Briggs Rotary

A Wooden Briggs Rotary Clock  

This is my version of the Briggs Rotary Pendulum clock. Patented in 1855 by John C. Briggs it is a clock with a rotary or conical pendulum and has no escapement in the strict sense. Because the motion of the gears is smooth with no interruption as in a traditional escapement the conical pendulum found use as drives for astronomical telescopes and light house beams.

I think its use for a domestic clock can only be decorative or for novelty. The system was employed by other manufacturers such as Henri Farcot who produced higher quality and more decorative clocks.

The clock is 30cm high and 25cm from front to back. As much wood as possible has been used in its construction.

All the gears are laser cut from 3.2mm plywood with ratios to suit the frequency of the rotating pendulum which is a 250g lead fishing weight suspended on thin nylon fishing line. Fine adjustment of the time period is achieved by changing the length of the suspension.

The clock is driven by a spring in a wooden going barrel under the base and is rewound periodically by a small electric motor. The drive enters the gear train 3 wheels down from the 'escape' wheel to reduce the power storage requirements with the disadvantage of more frequent rewinds.

Even power transmission is essential for this type of clock to prevent the weight either climbing out of the fork or decaying and striking the centre mount. After much trial and error of various springs in my possession I achieved suitable power by rewinding every 35seconds for 5 seconds. I would have liked it to be longer between rewinds but was unable to achieve it. With no special effort to adjust the clock it is gaining two minutes a day.

In the video below the white powder around the spring barrel is 50 micron PTFE powder which makes a good dry lubricant. It is a brilliant material for use in wooden clocks for reducing friction.

The drive to the hands is turned through 90 degrees by using a wooden contrate and spur set of gears and this is also can be seen in the video,

One consequence of a 250g weight swing in a wooden structure is that the whole clock, despite bracing, has a perceptible rock and roll. I call it a feature.