Somewhere around 1975, Sonceboz launched a series of simple, Roskopf-inspired pillar movements, some of them with a pallet lever escapement, some of them, like the one here, with a pin lever escapement.
The base plate of this 12 ligne movement, which is stamped with “5400” and thus gives an indication for the caliber number, is well made, nickel plated and equipped with ruby bearings on all important positions.
The gear train reminds of a Roskopf movement, not only because of the missing center minute wheel, but because of the hands, which are driven on the dial side by a gear, which is connected with a slipping clutch to the mainspring barrel. Unlike on a real Roskopf movement, only the cannon pinion engages with the wheel on mainspring barrel, but not the hour wheel, and so a reduction wheel for the hour pinion is required.
The gear train is contemporarily modern, with a second wheel, driven by the mainspring barrel, followed by third wheel, directly driven center seconds wheel and finally the steel escape wheel.
As escapement, the caliber ES 54 uses a pin pallet escapement.
The balance, of course screw-less, beats slowly with 18000 A/h and can be regulated only with the hairspring key directly.
On the specimen shown here, no shock protection of the balance wheel is used, because the slanted arms of the balance should absorb shocks.
This principle was made popular several decades ago by Wyler, under the term “Incaflex”.
On the yet empty dial side, you see besides the yoke winding system how the slipping clutch mounted driving wheel of the mainspring barrel will engage with the cannon pinion.
A bit odd, and probably due to the “magical” number of 17 jewels, which had to be reached, are the two non-detachable cap jewels for the lever axle and the axle of the escape wheel and mainly the bearing ruby for the change wheel, at position 7:30 near the center of the movement.
Technically, a ruby bearing for such a slowly turning wheel is not really useful, but for marketing purposes, of course, it is.
As on a normal lever movement and not like on a Roskopf movement, the hour wheel is driven by an own change wheel and not by the mainspring barrel.
The calendar mechanism is very simple - a 12 teeth switching wheel engages with the 6 teeth star wheel of the hour wheel and thus revolves once a day.
The (in the specimen shown here most probably incomplete) calendar mechanism is secured by a cover, which bears the spring, which is responsible for the snapping of the date ring.
|Size:||12''' (measured: 26,4mm)|
|Number of jewels:||17|
monometallic anular balance (two legs)|
|Balance bearing / direction hairspring:||Clockwise|
|Adjust mechanism:||Hairspring key|
|Construction type:||pillar construction|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||1 hole(s)|