Pendulum question

[phd]

This is hopefully a simple question! I'm more of a watch person than a clock person...so please excuse my lack of the proper terminology.

I have a very basic pendulum clock (an old school clock) with what I believe is called a deadbeat escapement.

The pendulum is suspended by a flexible steel strip which is fixed at the top (of course!) but not directly connected to the pallet. The pallet is attached to a second arm - this time a rigid brass arm. This arm has a slot in it, through which the flexible suspension strip passes.

So, as the pendulum swings on the flexible strip, it naturally carries with it the rigid brass arm which is connected to the pallet.

Does this make sense so far?

Now, the slot in the rigid arm is not a tight fit for the flexible strip - the slot is maybe a millimetre wide, and the strip is much less. This means that, as the pendulum changes direction, there is a small "lag" before it carries the rigid arm with it.

This arrangement makes a little noise of its own, every time the strip moves from one side of the slot to the other. I figured that, if it's making a noise, it's wasting energy.

If I pack the slot with a sliver of card, so that the flexible strip and the rigid arm are now locked together tightly, the swing of the pendulum is greater, and the action just "sounds" healthier.

So, my question (see, we got there in the end!) is this. Why does the slot have play in it, and is it a good or a bad thing to reduce this play as I've tried with my sliver of card?

Phew!
Thanks,
Paul

[John MS]

This is hopefully a simple question! I'm more of a watch person than a clock person...so please excuse my lack of the proper terminology.

I have a very basic pendulum clock (an old school clock) with what I believe is called a deadbeat escapement.

The pendulum is suspended by a flexible steel strip which is fixed at the top (of course!) but not directly connected to the pallet. The pallet is attached to a second arm - this time a rigid brass arm. This arm has a slot in it, through which the flexible suspension strip passes.

So, as the pendulum swings on the flexible strip, it naturally carries with it the rigid brass arm which is connected to the pallet.

Does this make sense so far?

Now, the slot in the rigid arm is not a tight fit for the flexible strip - the slot is maybe a millimetre wide, and the strip is much less. This means that, as the pendulum changes direction, there is a small "lag" before it carries the rigid arm with it.

This arrangement makes a little noise of its own, every time the strip moves from one side of the slot to the other. I figured that, if it's making a noise, it's wasting energy.

If I pack the slot with a sliver of card, so that the flexible strip and the rigid arm are now locked together tightly, the swing of the pendulum is greater, and the action just "sounds" healthier.

So, my question (see, we got there in the end!) is this. Why does the slot have play in it, and is it a good or a bad thing to reduce this play as I've tried with my sliver of card?

Phew!
Thanks,
Paul

Sounds like to have an interesting clock - which maker and model is it. Good research on your part and please post any pictures you have. I'll bet the movement looks something like this. The flattened steel spring with a hook on one end for the pendulum is called a suspension spring. The bent brass wire that attaches to the pallets has a small loop at one end to provide a sliding mechanical connection to the pendulum. That's callled a crutch. A small amount of freedom is needed in that crutch loop to assure the suspension spring and pendulum move freely and receive each impulse from the escape wheel. As long as your clock is running accurately and the tick/tock is equally spaced then I would not bother trying to close down that small space.

If the ticks and tocks are not evenly spaced that can be adjusted by bending the brass crutch ever so slightly to center the action of pallets, escape wheel and pendulum.

[phd]

Hi John,

Thanks for the reply! My movement is a lot simpler (no chime, for starters). I don't think there was a maker's stamp on it - just the place where it was made (I'll check). I would photograph it, but now it's back in the case.

I closed up the slot in the crutch (thanks for the terminology, by the way), but not too tight. I also de-greased the slot and suspension spring, because I think part of the problem was the "sticking" as the suspension spring moved from one side of the slot to the other - this mops up energy. Also, I think the mainspring is probably past its best.

I also set the beat, and polished up a couple of the escape wheel teeth which had "burrs" on them. Now, it seems to be running very nicely, and I've got it regulated to about 30s per day.

I've just bid on a fusee wall clock on eBay, which will be interesting!

Although I mainly work with watches, clocks have their charms too. What I like about them is that they are on the borderline between "blacksmithing" and "precision engineering", if you see what I mean.

Cheers,
Paul

[John MS]

Hi John,

Thanks for the reply! My movement is a lot simpler (no chime, for starters). I don't think there was a maker's stamp on it - just the place where it was made (I'll check). I would photograph it, but now it's back in the case.

I closed up the slot in the crutch (thanks for the terminology, by the way), but not too tight. I also de-greased the slot and suspension spring, because I think part of the problem was the "sticking" as the suspension spring moved from one side of the slot to the other - this mops up energy. Also, I think the mainspring is probably past its best.

I also set the beat, and polished up a couple of the escape wheel teeth which had "burrs" on them. Now, it seems to be running very nicely, and I've got it regulated to about 30s per day.

I've just bid on a fusee wall clock on eBay, which will be interesting!

Although I mainly work with watches, clocks have their charms too. What I like about them is that they are on the borderline between "blacksmithing" and "precision engineering", if you see what I mean.

Cheers,
Paul

Good deal. I'll be interested to hear about that old fusee clock. My interest is in older american clocks. One that I enjoy is the Gilbert Admiral school house style clock below. It has a time only movement with a simple calendar.

Just a bit of clock oil where the crutch slides on the suspension spring will help things. When you oil the movement be sure to put just a bit of oil where the pivits exit the plates. The only gear that should see any oil is the escape wheel, and just a bit on the pallets will suffice. A bit of motor oil on the mainspring coils will allow them to slide until you can disassemble and clean that movement. Recheck the gap that was closed on the crutch and be sure the sides are still parallel.

[phd]

Good deal. I'll be interested to hear about that old fusee clock. My interest is in older american clocks. One that I enjoy is the Gilbert Admiral school house style clock below. It has a time only movement with a simple calendar.

Just a bit of clock oil where the crutch slides on the suspension spring will help things. When you oil the movement be sure to put just a bit of oil where the pivits exit the plates. The only gear that should see any oil is the escape wheel, and just a bit on the pallets will suffice. A bit of motor oil on the mainspring coils will allow them to slide until you can disassemble and clean that movement. Recheck the gap that was closed on the crutch and be sure the sides are still parallel.

Hi John,

I like the schoolhouse clock! Yes, I used a good Moebius clock oil on all the pivots, and just a hint on the escape wheel teeth (wthout the oil, you could hear the pallets sliding on the teeth, which I figured was a bad sign). It seems to be running pretty smoothly now, touch wood!

Paul

[John MS]

Post a picture of your schoolhouse clock when you get a chance.