American Replacement banjo movement time issue

Discussion in 'General Clock Discussions' started by timecollector, Aug 1, 2019.

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  1. timecollector

    timecollector Registered User
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    Jun 24, 2009
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    Retired law enforcement
    Beverly Hills, Florida
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    I have been in the process of restoring what I believe to be a Horace Tifft banjo clock. All I had was a damaged case so I had to buy a movement, weight and pendulum. the movement is a fairly early banjo movement. I purchased a 7 lb weight. The clock runs slow no matter how far up I put the bob. I tried a 6 lb weight but it got slower.

    Any thoughts as to the correct weight or other reasons the clock runs slow. If I shorten the pendulum it would be up in the throat of the clock. I do at least one restoration a year. This case was just such an interesting case I wanted to try to bring it back as best as possible.
     
  2. bruce linde

    bruce linde Technical Admin
    NAWCC Member

    Nov 13, 2011
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    oakland, ca.
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    the length of the pendulum is going to determine the rate... the weight just powers the movement.

    it would help to see photos of everything, including suspension spring and bob... but the way to know for sure how long the movement wants the pendulum to be is to count the teeth of the movement gears and do the math.

    i had a similar issue with a banjo clock and solved it by making a bob that was full-sized brass in front (for viewing through the lower tablet glass) but only had lead in the top half behind the brass... this moved the center of mass in the bob and assy up and the clock now keeps good time.
     
  3. Willie X

    Willie X Registered User

    Feb 9, 2008
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    Wrong movement ... probably for a shorter case. You don't have many choices. The 'trick' pendulum already mentioned, or replacing the movement's escape wheel with one having fewer teeth. How many less teeth is always a tuff question! WIllie X
     
  4. Uhralt

    Uhralt Registered User
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    Sep 4, 2008
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    It is not that tough if you can run the clock in its current condition. Take a pendulum with a length that fits the case and let the clock run for a defined time. Note the difference between the correct time and the time the clock shows.
    An example: The clock has run for 10 hours. Starting time was 8:00 AM. After 10 hours, the clock shows 4:00 PM. Correct time would be 6:00 PM. Therefore, the clock has run for 600 minutes but it shows only 480 minutes. Therefore the clock is 20% late. To correct this, you need an escape wheel that has 20% less teeth than the one you currently have. If your current escape wheel has 40 teeth, the correct one should have 32 teeth.

    This is, of course, a simplified example but if you run the test and insert the real numbers you find, you should be able to find a fitting escape wheel.

    Uhralt
     
  5. Willie X

    Willie X Registered User

    Feb 9, 2008
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    Yes, I agree, the percentage method is simple and works well if the difference between what you have and what you need isn't too much. Willie X
     

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