One of the most interesting and still produced (as of 2018) budget selfwinding movement is the Miyota 6T15 shown here in the “gilt” version. It is a small movement with a diameter of a little less than 20mm (8 3⁄4 lignes) with a very interesting and economic construction, with a “floating” second hand due to the high beat rate of 28800 A/h and with a quickset date mechanism by pulling the crown over the time setting position.
The manufacturer specifications are impressive, the daily rates are with in -20 and +40 seconds per day. For such a tiny and cheap (starting from twenty dollars) movement this is impressive!
You can see on the bas plate, that this is a very well developed and reliable movement. No less than 21 bearing rubies are used here, even the center minute wheel is ruby-beared.
The directly driven center minute wheel is beared under an own bridge. On top of it, there’s the center seconds wheel, which is secured by a spring. This avoids flattering.
The gear train is a challenge for every watchmaker: No less than seven(!) wheels are all beared under the large three-quarter plate.
The lower part of the gear train is the classical one with center seconds wheel, third wheel, which engages into both, the center seconds wheel and into the gears of the minute wheel, and the seconds wheel and steel escape wheel.
The escapement is classical pallet lever escapement, and as balance, a shock protected Glucydur balance is used, which beats with fast 28800 A/h. This causes the center second hand to move very smoothly and also increases the precision.
The upper part is taken from the mainspring barrel and the two reductions wheels of the selfwinding gear train. Please note, that there’s no click here!
The crown wheel is riveted onto the gear train bridge, as well, as the click pawl, which blocks the selfwinding transmission wheel.
The selfwinding transmission wheel has got a clutch, to ensure that the oscillating weight is decoupled, when the movement is manually wound, and it is also decoupled, when the weight turns counter-clockwise, since the Miyota 6T15 is, like most of their movements, unidirectionally winding.
The oscillating weight is ball-beared and engages into the non-ruby-beared transmission wheel.
The calendar mechanism of the Miyota 6T15 uses a transmission wheel and a switching wheel made of plastics. Since the date ring is also made of plastic, this is consistent.
A very good detail is, that the detent spring at 7 o’clock is constructed in a way, that it is held tight on the dial plate and doesn’t fly away easily.
The quickset mechanism works by pulling the crown out over the time setting position. This advances the date ring with the help of the plastic lever at 4 o’clock, which then moves to the left.
When the cover plate is mounted on the dial side, you cannot see much of the calendar mechanism, except for the ratchet and the star wheel, which drives a weekday disc (but only on the caliber 6T51)
In the lab
|Number of jewels:||21|
Nickel anular balance|
Parashock 2 (Citizen)|
|Balance bearing / direction hairspring:||Clockwise|
|Adjust mechanism:||Hairspring key|
|Construction type:||solid construction|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||1 hole(s)|
|Functions:||hour, minute, second, day, selfwinding|
|Size:||8 3/4''' (measured: 19,75mm)|