Miyota 6T15

 
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Miyota 6T15

Description

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 34 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!

base place

base place

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.

mounted minute- and center seconds wheel

mounted minute- and center seconds wheel

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.

gear train

gear train

The gear train is a challenge for every watchmaker: No less than seven(!) wheels are all beared under the large three-quarter plate.

side view of the gear train

side view of the gear train

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.

side view of the selfwinding gear train

side view of the selfwinding gear train

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!

gear train bridge with seven wheels

gear train bridge with seven wheels

The crown wheel is riveted onto the gear train bridge, as well, as the click pawl, which blocks the selfwinding transmission wheel.

transmission wheel

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.

Movement without oscillating weight

Movement without oscillating weight

The oscillating weight is ball-beared and engages into the non-ruby-beared transmission wheel.

inside of the oscillating weight

inside of the oscillating weight

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.

calendar mechanism

calendar mechanism

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)

Miyota 6T15: Dial side

Miyota 6T15: Dial side

In the lab

The specimen shown here was gummed and with visible signs of several years of wearing into the lab. It was serviced and made running again and now works with an average amplitude of 175°. Since this value is far below of a new movement, there are no timegrapher values shown here, however, you can be assured, that with an adjustment, they would still be within the manufacturers’ specification of -20 … +40 seconds per day, and that’s really great!

Technical data

Manufacturer:Miyota
Caliber:6T15
Number of jewels:21
Escapement:Pallet lever
Balance types: Nickel anular balance
Shock protection(s): Parashock 2 (Citizen)
Balance bearing / direction hairspring:Clockwise
Moveable stud:yes
Adjust mechanism:Hairspring key
Construction:
  • lever
  • escape wheel, seconds wheel, third wheel, mainspring barrel
  • center minute wheel
  • center second pinion
Construction type:solid construction
Winding mechanism:yoke winding system
Setting lever spring:1 hole(s)
Features:SCI,QG,RDR,AUT
Functions:hour, minute, second, day, selfwinding
A/h:28800
Size:8 3/4''' (measured: 19,75mm)
Inventory number:18023

Usage gallery

Pascal Hilton ladies' watch

Pascal Hilton ladies' watch

This movement with its watch is a kind donation of Katja to the movement archive. Thank you very much!