Basic operations of a watch
Dear time aficionados,
For many years I have been trying to explain the basic principles of a mechanical watch.
It is not complete, but I hope it is worth reading.
A constant rate is necessary
Clocks use a pendulum;
Mechanical watches use a balance wheel;
Electronic watches use a tuning fork resonator;
Electric watches use a quartz crystal resonator;
The Atomic clock uses a Caesium atom.
All the above supply a vibration or frequency, to regulate the release of energy at set intervals.
This frequency is measured in Hertz and relates to the time of one complete vibration (one cycle) in a second.
A pendulum takes two seconds to swing from the right to the centre to the left
The balance wheel in a watch can vibrate up to 8 times a second
Quartz crystal vibrates at 32,768 times / second
The caesium atom 9,192,631,830 times per second
The faster the frequency, the more accurate, long term ‘steady time keeping’ is achieved.
What about positional errors?
A clock using a pendulum must be level or it will not have steady time keeping.
The metals used can be affected by temperature, distorting the rate.
A clock which compensates for temperate is called a Regulator.
A watch which compensates for different positions and temperature is called a Chronometer.
Some different timing and testing positions
The chances of your watch or mine containing real jewels, say ruby, sapphire or diamonds INSIDE the movement are slim. Today, synthetic jewels are used.
Jewels serve two functions, relating to friction
1) Separate soft brass (plates) from hard steel (pivots)
2) A reservoir for lubrication
The shape of the top part is cupped, allowing oil to be retained. The inside is hollow so the metal pivots can sit inside.
Two jewels can sit on each other, the top ‘cap’ jewel being held by a spring. If the watch is dropped the cap jewel End stone should absorb the energy so the balance staff (pivot) won’t break or bend.
This is known as Shockproof. Popular styles include Incabloc, Kif and Forster.
So, the more jewels, the better quality the movement; generally.
Jewels are also used to separate metals and for lubrication at the end of the lever (escapement) in the form of rectangular pallets.
The other main type of jewel is the roller jewel, fitted to the balance staff.
WINDING AND SETTING
Today’s modern watch uses winding and setting mechanisms based on pocket watches.
When we make a purchase on the Crown (winder) and pull it out a notch, the watch will engage the hand setting mechanism. Earlier designs used a key, placed on the hand and turned to set the time.
The term ‘overwinding’ is wrong.
A mechanical watch uses a long, thin ribbon of steel, wrapped around a rod and held in a barrel. One end is connected to the barrel (outside) and the other end to the rod (inside). Turn the rod and the ribbon of steel will wind.It will wind until there is no more length of the ribbon left. The ribbon or Mainspring is fully wound and will turn no more. How can you ‘overwind’ it?
If you hold onto the rod the barrel will spin until the mainspring unwinds fully. If you hold onto the barrel, the rod will spin until the mainspring unwinds fully.
Self winding, Automatic watches are fitted with a counterweight, shaped like a half moon. As the wearer moves the counter weight spins, transferring the energy to the winding system.
Power, stored in the mainspring is transmitted to the escapement through the gear train.
The gear train is held in place between two plates of brass. Jewels separate the softer brass plates from the hard steel pivot.
The Hairspring is a very fine ribbon of metal, similar to the mainspring just much finer.
Instead of winding up fully and winding down fully, the hairspring ‘breaths’.
It is fixed at the centre to a rod (Balance staff / pivot)) and a round wheel at the outside (Balance wheel). If you turn the inside balance staff and hold the outside balance wheel, the fine ribbon of metal will wind in and out, the inside balance staff will turn clockwise then anticlockwise, back and forth.
If you hold the balance staff the balance wheel will turn back and forth.
Early balance wheels were made of steel and were subject to temperature changes causing the rate to change thus variations in time keeping.
Later Bi-metal balance wheels were used, containing two dissimilar metals, usuually a brass and steel bond that would allow for temperature variations.
Special metal alloys were invented around 1920 that were not as susceptible to temperature variations. Some examples are Enlinvar, Isoval and Nivarox.
If a watch, particularly the balance wheel has been adjusted in all positions (up to six) and tested in all temperature variations, and passed, it is a certified Chronometer.
The Escapement allows the circular motion of the wheels (gear train) to be transferred to a sideways, reciprocating motion allowing the energy to escape.
The stored energy in the mainspring is transmitted through the gear train (held in position by pivots, supported in the brass plates by jewels). The last wheel (Escape wheel) has hooked teeth.
A Lever escapement is the most common type of escapement
The lever resembles a two pronged pitch fork or Pallet, pivoted in the middle, allowing it to rock (horizontally) back and forth. As it does this, one side of the fork (pallet) locks into a hooked tooth of the Escape wheel, as it arcs the other way, the tooth is released, and the other pallet engages and locks onto a tooth. At the end of the two pallets are Jewels. Like all jewels they separate metal parts (friction) and are oiled (lubrication).
The dropping of the pallets into the hooked teeth gives us our ‘tick-tock’ sound.
Energy stored in the mainspring is transmitted through the gear train. The escapement allows the energy to be released at set intervals.
Each time the lever releases (drops), the last wheel or escape wheel, turns one notch.
The lever’s dropping and rising action is controlled by the balance