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Lesson 4 -- Structure
& Theory 26 Nov 2006
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There are 4 main parts for a mechanical clock or a mechanical watch.
- Power
- Wheel Train
- Escapement
- Display
In this lesson, we still use the clock as an example,
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| 1. Power |
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The brass gear is called Mainwheel.
The long thin metal strip is called Mainspring.
The amount of energy can be stored mostly depends on the
elasticity (material, e.g. steel) and the effectinve length
of the mainspring.
Most watches have about 50 hours power and some expensive
watches have 8 or more days power.
e.g. Jaeger-LeCoultre Master 8 Days (aboutUS$16,000)
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| 2. Wheel Train |
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The wheel train include gear 2, 3, 4.
There are two functions for the wheel train.
- Transfer the power from the Mainwheel to the Balance Wheel.
When the energy goes through the wheel train, the high torque
form the Mainwheel will become the high speed oscillation
at theBalance Wheel.
- Calculate the time according to the gear ratio between
each wheel.
- Gear 2 -- Minute
- Gear 4 -- Second
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| 3. Escapement |
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Escape wheel, Pallet Fork, Balance Spring and Balance wheel
form the ESCAPEMENT which controls
the time of a clock.
Balance Spring oscillates and Balance Wheel swings as a result
they divide the time.
Anchor and escape wheel control the power release according
to the "divided time".
There are different types of balance wheels, I will introduce
them later.
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| 4. Display |
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Show you the time ! |
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| How to calculate the time with the
gears |
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1 perod = the yellow dot goes from left to right and back
to left.
Frequency = 1 / Time for one period
There are 4 main frequencies for the balance wheel in a watch.
- 18000 per hour
- 21600 per hour
- 28800 per hour
- 36000 per hour
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A : Pallet Fork
Pay attention to the two pins (red rectangles)on
the Pallet Fork in the following movie.
B: Balance wheel
5: Escape wheel
I put some pigments on the parts for movie recording only,
the weight of the pigment will affect the frequency of the
balance spring, as a result, affect the accuracy of the time.
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When the balance wheel swings, it will control the Pallet
Fork to lock or release the escape wheel.
Play back speed is reduced for easy viewing.
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The frequency of the balance wheel can be calculated from the formula:
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For the clock in lesson 3
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Tp(escape wheel)
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15
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Ta(escape wheel)
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8
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Tp(4th)
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60
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Ta(4th)
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6
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Tp(3rd)
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36
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Ta(3rd)
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7
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Tp(2nd)
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70
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Ta(2nd)
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10
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Frequency = ( 70 x 36 x 60 x 15 x 2 ) /
( 7 x 6 x 8 ) = 13500
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The gear ratio for the wheel train should be:
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Because the gear ratio cannot be changed, the accuracy of a clock
or a watch can only be adjusted by the frequency of the balance
wheel.
The frequency of the balance wheel can be changed by adjusting
the effective length of the balance spring.
Longer the effective length = lower the frequency
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Effective lenght of the balance spring = B to
C |
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