RSM runs too fast... Always

Isaac

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Aug 5, 2013
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So, recently got this RSM clock all ticking away after it was sitting on my workbench and waiting for a new SS. The original suspension spring had been broken, so I measured out the broken pieces and got a new SS from Timesavers and hand finished it to fit the movement properly. However, there's quite an issue that I don't know how to fix. The clock gains time extremely fast (~7 minutes over the course of last night - recorded at 1:00 AM to 12:30 PM today). The pendulum bob is set low as the rate nut will allow without falling off, and the pendulum crutch is almost touching the top of the pendulum rod's cutout, so a longer suspension spring would not be able to work. The escapement looks original and seems to function fine. A thought flashed in my mind that maybe this was supposed to be a wall clock movement, but there's no indications of movements being switched out (and the movement looks identical to a large RSM bracket clock I own). The pendulum assembly looks the same as my other RSM clock, so my mind is quite baffled at this.

Any ideas? I've ran out. Some pictures of the movement and the pendulum:

IMG_2371.jpg IMG_2851.jpg IMG_2848.jpg IMG_2849.jpg
 

Willie X

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Feb 9, 2008
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Have you ever seen this clock keep time?

You probably need about 1/8" more length and it looks like you have that in the case.

The rating rod could have been broken off, or you could have a wrong replacement on the bob. Those would be my first two guesses. A smaller bob, or a bob with half moon cutout at the bottom will do it.

Willie X
 
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FredWJensen107

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Have you ever seen this clock keep time?

You probably need about 1/8" more length and it looks like you have that in the case.

The rating rod could have been broken off, or you could have a wrong replacement on the bob. Those would be my first two guesses. A smaller bob, or a bob with half moon cutout at the bottom will do it.

Willie X
 

Isaac

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Have you ever seen this clock keep time?

You probably need about 1/8" more length and it looks like you have that in the case.

The rating rod could have been broken off, or you could have a wrong replacement on the bob. Those would be my first two guesses. A smaller bob, or a bob with half moon cutout at the bottom will do it.

Willie X
Indeed, it is much likely the case that the rating rod snapped somewhere. I took a bob from my other RSM clock and put it on this one - a very nice fit, and the rating rod goes almost to the bottom of the case. How these types of parts get damaged/broken off is beyond me, but I've seen stranger. The rating rod seemed like it was cleanly cut, but I highly doubt a clock would be sold if it gained 40 minutes per week due to a faulty pendulum bob. Perhaps it was an improper replacement.

Some pictures of the new pendulum assembly (long one), versus the one that came with the clock originally (short one). I doubt I'll have any trouble regulating this movement now.

Thanks Willie.

IMG_2853.jpg IMG_2852.jpg
 

FredWJensen107

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Thanks a million for your experience. My pendulum could extend 1/2 more to the bottom. So I will extend my rod, it is a simple brass rod. I will try that first, if that is not enough then I will consider making my pendulum lighter?
 

Isaac

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Thanks a million for your experience. My pendulum could extend 1/2 more to the bottom. So I will extend my rod, it is a simple brass rod. I will try that first, if that is not enough then I will consider making my pendulum lighter?
Pendulum weight has little to no effect on the going rate, the length and size/shape of the bob makes a difference (along with other factors like the clock being in beat, the pendulum period, etc). Extending the rod would be the way to go if you have the necessary skillset.
 

ChimeTime

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My pendulum could extend 1/2 more to the bottom. So I will extend my rod, it is a simple brass rod. I will try that first, if that is not enough then I will consider making my pendulum lighter?
When you hear everyone say "lengthen the pendulum" what we actually mean is lengthen the distance from the point the suspension spring hinges to the bob's center of gravity. In normal situations simply lowering the bob does that. But in your case, with the short pendulum rod, you could also add weights to the bottom of your bob, and/or lighten the top of the bob. Both these options move the center of gravity lower, which will slow the clock.

Where the mass is positioned is much more important than the physical weight of the mass.

So maybe the place to start is by simply taping some lead fishing weights to the bottom of the existing bob !
 
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FredWJensen107

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Mar 24, 2019
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When you hear everyone say "lengthen the pendulum" what we actually mean is lengthen the distance from the point the suspension spring hinges to the bob's center of gravity. In normal satiations simply lowering the bob does that. But in your case, with the short pendulum rod, you could also add weights to the bottom of your bob, and/or lighten the top of the bob. Both these options move the center of gravity lower, which will slow the clock.

Where the mass is positioned is much more important than the physical weight of the mass.

So maybe the place to start is by simply taping some lead fishing weights to the bottom of the existing bob !
 

FredWJensen107

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good idea.
I plan to buy some micro copper tube and splice the pendulum to extend it 1/2 inches. But I will try adding weight under the bob first to see if that works.
Someone asked if I ever saw this clock running..No I never did. I am at least glad that it is running at all. a clock made in 1780 will always be a mystery.
 

kinsler33

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Nice clock. And thanks for explaining why some pendulum bobs have semi-circular cut-out at the bottom.
Some cheap clocks have hollow sheet-steel bobs, and I've had luck pouring a dozen or so #12 lead shotgun shot into the hollow.

Mark Kinsler
 

JTD

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Sep 27, 2005
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Someone asked if I ever saw this clock running..No I never did. I am at least glad that it is running at all. a clock made in 1780 will always be a mystery.
Which clock are talking about? I don't see any clock here made in 1780 or have I missed something?

JTD
 

shutterbug

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No one has mentioned a thinner suspension spring. That would also slow things down.
 
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