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  1. #1
    Join Date
    May 2009
    Location
    Townsville, Nth Qld
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    1,976

    Default Slow pendulum available?

    Thinking of making my first pendulum clock, but don't like the fast moving pendulums with a 2 second period of the swing, too fast, not relaxing to watch. Is it possible to get slower pendulum mechanism, like with a 4 second period?
    regards,

    Dengy

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  3. #2
    Join Date
    Feb 2006
    Location
    Perth
    Posts
    22,958

    Default

    The period of a pendulum depends on the length of pendulum and "g" acceleration due to gravity according to the following approximation.

    length = g x [ (T/2) / Pi ]^2

    Work that out and you will see maybe why T=4 seconds is not popular.

  4. #3
    Join Date
    May 2009
    Location
    Townsville, Nth Qld
    Posts
    1,976

    Default

    So what's wrong with having a 13' pendulum?
    regards,

    Dengy

  5. #4
    Join Date
    Nov 2005
    Location
    Darkest NSW
    Posts
    2,659

    Default

    Absolutely nothing....for those of us with 14' ceilings

    T=2 is about the practical limit, unless the value of g is markedly different at your house? Mind you, I have noticed that gravity does seem to be higher in close proximity to valuable objects....

  6. #5
    Join Date
    Feb 2012
    Location
    nsw
    Posts
    24

    Default

    It is possible to design a compound pendulum. There are a number of spreadsheets on the net which will help with weights and the position. One was on Brian Laws Clock blog a couple of years ago and I think he said they they are not that easy to adjust. Perhaps you need to build in a method of moving the weight a small repeatable amount

  7. #6
    Join Date
    Dec 2011
    Location
    SC, USA
    Posts
    439

    Default

    You could always do a replica of Big Ben...

    The thing about pendulums and adjusting them isn't really a problem with the pendulum itself so much as a problem with the casework itself swaying sympathetic to the pendulum and the clock stops.. And as the clocks get taller - they sway easier unless the base is really really wide, the casework is very heavy and stiff, and thing is very solidly secured to a heavy foundation...

    So for example - nobody wants a brick clock enclosure that is 6' wide at the base with 2' poured footings for their clock with a 13' pendulum...

    This is a very common problem with "regular" Grandfather clocks if the floor resembles "soft"... Aka any carpeting or rugs will allow them to sway and stop... Even padded laminate floors can do it.. And I have seen trouble with these clocks stopping when they were set up out in the middle of a "bouncy" hardwood floor....

    Move them over to the corner on top of a pier and stuff a tightly rolled towel between them and the wall and Viola! The clock keep fantastic time...

  8. #7
    Join Date
    Jan 2008
    Location
    Perth
    Age
    55
    Posts
    106

    Default

    That's interesting truckjohn, I have a similar thing going on with my grandfather clock. If all three weights are about half way through their run down, the leftmost weight starts to swing in and out. Once it swung so much it hit the pendulum bob and stopped the clock!
    Swifty

  9. #8
    Join Date
    Dec 2011
    Location
    SC, USA
    Posts
    439

    Default

    Yep - the casework is swaying allowing the clock to sway... The weights go to into "harmony" with the pendulum and "steal" the energy from the pendulum.... And the clock stops...

    Try out tightly rolling a couple towels and wedging them between the top of the clock and the wall...

  10. #9
    Join Date
    Feb 2013
    Location
    New Zealand
    Posts
    2

    Default Fix it to the wall!

    It's always a good idea to fasten the clock firmly to the wall, for security as well as timekeeping. Specially if you are in Christchurch and get earthquakes. I lost a Grandmother I'd fixed for a friend in February 2011 - the movement was way beyond repair. Yes, I know what I just said, but it was only a test run for timing......

    I've built a few wall clocks, but the only Long Case I've completed was a Bornholm style, because my wife's family comes from there. I designed it from photos we took on the island and fitted a Hermle weight-driven movement. It has survived several thousand noticeable quakes in all, although the house didn't - we're in a new one.

    Current project is a period case in walnut for a 300 year old French long case movement, which I can't design until I have it going properly so I can get the weight drop and case height right.

    David PIMG_0411.jpgrovan

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