The second replacement spring was fitted on 26 April and the pendulum now appears to be swinging regularly. There was a minor problem with the battery backup that is supposed to tide the auto-winders over power cuts, but that is now resolved. The clock is keeping reasonably good time as the new spring beds in, but the process of regulation will continue for a few weeks. Fingers remain crossed.
The erratic swing of the pendulum was diagnosed as a crooked suspension block, and the reason the suspension block was crooked was that the new spring, being slightly thicker than the old one, was too tight a fit and locked solid before it was fully home, preventing the weight of the pendulum from pulling it square. In the process of trying to square it, the new spring snapped this afternoon. At less than eight weeks in service, most of it stationary, it might be regarded as the Liz Truss of suspension springs.
The new replacement spring will be made next week and fitted the week after. Now that the cause is understood, I am confident that we should have our clock back in a couple of weeks.
It will be obvious that I wrote too soon. The pendulum developed a twist while I was away, and was stopped by Jason Morgan who was kindly looking after it in my absence. The reason for the twist is uncertain, but Cumbria Clocks’ engineer is coming to fix it soon. I’ll update this news item when I learn the whys and wherefores, and hope to have everything running as it should be before long.
I am very pleased to be able to report that after a gruelling day’s work yesterday, the parish clock is back in action and, remarkably, keeping good time almost from the off. (There have been some unrelated issues with the chiming, but these should be resolved soon.)
Below you can see a photo of the broken suspension spring which was the source of the trouble. The top part is sandwiched in a block of brass held secure in the clock frame, while the bottom part is bolted to the top of the pendulum rod. As the pendulum swings in its one second beat, the spring flexes. This arrangement, which is common to nearly all pendulum clocks, avoids any friction in the pendulum but puts high demands on the steel of the spring, which gradually work-hardens with the continual flexing. Amazingly it turns out that the broken spring still had some of the original paint on it, suggesting that it dates from 1897 when the clock was new. This means that it is 126 years old and has flexed around 66 million times. Let’s hope the new one can do as well.
It may interest you to know that the escapement in our clock is the same double three-legged gravity escapement designed initially for the Big Ben clock, and that the recent restoration of that clock was undertaken by Cumbria Clocks who also maintain ours.