I recently acquired a Barr battery clock. It was somewhat dirty and not working. Examination revealed that the roller on the gravity drop arm was contacting the spigot on the pendulum crutch even when in the raised position. There is a small coil spring restraining a moving part of the locking system on the bottom of the drop arm. This seemed to be over-stretched allowing the arm to "sag". Replacement of this spring by a tie of sewing cotton (!) cured the problem and the clock worked. The cotton has since been replaced by a newly wound spring. This seemed to be a critical area and several springs have been tried as I thought some "sag" was probably advantageous here. Not so - the strongest almost immovable spring gave best operation.
However, the clock did only 4 or 6 swings between impulses.
Cleaning is suggested as the answer to all ills so this was done: solvent soaking, ultrasonic clean, pegging out holes and polish pivots.
Still only 6 swings!
Motion work removed leaving only the escape wheel and ratchet arm. 6 swings!
Removal of the escapement leaving only the pendulum and drop arm gives 60 to 70 swings.
It seems the escapement system is at fault. The wheel revolves very freely but there is quite a shock noticeable as the escapement operates. Some reduction of depth might be advantageous but there is no obvious way of doing this.
Where do I go from here?
I am also puzzled as to the principle of operation of this clock. The pendulum is given an impulse by the fall of the drop arm, which is apparently re-set electrically. But it is not! Fall of the arm completes the circuit causing the armature to be attracted to the horizontal position between the electromagnet arms. There it stays until the circuit is broken. As soon as the circuit is broken the 2 coil springs return the armature and it is this which lifts the arm and re-sets the toggle mechanism. How is the circuit broken? When operated by hand in slow motion the break occurs when the pendulum hits the roller on return swing. This is counter-productive as it takes energy back from the pendulum. Observation of the clock in motion (difficult) seems to indicate that the circuit breaks before the pendulum returns. Perhaps the natural resonance of the arm and contact springs cause a bounce?
Any information?
However, the clock did only 4 or 6 swings between impulses.
Cleaning is suggested as the answer to all ills so this was done: solvent soaking, ultrasonic clean, pegging out holes and polish pivots.
Still only 6 swings!
Motion work removed leaving only the escape wheel and ratchet arm. 6 swings!
Removal of the escapement leaving only the pendulum and drop arm gives 60 to 70 swings.
It seems the escapement system is at fault. The wheel revolves very freely but there is quite a shock noticeable as the escapement operates. Some reduction of depth might be advantageous but there is no obvious way of doing this.
Where do I go from here?
I am also puzzled as to the principle of operation of this clock. The pendulum is given an impulse by the fall of the drop arm, which is apparently re-set electrically. But it is not! Fall of the arm completes the circuit causing the armature to be attracted to the horizontal position between the electromagnet arms. There it stays until the circuit is broken. As soon as the circuit is broken the 2 coil springs return the armature and it is this which lifts the arm and re-sets the toggle mechanism. How is the circuit broken? When operated by hand in slow motion the break occurs when the pendulum hits the roller on return swing. This is counter-productive as it takes energy back from the pendulum. Observation of the clock in motion (difficult) seems to indicate that the circuit breaks before the pendulum returns. Perhaps the natural resonance of the arm and contact springs cause a bounce?
Any information?
