultaneously, producing two sets of vibrations, the method is not appropriate. When the Horological Machine N°9 was launched in 2018, each example had to be regulated by blocking one balance wheel to adjust the other, and vice versa. When both balances were ready for operation, the adjustment would undergo a slight shift, requiring several cycles of re-locking and re-adjustment before optimal precision was achieved.

Since then, the MB&F team has made considerable progress in regulation techniques, largely thanks to the experience gained in creating the Legacy Machine Thunderdome. The HM9-SV therefore benefits from a few more years of expertise in this field – not extensive in duration, but immeasurable in terms of know-how.