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Crutch height and effect on regulation

harold bain

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I've been playing around with a cuckoo clock this weekend (I know, I need to get a life).
The crutch was bent up really high, but I thought I would try running it anyway to see if it would work.
I had to put the pendulum up really high to make it keep time.
Today, I straightened out the crutch, which changed its interaction with the pendulum rod by about 2 inches.
This changed the timekeeping by enough that I had to lower the pendulum bob (leaf) by about 1 1/2 inches.
This may cure a few clocks that have their pendulums scraping the bottom of the case to keep time. Just raise the crutch.
Comments:???:
Harold
 

harold bain

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Nov 4, 2002
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I've been playing around with a cuckoo clock this weekend (I know, I need to get a life).
The crutch was bent up really high, but I thought I would try running it anyway to see if it would work.
I had to put the pendulum up really high to make it keep time.
Today, I straightened out the crutch, which changed its interaction with the pendulum rod by about 2 inches.
This changed the timekeeping by enough that I had to lower the pendulum bob (leaf) by about 1 1/2 inches.
This may cure a few clocks that have their pendulums scraping the bottom of the case to keep time. Just raise the crutch.
Comments:???:
Harold
 

Term

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Jan 2, 2006
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Harold,

For a rookie like me please describe which part the crutch is, this may help me with another clock.

Thanks :)
 

harold bain

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Term, the crutch is the part that is directly connected to the verge (or anchor), that the pendulum rod slips through. Most clocks don't have any way to adjust the point of interaction without major changes.
Harold
 

Scottie-TX

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Well, it's intuitive to think crutch length would affect regulation but in theory I don't believe it should. We don't have theoretical clocks however and I posit whether perhaps it may have more affect on a recoil escapement than on a deadbeat. If the crutch was RADICALLY short, I can see it affecting the escapement in a negative ( not good ) manner. So if your experience could suggest that RADICALLY changing the crutch length for regulation change - I suspect other aspects of EFFICIENT operation may be affected negatively. In short; I couldn't recommend DE-TUNING a clock to achieve some other purpose. I suspect the factory length of crutch was designed for OPTIMUM performance. Just a thought.
 

harold bain

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Scottie, the clock I was working on was a basket case that a fellow club member had given up on. It has a bottom of the case bellows, that I think the previous repairman had trouble getting the crutch around, so he bent it way up. I left it like that to test the rest of my repairs. I set the pendulum to the point that it was reasonably accurate overnite.
Today, I finished repairs, and bent the crutch back to where I thought it should be. I was surprised at how far out the bob was after this adjustment of the crutch.
I have a shelf clock with a pendulum that is close to bottoming out. I think I will try some experimenting with a higher crutch to see what difference it might make.
Harold
 

stewart

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Aug 25, 2004
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Hello Harold

In the June 06 Bulletin see the article on Christian Huygens (pp 300-301), There is information concerning crutch/pendulum geometry. I'm not sure this is what you want but it may be.

Stewart
 

shutterbug

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I postulated this very thing a few months back and was assured that it would make no difference. I accepted the word of those more experienced than I, but still thought they were wrong :) Your experience seems to confirm my feelings. A shorter crutch should cause a faster transfer to the escapement even though the pendulum in theory will still beat the same. Because of that, the amount of impulse should increase which in turn should cause the pendulum to swing a larger arch, slowing the clock. Does that make any sense? I compare it to lowering the fork on a 400 day clock to increase the swing.
 

Bruce Weeks

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Feb 16, 2006
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Could there be an effect due to the gap between the crutch loop and the pendulum rod? Higher up would make the crutch go to a wider angle before impulse occurred. I would think then that would lead to less power, shorter swing, faster rate.

Anyone have an opinion on that?
 

shutterbug

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Bruce - just opposite of what I expect. It will be interesting to see what others think :)
 

harold bain

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Stewart, I reread that article and it does to a small extent explain what I observed. Basically, the higher the crutch, the wider the pendulum swings, which takes longer per swing, causing clock to lose time, which requires pendulum bob to be raised to regulate.
A simple experiment will demonstrate this.
With a simple 20 inch (or any size) pendulum at rest, impulse it by a one inch push at the bottom. You get a one inch swing. Take the same pendulum and impulse it one inch 3 inches from the top. The swing is much wider. The closer to the top, the wider the swing.
Therefore, raising the crutch should help compensate for a pendulum that is scraping the bottom of a clock's case.
Case closed!!
Harold
 

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