Mechanical watches have no battery, microchip, or circuitry.
Watch parts are machined to near perfection at microscopic sizes and tolerances and can produce accuracy within 2 - 3 seconds per day.
Power is stored in the main spring and released in reliable increments by the oscillating escapement assembly.
The connected gears between the mainspring and escapement (the “wheel train”) turn at various speeds, allowing the watch to “tell time”.
Time setting & winding
The crown is pulled out to set the time and pushed in to wind the watch.
In each mode (pulled out or pushed in) different gear sets are engaged.
Crown & winding stem
The yoke moves the sliding pinion and has a spring for outward tension.
The sliding pinion has teeth on both sides to engage either setting or winding gear sets.
For setting time, the setting lever presses against the yoke to move it inwards. For winding, the setting lever releases the yoke outwards.
The setting jumper holds the mechanism in place, and produces a characteristic “click” when switching modes.
Mainspring & barrel
The mainspring is a spiral spring made of steel ribbon.
It is fitted inside of the mainspring barrel.
Click & ratchet wheel
The click limits ratchet wheel rotation to one direction so the mainspring cannot unwind.
The toothed gears (cannon pinion, hour wheel) that hold time-keeping hands are friction coupled such that with adequate force they can be moved for time setting without disturbing the underlying wheel train gears that continuously drive them.
The mainspring is connected to the winding pinion at the center and the mainspring barrel on the outside, but the pinion and barrel move independently.
Winding force comes through the pinion, and the click ensures that the spring stays in place so spring power goes out via barrel rotation.
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The wheel train connects the mainspring and escapement, and drives time-keeping hands and associated wheels.
The center wheel rotates once per hour.
The fourth wheel rotates once per minute and holds the second hand.
The axle of each wheel rests in a synthetic jewel bearing. The near- frictionless jewels allow the mechanics to work as long as several decades in some instances.
Escapement & balance wheel
The escapement (escape wheel and pallet fork) and balance wheel work together to regulate the release of mainspring power in precisely timed increments.
The balance wheel (most fragile part of the watch) is supported by a
shock-absorbing mounting system complete with a jewel bearing and capstone which protects the wheel if the watch is dropped, etc.
The regulator adjusts the active length of the hairspring which adjusts the speed of the balance wheel oscillation.
Curb pins hold the hairspring in place.
The impulse pin on the balance wheel knocks into the pallet fork (1), releasing the escape wheel so it can rotate (2).
The escape wheel’s teeth (driven by mainspring power) are specially designed to give the pallet fork a “push” (3) which in turn pushes the impulse pin (4), sending the balance wheel into another swing.
Ticking & beats
The pallets catch the teeth of the escape wheel, making a "ticking" noise.
Each incremental escape wheel rotation is called a beat. A common watch beat rate is 21,600 BPH (or “beats per hour”), which is six beats per second.
The motion works powers the watch’s hands, translating wheel train rotation into readable time.
The hour wheel rotates once per 12 hours.
The seconds hand (shown in the introductory illustration) is powered by the fourth wheel in this particular watch movement.
Flow of power
The cannon pinion holds and powers the minute hand.
The slower-rotating hour wheel and hour hand is powered by the cannon pinion through the speed-reducing minute wheel.
The barrel bridge holds the mainspring and barrel, and associated parts.
Train wheel bridge
The train wheel bridge holds wheel train parts and other assorted elements.
The pallet bridge holds balance fork. The shape of the pallet bridge limits pallet fork travel as the fork moves back and forth with the balance wheel.
The balance bridge holds the balance wheel and regulator.
The main plate serves as a base to mount all the movement’s parts.
The full, expanded model
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- Dan, D. (2016). Keyless work fix [Part 1: 6497]. Replica-watch.info. Retrieved 4 November 2016, from https://www.replica-watch.info/vb/showthread.php/135676-Keyless-work-fix-Part-1-6497
- How To Mechanical Watch Movement. (2016). Horologyzone.com. Retrieved 4 November 2016, from http://horologyzone.com/watch/watch-school/watch-movement-disassembly.html
- How To Remove A 6497 or 28xx Watch Movement (Decase A Movement). (2016). YouTube. Retrieved 4 November 2016, from https://www.youtube.com/watch?annotation_id=annotation_19496675&feature=iv&list=PLuy167aHw0eFVFUEfVLSal2t4PHjuTvmv&src_vid=jFV1N5FKkT0&v=65nta3Ry4qQ
- Mechanical watch. (2016). En.wikipedia.org. Retrieved 4 November 2016, from https://en.wikipedia.org/wiki/Mechanical_watch
- Odets, W. (2007). Illustrated Glossary of Watch Parts (1st ed.). TimeZone Watch School. Retrieved from http://people.timezone.com/mdisher/WatchSchool/pdfs/TZIllustratedGlossary.pdf
- Technical Communication ETA 6497-1. (2016) (1st ed.). Retrieved from https://secure.eta.ch/CSP/DesktopModules/ViewDoc.aspx?tabindex=2&tabid=28&DocId=204&DocType=DT
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