Thursday, 26 March 2015

The Automatic Watch



In this post, I am writing about automatic movements. My main focus is on the movements that HMT used, of them 8205 and 6501 are kept under the spotlight. I am also posting the Images of the 6501 movement that i recently serviced. And at last there will be a Close-up Video of both the movements.

So What Does The Automatic Movement Mean?
An automatic or self-winding watch is a mechanical watch in which the mainspring is wound automatically as a result of natural motion of the wearer's arm, to provide energy to run the watch, making manual winding unnecessary. A watch which is neither self-winding nor electrically driven is called a manual-wind or hand-wound watch. Majority of the mechanical watches sold today are self-winding.
The most important part of an automatic movement is the Rotor or the oscillating weight.

Rotor of  HMT Cal. 6501

The Rotor And The Automatic Winding
The rotor has a ball bearing in the center and a wheel attached to the base. Due to the movement of the wearer's wrist, the rotor rotates on its axis and with it, rotates the wheel. The wheel is attached to several reduction wheels so that the torque becomes enough to wind the mainspring. There are also mechanisms to make the motion uni-directional , as the mainspring winds in only one direction.

The Problem That Automatic Winding Offers :
If the rotor has been rotating and the spring if fully wound, then if the rotor moves more, the Main Spring Could Break. So, this problem needs to be solved and the solution is as follows.

The Slipping Spring Or 'BRIDLE'
The 'slipping mainspring' device was patented by Adrien Philippe, one of the founders of Patek Philippe, in 1863, long before self-winding watches. It was invented to allow simultaneous winding of two mainspring barrels. In an ordinary manual-wind watch's mainspring barrel, the outer end of the spiral mainspring is attached to the inside of the barrel. In the slipping barrel, the mainspring is attached to a circular steel expansion spring, often called the 'bridle', which presses against the inside wall of the barrel, which has serrations or notches to hold it.
As long as the mainspring is less than fully wound, the bridle holds the mainspring by friction to the barrel wall, allowing the mainspring to be wound. When the mainspring reaches full wind, its force is stronger than the bridle spring, and further winding pulls the bridle loose from the notches and it simply slides along the wall, preventing the mainspring from being wound further. The bridle must grip the barrel wall with just the right force to allow the mainspring to wind fully but not overwind (which may result in it's breakage). If it grips too loosely, the bridle will begin to slip before the mainspring is fully wound, a defect known as 'mainspring creep' which results in a shortened reserve power time.
A further advantage of this device is that the mainspring cannot be broken by excessive manual winding. This feature was often advertised by watch companies as "unbreakable mainspring" or "nonbreakable mainspring".

The HMT Cal. 6501

Sweep second
Day: set by changing 20:30-24h
Date: quickset 


10.5''', Mounting Diameter = 23.3mm, Outer Diameter = 23.75mm
Height = 5.3mm
(ball bearing +0.2mm)
F= 2.0mm
T= 2.3mm
21 jewels
Frequency = 21600 beats per hour
Power reserve = 36h

Stem : Citizen 065-107


1.50 x 1.00 x 0.17mm

Redesigned Citizen 6501 with quickset date
The official calibre designation is not known, but after the reference number of the watch likely the Citizen number was retained.

Example, year: signature; shock device
ca. 1980: U; Parashock (Citizen)

Images Of Service That Was Done By Me

Miyota Cal. 8205 (HMT Cal. 8205)
Sweep second
Day: quickset, 2 languages 
Date: quickset

11.5''', Mounting Diameter = 25.6mm, Outer Diameter = 26.0mm
Height= 5.2mm
F= 1.9mm
T= 2.3mm
With rotor screw and dial spacer:
Mounting Diameter = 28.55mm, Outer Diameter = 29.2mm
Height= 5.67mm
F= 2.1mm (rest to dial side)
T= 2.5mm
21 jewels
Frequency = 21600 beats per hour
power reserve 43h

Balance staff 
Citizen 039-1020
balance with hairspring

Stem Citizen 065-212

Citizen 001-8700
barrel complete


1.52 x 1.00 x 0.17mm
Some full forms

I thought that there maybe a few terms in the movement data that a newbie may not understand so here are a two of them which I believe are the only ones a new person may not understand. If you think that here are any other terms you do not understand or have any doubts please feel free to contact me or Vardhan

F mounting height, distance between dial plane and mounting flange.

T stem height, distance between dial plane and stem center


o0o0o0o0o0 Happy Horology 0o0o0o0o0o

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