HowItWorks
Created Thursday 25 July 2024
Mechanical movements
A mechanical movement contains all the moving parts of a watch or clock except the hands, and in the case of pendulum clocks, the pendulum and driving weights. The movement is made of the following components:
Power source
Either a mainspring, or a weight suspended from a cord wrapped around a pulley. The mainspring or pulley has a mechanism to allow it to be wound up, which includes a ratchet to prevent it from unwinding. The barrel or pulley has gear teeth on it which drives the center wheel.
Wheel train
A wheel train is a gear train that transmits the force of the power source to the escapement. Large gears known as wheels mesh with small gears known as pinions. The wheels in a typical going train are the centre wheel, third wheel, and fourth wheel. A separate set of wheels, the motion work, divides the motion of the minute hand by 12 to move the hour hand and in watches another set, the keyless work, allows the hands to be set.
- First or great wheel attached and ratcheted to the main spring, or cable, barrel. The ratchet allows the main spring or cable barrel to be wound without turning the wheel. In horology jargon the pawl of the ratchet is called "the click". The first wheel turns the pinion of the center wheel.
- Center or second wheel which turns once per hour. Its pinion is turned by the teeth on the mainspring barrel in watches and spring driven clocks, and by the weight pulley in weight driven clocks. Its arbor projects through a hole in the face and drives, via a friction coupling, the cannon pinion, which carries the minute hand. It also drives the pinion of the third wheel. In wristwatches with center seconds (i.e. with the seconds hand pivoted coaxially with the minute and hour hands) this wheel is positioned off center to allow the fourth wheel to be placed at the center of the movement. In this arrangement the wheel is called the second wheel, because it is still the second wheel in the train but no longer at the center of the movement.
- Third wheel which drives the pinion of the fourth wheel. It is called the third wheel because the mainspring barrel is the first wheel and the center wheel is the second wheel in the gear train.
- Fourth wheel which, in clocks and watches with the second hand in a subdial, turns once per minute and the arbor projects through the face and holds the second hand. The fourth wheel also turns the escape wheel pinion. Many clocks don't need this wheel because of their slower-moving escapements; in these the third wheel drives the escape wheel directly.
- In watches with a center second hand, the Fourth wheel is concentric with the Center wheel and drives the second hand through the center of the second wheel.
- Escape wheel which is released one tooth at a time by the escapement, with each swing of the pendulum or balance. The escape wheel keeps the pendulum or balance swinging by giving it a small push each time it moves forward.
Escapement
An escapement is a mechanism that allows the wheel train to advance, or escape a fixed amount with each swing of the balance wheel or pendulum. It consists of a gear called an escape wheel which is released one tooth at a time by a lever that rocks back and forth. Each time the escape wheel moves forward it also gives the pendulum or balance wheel a push to keep it moving.
Oscillator
The timekeeping element, either a pendulum or a balance wheel. It swings back and forth, with a precisely constant time interval between each swing, called the beat. A pendulum movement has a pendulum hangar usually attached to a sturdy support on the back, from which the pendulum is suspended and a fork which gives the pendulum impulses. The oscillator always has some means for adjusting the rate of the clock. Pendulums usually have an adjustment nut under the bob, while balance wheels have a regulator lever on the balance spring.
Balance wheel
Glucydur is the trade name of a metal alloy with a low coefficient of thermal expansion, used for making balance wheels and other parts of mechanical watches.
Glucydur is a beryllium bronze; an alloy of beryllium, copper and iron. In addition to its low coefficient of thermal expansion, its hardness (400 Brinell), nonmagnetizability, and resistance to deformation and damage make it suited for making precision parts that must have high dimensional stability. Glucydur is also resistant to corrosion; it is rather inert chemically.
Motion works
Usualy on the dial side, driven from the crown pinion (minute hand) with a 12:1 reduction drive for the hour wheel.
Wheel Train
Ballance Wheel, Fork & Escapement
THE DETAILS OF THE MECHANISM
That the to and fro action of the escape lever is accomplished with such accuracy and regularity--despite changes in temperature, position of the watch, inertial forces applied by the wearer's movements, and shock--is all in the details of design, construction, and adjustment of the escapement.
The following description of the full escapement references Figures 3, 4, and 5, which are all consistently numbered for any given part. All pivots are drawn in yellow, all jewels in red. (Figure 3 is from the Omega Watch Co.) The 15 tooth, club-foot escape wheel itself can be seen at 5, with its pinion at 6. This pinion is driven by the fourth wheel. The lever (7) carries the pallets and pallet jewels at one end (9 and 10) and the small fork at the other. The two angled projections on the small fork are called horns, the area between the parallel sides of the small fork, the notch.
The balance staff (1, 2, 3, and 4 and also Figure 5) carries three major components. The first is the balance wheel itself (1); the second, the impulse roller (3); and the third, the safety roller (4). The impulse roller carries the impulse pin (3A, also known as the ruby pin or the balance pin) that engages in the notch of the lever and rocks the lever to and fro as the balance wheel oscillates in each direction. The safety roller has a crescent shaped cut-out that the guard pin occupies when the balance is centered on the lever. When the balance is rotated away from center (in either direction), the space provided by the crescent cut-out is not available for the guard pin, and thus the lever cannot move laterally and accidentally release the escape wheel. With the crescent rotated away from center, the guard pin hits the edge of the safety roller, blocking the movement of the guard pin and thus the lever. This is necessary to prevent unwanted release of escape teeth while hand-setting backwards and with shock to the watch.
Balance wheel
Pallet Fork
Cutaway drawing of watch
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