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  1. #1
    Join Date
    Mar 2013
    Location
    Edinburgh
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    4

    Default Bearing/fulcrum o use for a pendulum

    I want to swing a locket on a chain like a pendulum and I want to minmise the friction experienced where the chain attaches to the supporting post. What sort of bearing or similar device should I use for this? Ideally it should be available in a bronze/dirty brass colour but I guess I can deal with it if it isn't.

  2. #2
    Join Date
    Feb 2015
    Location
    Oz
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    67
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    815

    Default

    Knife edge.

  3. #3
    Join Date
    Aug 2011
    Location
    Melbourne
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    3,775

    Default

    What he said.

    Many years ago in a previous life I work on a gas densitometer. It consisted of a sealed vessel with a float inside. The float was connected to a pendulum with a needle against a graduated scale with the zero position in the middle. It worked by connecting the vessel to a vacuum pump and evacuating the air to close to zero absolute and then introducing the gas to be measured. You would then manually swing the pendulum while introducing the gas and when the "average" position of the needle was zero (time in the +ve equalled the time in the -ve) then you would make calculations and determine the density of the gas from known variables such as the pressure etc..

    My project involved automating that machine by using a sensor to measure the time the needle spent above and below the zero position and then return a digital reading. Anyway, needless to say that this pendulum needed to has the least amount of friction as possible, not that friction introduced any errors as it was equal in both the -ve and +ve regions but the less friction the better. Its design concorporated a lovely knife edge for this reason.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  4. #4
    Join Date
    Mar 2013
    Location
    Edinburgh
    Posts
    4

    Default

    Thanks. Is that something I can buy? I can't find anything on eBay. I also forgot to include the word 'cheap' in my first post!

  5. #5
    Join Date
    Aug 2011
    Location
    Melbourne
    Posts
    3,775

    Default

    Hi,

    Not sure. My first thought was that you would make it. It couldn't be too difficult.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  6. #6
    Join Date
    Jan 2004
    Location
    Mackay North Qld
    Posts
    4,414

    Default

    THX1138

    Welcome to the Metalwork Forum.

    Since we have a jewelry sub forum I'll move this thread

  7. #7
    Join Date
    Feb 2015
    Location
    Oz
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    67
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    815

    Default

    Doesn't get much cheaper than a file.
    Attached Images Attached Images

  8. #8
    Join Date
    Dec 2005
    Location
    South Australia
    Posts
    667

    Default

    I may be missing something here, just use a bail or jump ring

  9. #9
    Join Date
    Oct 2015
    Location
    melbourne
    Posts
    189

    Default

    Just to confirm :
    The pendulum consists of a locket and chain. You want a suspension of that is low cost, but presumably low friction to get maximum 'run time'. Do you need to constrain the direction, ie keep it in a straight line?
    I'd reckon a knife edge as above would be best, but next a suspension spring may be easier. Lots for sale, they are used in clocks.
    Or make one from a short strip of springy brass, for example. Or even 2 parallel threads.
    I think a single jump ring wouldn't control it but is definitely the easiest.




    -russ

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