balance paired with a differential.
“The movement development went pretty smoothly, even though it took over
two years, but that’s because we had already spent three years experimenting on
the double escapement movement with Legacy Machine No.2 and conical gears
on HM6. If that had not been the case, I cannot even imagine how many years
this project would have taken,” Busser adds.
The unusual case, on the other hand, did threaten to scuttle the entire
HM9 entirely.
“The two “teardrop” sapphire domes on the case nearly killed the whole
project a few months before launch date. It was terrifying.” Busser admits. “The
sapphire manufacturer had a rejection rate of more than seventy-five percent
on each piece, after having spent sixty to eighty hours machining and polishing
them. Finally we managed to get some pieces trickling out, but production is
therefore not at all where we were expecting.”
He adds that initially all MB&F case makers turned down the HM9 project,
calling it either too difficult or impossible. “Finally a small and young
HM9 Road-Edition Top View
manufacturer took on the project – he sort of regretted it later on, as the quality
control rejection rate is more than fifty percent,” he notes.
HIGH-END CHRONOMETRY
Double escapements are rare in watchmaking, in part because the watchmaker
requires perfectly executed engineering, seamless machining and extremely high
tolerances – especially when creating a differential gearing system.
Unlike other multi-balance movements, the HM9 engine deliberately avoids a
resonance effect (a type of harmonic mind meld among two linked oscillators)
in favor of a system using the two balance wheels to obtain “discrete sets of
chronometric data” translated by the differential to produce one stable averaged
reading. The balances are individually impulsed and separated to ensure that
they beat at their own independent cadences of 2.5Hz (18,000 bph) each.
Echoing earlier MB&F’s Legacy Machines, HM9 utilizes dramatic polished
and curved arms to hold these dual balances. Here their placement is almost as
critical as the aerodynamic design to the HM9’s architecture, though the bridges
are possibly less surprising than they were when we first discovered them in the
earlier MB&F watches. The polished arches also serve to contrast with the finish
of the movement bridges below.
Getting the chronometry perfect is just as important to Busser as the overall
watch design.
“We need to respect our core values,” Busser says. “We are above all engineers
and watchmakers. The wild creativity must not hinder our quality and
performance.”
HM9 Road-Edition Engine
64 | INTERNATIONAL WATCH | WINTER 2019