An 1848 Scottish clock – relearning sympathetic vibration

In 2020 my wife and I bought a Scottish tall case clock at a live auction. We had wanted one for years and it ticked all the right boxes for us, tall, stately, attractive, easy to repair movement, intact with very little actually missing.

Not one person in the auction hall was interested in the clock and we managed to snag it for $270 plus fees and taxes. It is a shame that it went for such a low price but tall-case clocks are not in particularly great demand right now and with space limitations where would you put one in smaller homes today?

It may not show from the below photo that we took that day in the auction hall but it had been neglected for a long time and needed a lot of work.

At the auction house

The work included repairing the movement and refinishing a very tired case. However, it was a great learning experience and a true labour of love.

After the movement was repaired the testing went on for weeks which included small adjustments and waiting for a new suspension spring and pendulum rod and a stake.

During testing, I encountered a consistent problem. On day six of the weekly cycle, the clock would stop. As the weights descended to the level of the pendulum a harmonic phenomenon occurred that is defined as “a formerly passive string or vibratory body responding to external vibrations to which it has a harmonic likeness”.

English bell strike movement

When the weights on a tall clock descend to the point where it’s at about the same height as the pendulum, the weights swing slightly. Since the power that drives the pendulum is now swinging the weights as well, the pendulum does not get its share of power and eventually stops.

I eliminated the sympathetic vibration by anchoring the clock stand to a wall.

Just after the movement was repaired and in its case, the pendulum had just enough over-swing to compensate for the moving weights and the clock would soldier on. But after two years and a little bit of wear, the clock stops at the point where the pendulum is at the same level as the weights.

Sympathetic vibration can often be addressed in a tall case clock by fastening the upper part of the case to the wall, or by mounting the case on a solid foundation avoiding anything soft such as a carpet. But other measures can be taken if the problem persists.

Scottish tall case clock
Scottish tall case clock

The solution

I had attached an anti-tipping wire between the wall and the clock case which I thought would take care of sympathetic vibration. For a while, that worked but eventually, it would stop.

The solution came in the form of protective packaging retrieved from an Amazon delivery, a dense black foam block placed behind either side of the clock case and at the same height as the pendulum.

Sponge block illuminated with a flashlight

I had forgotten what I had learned during the testing of the movement two years ago and was reminded recently when I read a thread about sympathetic vibration on a clock forum site.

Everything is now put right and this beautiful tall-case clock assembled by William McLachlan from Newton Stewart, Scotland now runs its full cycle without that annoying stop at the six-day point.


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