MB&F debuts Legacy Machine Split Escapement

Nov 19, 2017

The one technical constant that defines every single watch in the MB&F Legacy Machine collection is that the suspended balance wheel remains literally and metaphorically above everything else. In the Legacy Machine Split Escapement, this feature is raised to another level of achievement

Just below the highest point of the domed dial crystal, the balance of LM SE beats at a sedate, traditional 2.5Hz / 18,000bph. What is rather less traditional is its construction. Unlike most of the other suspended balances in the Legacy Machine collection – indeed, unlike any other balance outside of MB&F – the balance of LM Split Escapement seems to oscillate on its own, without any visible intake of energy. The essential remaining parts of the escapement, which provide the driving impulse – anchor and escape wheel – are concealed on the opposite side of the movement, almost 12 mm below; hence the name ‘Split Escapement’.

Under the balance, the triple-dial design of LM SE gives the time at 12 o’clock, the power reserve indication at 4 o’clock, and the date at 8 o’clock. The date can be quickly and easily adjusted thanks to a push-button on the side of the case, next to the date dial.

Other design features are natural evolutions of those found in previous Legacy Machines, such as the organically arched balance bridge found in the LM Perpetual. More visibly, LM SE features the micro-textured “frosted” finish that is so closely associated with antique pocket watches of the 18th and 19th century; this was presented by MB&F for the first time in the LM 101 ‘Frost’ editions.

Antique watches featuring a frosted finish used acid baths to achieve this effect, but modern methods of replicating a frosted finish involves manually burnishing a metal surface with a wire brush. LM Split Escapement is a celebration of this technique, which is executed completely by hand for all 72 pieces.

The full beauty of frosting is brought out in Legacy Machine Split Escapement, with four launch editions in white gold. Each edition, limited to 18 pieces, is distinguished by frosting and movement finish of a different shade, which allows LM SE to embody varying aspects of its personality: Blue frosted finish paired with rhodium-plated movement for the most classically elegant version; Ruthenium frosting with similarly darkened movement evoking new-millennial functionality and putting the focus on the white lacquer dials; Red gold frosting and movement conveying warmth and accessibility, its subtle roseate sheen emphasising the intense hue of the blued hands; and Yellow-gold frosting and movement finish: the strongest aesthetic affinity with the era inspiring the Legacy Machine collection, an era that defined the precepts of modern watchmaking.

Technical challenges
In watchmaking parlance, the escapement is the set of components that allows the stored energy of the mainspring to escape in a series of regular controlled impulses instead of unwinding all at once. In its most common configuration, it consists of the balance assembly, anchor, and escape wheel, with horological tradition dictating that these components be as close to each other as possible to minimise external disturbing influences. In this particular area of horology, which is rarely challenged, MB&F is raising the bar.

While the balance of LM Split Escapement beats just under the dial-side dome of sapphire crystal, its impulse jewel, anchor, and escape wheel are on the other side of the movement – visible through the transparent case back. This necessitates an unusually long balance arbour, which runs through the centre of the movement – a true milestone of micro-mechanical and manufacturing technique.

The distance between the balance wheel and the impulse jewel is a full 11.78 mm, the length of the arbour that traverses the movement and projects through the dial to support the oscillator. A longer arbour increases the likelihood of disrupting influences on the oscillator, as well as the potential distorting effects of a long axle under continuous torsion. The inertia of the balance and the rigidity of the arbour are key factors in this delicate equation, and the LM SE engine is precisely engineered to ensure its chronometric integrity.

In the Split Escapement, stability of construction becomes exponentially more important than is usual, which significantly restricts the margin of dimensional error during the manufacturing process. In addressing this, the balance arbour is fitted at both ends with anti-shock jewel bearings, and the bridge that holds the anchor and escape wheel is separately fixed for optimal fine adjustment.

Because a longer balance arbour has a higher mass, which potentially detracts from the amount of energy ultimately transmitted to the oscillator, the LM SE engine is driven by two barrels in parallel, which allows up to 72 hours of optimal timekeeping.

MB&F debuted the Legacy Machine collection in 2011, the result of a radical thought experiment by founder Maximilian Büsser. 

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