The escapement is composed of an intermediary wheel A, a double Coaxial wheel B composed of escapement pinion C and escapement wheel D, pallet fork E with 3 ruby pallet-stones F, G,H and a balance roller K carrying a ruby impulse stone J and a ruby impulse pin L. The roller is fitted to the sprung balance.
It is essential that a successful escapement for use in a modern watch must transmit energy to the oscillator in both clockwise and anti-clockwise vibrations. In the Coaxial escapement, the clockwise impulse is delivered to the oscillator directly by the escape wheel engaging the balance roller. The anti-clockwise impulse is delivered to the balance roller via the lever. After each impulse, the escape wheel is locked stationary by the lever locking pallets allowing the balance to complete its vibration undisturbed.
( Fig 2.1 )
The balance roller K turning Clockwise to unlock tooth a from entry pallet F.
Clockwise impulse to balance roller K by tooth
b on roller pallet J.
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The balance turning anti-clockwise to unlock tooth
c from exit pallet H.
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Anti-clockwise impulse to balance roller K via tooth d of pinion C and lever impulse stone G.
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3.1 Assembling of the escapement system
The pallet bridge position the coaxial wheel and the pallet fork. To ensure the functioning of the escapement it is necessary to respect the following order of assembly:
1. Position the escape wheel.
2. Position the pallet fork.
3. Position the pallet bridge and check if
the pivots are correctly placed in their beds.
4. To position the pallet bridge, the
screw (4)
must be screwed in first.
5. The second screw fixes the bridge.
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The teeth tips of the escapement wheel have to be lubricated with Molycote DX grease. Also lubricate the teeth tips of the escapement pinion using very little grease.
The pivots of the pallet fork and the coaxial wheel have to be lubricated with Moebius 9010 oil.
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As the table roller is under the pallet fork, the balance must be assembled carefully.
1. Position the complete balance bridge ( with balance ). The bridge is pointing towards the center of the movement.
2. Check the position of the balance. The pivot of the balance-staff must be correctly placed in its bed.
3. Carefully trn the bridge to its normal position.
4. Fix the bridge with its screw.
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The balance bridge must be disassembled by removing the parts in the opposite order procedure 3.3. To avoid any risk of damaging the balance, the bridge has to be turned towards the center of the movement. In this position the bridge may be disassembled without any risk.
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4.1 Balance
The annular balance carries two regulateing screws. If the watch is running slow it can be adjusted by screwing in both screws ( towards the balance center ). Screwing in reduces the moment of inertia which results in higher amplitude. If the watch is running fast it can be adjusted by unscrewing the screws ( away from the balance center).
To Avoid an imbalance, the adjustments must always be made with both screws.
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On a completely rewound movement the amplitude is situated between 260 and 280 degrees
( in horizontal position ).
The rate can be checked with a Witschi Watch Expert or a similar apparatus capable of acoustic measurements. The angle of lift has to be set to 30 degrees.
The acoustic signals of the Coaxial escapement are not as clear as the ones of the traditional escapements. The test apparatus has to be adjusted accordingly.
After 24 hours, the amplitude must be superior to 190 degrees ( in vertical position).
To adjust the rate on an encased movement, a special correction tool has been developed. One complete revolution of both regulating screws of the balance represents a rate correction of 52 seconds. The correction can be read on the scale of the circumference of the tool. One division of the scale represents a rate correction of one second.
One of the regulating screws is between two arms of the annular balance which are marked with dots ( see fig. 4.1 ) making it easy to distinguish one screw from the other during the correction.
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To avoid an imbalance, the adjustments must always be made with both screws.
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Credits: Omega SA