Very Low Q

[duncan webster 1Participant @duncanwebster1]

I was given parts of this clock, including the top suspension, so I finished it off using a magnetic drive using a pendulum impulser coil ex ebay. It works but has 2 issues

1. The Q value is very low, not actually measured but from a semi arc of about 4 degrees, it comes to a dead stand in less than 15 minutes. The only things I can imagine causing this are that the suspension spring (came with the bits) is about 0.008″ thick, which feels to me to be quite thick, and it is hung from one screw positioned behind the suspension bracket, so it could be twisting relative to the wall. There are2 jacking screws at the bottom for setting the verticality against the wall.
2. It appears very sensitive to changing the swing each side of the coil. If it is gaining and I take off and then replace the hood (which can move the whole affair on the wall) it can have unpredictable effects.

Once SWMBO finally agrees a position and I’ve made something like a PicPet to actually time left and right swings I can sort out issue 2, but anyone got any suggestions as to what is causing the low Q? The shiny cylinder to the left of the pendulum is an aluminium cylinder supporting a Hall effect switch, and the copper ring round the coil has a slit in it, so isn’t a shorted turn

[John HaineParticipant @johnhaine32865]

The spring is probably twice or more thicker than it needs to be. I generally use 0.1mm BeCu shim which is plenty strong enough. But the spring shouldn’t absorb much energy. Worth checking the clamping chops to make sure they are flat, I found that changing these gave quite a significant improvement in Q. Most likely as you say is an insufficiently right mounting to the wall. I would aim for two stout screw dowels in the wall either side of the pendulum bracket.

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