Movement (clockwork)
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In horology
Horology
Horology is the art or science of measuring time. Clocks, watches, clockwork, sundials, clepsydras, timers, time recorders and marine chronometers are all examples of instruments used to measure time.People interested in horology are called horologists...

, a movement is the internal mechanism of a clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

 or watch
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

, as opposed to the case, which encloses and protects the movement, and the face
Clock face
A clock face is the part of an analog clock that displays the time through the use of a fixed numbered dial or dials and moving hands. In its most basic form, recognized universally throughout the world, the dial is numbered 1–12 indicating the hours in a 12-hour cycle, and a short hour hand...

which displays the time. The term originated with mechanical timepieces, whose movements are made of many moving parts. It is less frequently applied to modern electronic or quartz
Quartz clock
A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...

 timepieces, where the word module is often used instead.

In modern mass produced clocks and watches, the same movement is often put into many different styles of case. When buying a quality pocketwatch from the mid-19th to the mid-20th century, for example, the customer would separately pick out the movement and the case of his choice, and the movement would be installed in the case for him. Mechanical movements get dirty and the lubricants dry up, so they must periodically be disassembled, cleaned, and lubricated. One source recommends servicing intervals of: 3–5 years for watches, 15–20 years for grandfather clocks, 10–15 years for wall or mantel clock
Mantel clock
Mantel clocks — or shelf clocks — are relatively small house clocks traditionally placed on the shelf, or mantel, above the fireplace. The form, first developed in France in the 1750s, can be distinguished from earlier chamber clocks of similar size due to a lack of carrying handles.These clocks...

s, 15–20 years for anniversary clocks, and 7 years for cuckoo clock
Cuckoo clock
A cuckoo clock is a clock, typically pendulum-regulated, that strikes the hours with a sound like a common cuckoo's call and typically has a mechanical cuckoo that emerges with each note...

s, with the longer intervals applying to antique timepieces.

Mechanical movements

Mechanical movement, Deutsches Museum, München

A mechanical movement contains all the moving parts of a watch
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

 or clock
Clock
A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

 except the hands, and in the case of pendulum clock
Pendulum clock
A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a resonant device; it swings back and forth in a precise time interval dependent on its length, and resists swinging at other rates...

s, the pendulum
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

 and driving weights. The movement is made up of these parts:

Power source: Either a mainspring
Mainspring
A mainspring is a spiral torsion spring of metal ribbon that is the power source in mechanical watches and some clocks. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it...

, or a weight suspended from a cord wrapped around a pulley
Pulley
A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...

. The mainspring or pulley has a mechanism to allow it to be wound up, which includes a ratchet
Ratchet (device)
A ratchet is a device that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. Because most socket wrenches today use ratcheting handles, the term "ratchet" alone is often used to refer to a ratcheting wrench, and the terms "ratchet"...

 to prevent it from unwinding. The barrel or pulley has gear teeth on it which drives the center wheel.
Wheel train
Wheel train (horology)
In horology, a wheel train is the gear train of a mechanical watch or clock. Although the term is used for other types of gear trains, the long history of mechanical timepieces has created a traditional terminology for their gear trains which is not used in other applications of gears.Watch...

: A gear train
Gear train
A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...

 that transmits the force of the power source to the escapement. Large gears known as wheels mesh with small gears known as pinion
Pinion
A pinion is a round gear used in several applications:*usually the smallest gear in a gear drive train, although in the case of John Blenkinsop's Salamanca, the pinion was rather large...

s. 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.
Escapement
Escapement
In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

: 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
Pendulum
A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

 or a balance wheel
Balance wheel
The balance wheel is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral spring, the balance spring or hairspring...

. 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
Bob (physics)
A bob is the weight on the end of a pendulum most commonly, but not exclusively, found in pendulum clocks.- Reason for use :Although a pendulum can theoretically be any shape, any rigid object swinging on a pivot, clock pendulums are usually made of a weight or bob attached to the bottom end of a...

, while balance wheels have a regulator lever on the balance spring
Balance spring
A balance spring, or hairspring, is a part used in mechanical timepieces. The balance spring, attached to the balance wheel, controls the speed at which the wheels of the timepiece turn, and thus the rate of movement of the hands...

.

Types of movements

Watch movements come in various shapes to fit different case styles, such as round, tonneau, rectangular, rectangular with cut corners, oval and baguette, and are measured in ligne
Ligne
The ligne is a unit of length that was in use prior to the French adoption of the metric system in the late 18th century, and is still used by French and Swiss wristwatch makers to measure the size of a watch movement.- Watchmakers' use :There are 12 lignes to one French inch...

s
, or in millimetres. Each specific watch movement is called a caliber
Caliber
In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....

. The movement parts are separated into two main categories: those belonging to the ébauche
Ébauche
Ébauche is a term used in art to denote the first preliminary underpainting or quick sketch in oils for an oil painting. One early criticism of Impressionist painting was that its practitioners sought to elevate the status of the ébauche to the level of finished painting...

s
and those belonging to the assortments.

In watch movements the wheels and other moving parts are mounted between two plates, which are held a small distance apart with pillars to make a rigid framework for the movement. One of these plates, the front plate just behind the face, is always circular, or the same shape and dimensions as the movement. The back plate had various shapes:
Full plate movement: In this design, used in the earliest pocketwatches until the 18th century, the back plate was also circular. All the parts of the watch were mounted between the two plates except the balance wheel, which was mounted on the outside of the back plate, held by a bracket called the balance cock.
Three-quarter plate movement: In the 18th century, to make movements thinner, part of the back plate was cut away to make room for the balance and balance cock.
Bridge movement: In modern watch movements, the back plate is replaced with a series of plates or bars, called bridges. This makes servicing the movement easier, since individual bridges and the wheels they support can be removed and installed without disturbing the rest of the movement. The first bridge movements, in Swiss pocketwatches from around 1900, had three parallel bar bridges to support the three wheels of the going train. This style is called a three finger or Geneva movement.

Mechanical watch movements are also classified as manual or automatic:
Manual or hand winding: In this type the wearer must turn the crown periodically, often daily, in order to wind the mainspring, storing energy to run the watch until the next winding.
Automatic
Automatic watch
An automatic or self-winding watch is a mechanical watch, whose mainspring is wound automatically by the natural motion of the wearer's arm, providing energy to run the watch, to make it unnecessary to manually wind the watch. A watch which is not self-winding is called a manual watch...

or self winding: In this type, used in most mechanical watches sold today, the mainspring is automatically wound by the natural motions of the wearer's wrist while it is being worn, eliminating the need for manual winding.

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