Accutrons scare me too!
I can change the battery, and I can remove and replace the movement by myself, but to really work on them you need to almost be a neruosurgeon. My watch guy has all the Bulova factory equipment for Accutrons, and their shop was the Buloav approved Accutron Servcie Center for Alberta, but ahy watch that requires a 15X stereo microscope to work on, is out of my league..
Some Accutron trivia.
-The index wheel of a 218 movement is 2.40mm (0.095") in diameter and has 320 teeth, each of which is about 0.01mm high (0.0004") and 0.02mm (0.0008") wide. The index and pawl jewels are perfect little square blocks of synthetic ruby, 0.18mm (0.007") square and 0.06mm (0.002) thick. How these parts were manufactured has remained a closely-guarded secret.
-Each Accutron coil has 8,100 turns of insulated copper wire of 0.015mm diameter (or about 1/2000th of an inch). That equates to about 80 meters (or nearly 90 yards) per coil. The wire is about one-third the thickness of a human hair.
How it works..
- Power from the battery flows through the transistor, and then through both of the driving coils. One of the coils (the one which is attached to the plate holding the transistor and its components) also has a secondary coil built into it. When the fork springs one way, this secondary coil provides a feedback voltage which cause the transistor to almost stop the flow of current in the driving coils, and stop driving the fork. When the fork springs back the other way, this feedback coil generates a "reverse" voltage, which causes the transistor to allow current to flow in the driving coils again. The fluctuating current in the driving coils produces a varying magnetic field, which alternately attracts and repels the tuning fork magnets. Thus it keeps on vibrating. The system is self-regulating. If the watch receives a jolt which adds to the fork vibration, the circuit automatically reduces power to the fork until it reaches the normal amplitude of vibration. The reverse is also true.
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The Index Mechanism:
This mechanism provides the means for converting the vibrations of the tuning fork into rotary motion. Even today, it is considered a truly remarkable engineering accomplishment. Though the dimensions of the working parts are incredibly small, the operation of the index mechanism is elegantly simple, and its robustness and reliability legendary. Neverthless, it is very delicate and requires special handling techniques during servicing and adjustment. The index wheel can be destroyed by simply touching it on its rim. It must be handled by its pinion only.
It consist of two very fine flat springs (or "fingers"), each with a small ruby jewel cemented with epoxy onto one end. One of the springs (the pawl finger) is attached to the body of the watch by a small movable carrier and post. The other (the index finger) is attached to a post mounted on one arm of the tuning fork. The jewels of each finger rest on a special ratchet wheel (the index wheel) which has very small triangular shaped teeth. These teeth are so small, they cannot be seen without the aid of a microscope.The positions of the index and pawl jewels relative to each other is adjusted by moving the pawl jewel carrier. Correct adjustment is necessary to allow for variations in fork amplitude during the life of the battery. This is known as "phasing" the index mechanism, and requires good watchmaking skills, experience on Accutrons, and a good understanding of the operation of the index mechanism to be carried out correctly.
In operation, when the fork moves towards the index wheel, the index jewel pushes the wheel around slightly more than one tooth. The wheel is then locked in place by the pawl jewel, so when the fork and index jewel moves back away, the index wheel stays stationary. This occurs once for every vibration of the fork, or 360 times a second for a 214 or 218 Accutron movement.
Amazing watches....
Cheers
Harold
