A Mechanical Synchronome
This about a weight-driven wooden clock that I built that wasinspired by an electro-mechanical clock, the Synchronome.
It is twelve, fifty-eight and thirty-two seconds.
It is twelve, fifty-eight and thirty-two seconds.
Like the original Synchronome, the pendulum is powered by a gravity arm pushing down on a pallet but the rest of the mechanism is different. 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 might be improved by giving the pendulum rod a coat of yacht varnish or by replacing it with a carbon fibre or invar rod.
The gathering arm (light blue) attached to the pendulum turns the count wheel (red) one pin every 2 seconds (on its swing to the right), one revolution a minute. One pin (white dot) is longer than the rest. 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. |
|
Count wheelThey say that a count wheel drains power from the pendulum and disturbs its regularity. I was kindly given a packet of synthetic-ruby bearings so I decided to replace the miniature ball-bearings in the count wheel. They are very low-friction and the wheel will now spin just by blowing at it. The driving weight was reduced by 20% and the amplitude of the pendulum increased. The count wheel was cut from plywood and drilled for the pins using CNC. The holes for the 5 spokes (2.5mm dowels) were drilled with a Proxxon drill fitted to the tool-post of my lathe. The spokes were inserted before the rim was detached from the hub. Bottom left.The pawl in the photo above has been replaced by a soft brush of carbon fibers, trimmed as shown. It rests gently against the rim of the count wheel. The outside edge of the rim was finished on a lathe so that the wood fibres were all bent anti-clockwise to engage with the brush - a precision low-friction ratchet on a microscopic scale. |
|
|
The original Synchronome clock was invented by George Bennett Bowell in 1895 and developed and distributed by Frank Hope-Jones. Until the 1960s they were used as master clocks 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 pushes 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 push. 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. |
|