A Mechanical Synchronome

This about a weight-driven wooden clock that I built that was
inspired by an electro-mechanical clock, the Synchronome. photo of clock It is twelve, fifty-eight and thirty-two seconds.

As with the original Synchronome, the pendulum is impulsed by a gravity arm impinging on a pallet but the rest of the mechanism is entirely different and my version is driven by a weight whereas the Synchronome was powered by an electro-magnet.

Time keeping: My clock has an unvarnished wooden pendulum with a lead bob (weight 5.3 kg) swinging in an arc of 3° with a Q value of about 25,000. It keeps time to about one second from day to day but drifts with changes in humidity, temperature and atmospheric pressure. It is the most accurate clock I have made so far but could be improved by giving the pendulum rod a coat of yacht varnish or by replacing it with a carbon fibre or invar rod.

Once a minute the pendulum triggers the weight-driven mechanism that responds by giving it a push to keep it swinging.

The gathering arm (light blue) attached to the pendulum turns the count wheel (red) one pin a second, one revolution a minute.

One pin (white) is longer than the others. Once a minute, it touches the trigger (green) releasing the gravity arm (purple).

The gravity arm roller drops gently onto the pallet of the pendulum (orange) and falls off the pallet as it moves to the right, giving the pendulum an impulse.

The gravity arm (purple) then lands on the arm of the reset lever (yellow) releasing a hook from a pin on the hour wheel (red).

The hour wheel, driven by a weight on the cord, (brown) turns 1 step clockwise. As it turns it raises the reset lever (yellow) which lifts the gravity arm (purple).

The gravity arm is caught again by the trigger (green) and held just clear of the pallet, ready to give the next impulse.

drawing of a clock

The electro-mechanical Synchronome clock that was my inspiration

The original Synchronome clock was invented by George Bennett Bowell in 1895 and, until the 1960s, was used as a master clock in large institutions and factories which required a precise timekeeper to control all the clocks on the premises.

Once every 30 seconds the mechanism of the master clock releases a lever which impulses the pendulum and sends an electrical pulse to move the hands of all the slave clocks. It also resets the lever ready to give the next impulse to the master clock.

The Synchronome clock also served as the slave clock for the famous Shortt-Synchronome clocks which were the world's best timekeepers in the 1920s and 30s, installed in many observatories.

These were the first clocks that were more precise than the rotations of the Earth itself. Since the 1940s they have been replaced by atomic clocks.

In the meantime, a Shortt-Synchronome under test has been found to have an error of one second in 12 years.

drawing of a Synchronome clock

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