Runs a tiny bit fast... bob is as low on the pendulum as possible.

Discussion in 'General Clock Discussions' started by trschaefer, Jan 11, 2018.

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  1. trschaefer

    trschaefer Registered User
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    I just got this weight driven banjo clock on eBay. Seller warned me that it ran a little bit fast. So I've got the bob as low as possible on the pendulum that came with the clock. He was right... It gains about 5 minutes after about 4 or 5 days. I know there is some mathematical formula (which I'd rather avoid...) for determining the correct pendulum length for a specific clock movement. I was just wondering if there was anything else I could try "short" of getting a "longer" pendulum rod... The clock case could accommodate a slightly longer pendulum rod. Does the weight of the bob have any impact? Probably not... The clock has not stopped running since I hung it up a about a month ago. So everything else seems fine. Thanks.

    IMG_20180111_191337699[1].jpg
     
  2. bruce linde

    bruce linde Technical Admin
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    assuming all original, the bob would ideally be centered in the viewing window of the bottom tablet... and it looks kind of low to me, as is.

    have you had the hands and dial off to see what's under the hood? maybe some of the original pics from when you bought it?
     
  3. THTanner

    THTanner Registered User
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    a clock that is out of beat will sometimes run too fast as the pendulum short cycles. Try setting the beat really well and see if your clock is affected this way.
     
  4. leeinv66

    leeinv66 Super Moderator
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    Longer suspension rod will be the likely cure. You could try a thinner suspension spring, but that is probably the same amount of work as making a longer rod.
     
  5. Willie X

    Willie X Registered User

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    Placing a thin strip of lead (about
    1/4 ounce) at the top - back of the pendulum bob will do it. You can secure it with a dab of E-6000 or double sided tape.

    Many of these have a keystone type suspension assembly. It's common for the old suspension spring to have been broken off and repaired. So, your cure could be as simple as restoring the suspension spring to its proper length.

    IMOE, the clock makers back then weren't so particular about the position of the pendulum. Lower was more prevalent than higher and only a few were exactly where you would think they should go.

    Willie X
     
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  6. THTanner

    THTanner Registered User
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    Since it is running too fast, would you not want the added lead at the bottom - back of the bob ?
     
  7. shutterbug

    shutterbug Super Moderator
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    I'm with the opinion that the spring probably broke and was put back on. A new suspension rod and spring is the likely best solution. All of the usual suppliers have them.
     
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  8. Willie X

    Willie X Registered User

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    Correct-amoondo, lead strip near the bottom. Listen to THT.
    Willie
     
  9. leeinv66

    leeinv66 Super Moderator
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    Not sure that will such a slow it down considering the size of the bob and hence the size of the lead strip you could hide on the back of it.
     
  10. THTanner

    THTanner Registered User
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    I don't usually comment on Willie's posts, but when I do I send him Dos Equis ;)
     
  11. trschaefer

    trschaefer Registered User
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    Great. Now I've got a few ideas of where to go with this problem. Thanks.
     
  12. novicetimekeeper

    novicetimekeeper Registered User
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    You seem to have some diametrically opposed ideas on offer.

    If you want to change the rate by adding a small mass to the back of the bob, adding it at the bottom will slow it down, adding at the top will speed it up.

    Great Clock facts
     
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  13. harold bain

    harold bain Registered User
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    Hope he has room for horses.....
     
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  14. shutterbug

    shutterbug Super Moderator
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    Not always. To speed the clock up, you need to add weight above the center of oscillation. With many suspension-wire-and-bob clocks, the top of the pendulum might get it done. With the more complicated lyre pendulums, above the bob will still slow it down, but not as much.
     
  15. novicetimekeeper

    novicetimekeeper Registered User
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    looks a pretty conventional pendulum setup to me.
     
  16. THTanner

    THTanner Registered User
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    This is true for Lyre pendulums - and perhaps some others. I am currently experimenting with a lyre pendulum for a "94 cm" Urgos movement. While the lyre assembly is about 34 inches long, the center of gravity according to a balance method is about 3 inches above the bob. So adding weight to the top of the bob will slow it down some. Adding weight to the bottom of the bob will slow it down more using the same amount of weight. On those Lyre pendulums it is amazing how much top weight is in those decorative rods, some of which are steel on this Lyre.
     
  17. Bill Ward

    Bill Ward Registered User
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    Very nice clock! If 'twer mine, I'd clean it first- insufficient amplitude makes a clock run faster due to circular error. Next, I'd look at the escapement carefully while running- could it be skipping any teeth? Are all the teeth straight & of even length? Is the beat even throughout the rotation of the escape wheel? Then I'd look at the suspension spring- they are commonly damaged by clueless owners or movers. (Yesterday, a friend told me of a house guest who, unable to sleep because of a heavy marble clock's quarterly chiming, and unsure how to stop it, moved it in the middle of the night into the basement!) Of course, it's always possible that a dealer put on another clock's pendulum.
     
  18. James McDermaid

    James McDermaid Registered User
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    According to the rules a longer suspension rod will slow it down and shorter will speed it up.

    The weight of the bob is not super critical but if the bob is too heavy it may have insufficient swing which will tend to speed it up.

    The engagement of the verge and the escape wheel could have been changed causing it to not get a proper impulse.

    If it has a suspension spring, the spring contributes to removing the circular error and if it has been cut off it looses some effect.

    I have had Welch club foot escapement clocks that I have lengthened the pendulum rod to slow it down and I hit a point it runs faster. These have trapeze type suspension with no flat spring. There is a sweet spot where they will regulate. The crutch needs to fit the suspension rod without being too tight or sloppy.

    Jim
     

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