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Hills Hoist Mechanism

  1. Jul 3, 2016 #1
    Firstly, am struggling to wrap my head around exactly how the mechanism for a traditional 'hills hoist' (as seen below) clothesline functions.

    Hills_Hoist_Balwyn_Victoria.JPG

    The handle can be turned in order to raise the clotheslines but from my googling, the mechanism is different to what I was expecting.

    Would be greatly appreciated if someone were able to explain to me how systems such as the ones shown below function.

    repair-kit-heritage-hoist.jpg
    $_90.JPG

    Does the entire handle assembly move along the central threaded rod, pushing up the upper section?

    If so is there a way to achieve this with the handle assembly fixed?

    Feel like it's probably quite a simple answer but haven't been able to find much specific information on it
     
    Last edited by a moderator: Apr 19, 2017
  2. jcsd
  3. Jul 3, 2016 #2

    billy_joule

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    Science Advisor

    No. In the top image, the only visibly moving parts are the crank handle rotating and everything above 2/3 the height of the fence moving upward (the photo shows it in it's lowermost position).

    In your second image:
    Only the threaded rod moves up or down,it doesn't rotate, all others parts rotate or are stationary.
    The hand crank rotates the LH bevel gear which rotates the RH bevel gear whose internal threading drives the lead screw up or down. The lower brass coloured collar prevents the lead screw from rotating.
     
  4. Jul 3, 2016 #3
    Thanks for your response.

    So that means the handle assembly is fastened to the exterior stationary pole in some way correct?

    I need to make a system like this where the threaded rods extends but want it to rotate through 360deg (preferably only once) as it extends. is there a way to achieve this by modifying a hills hoist or am I on the wrong track completely?
     
  5. Jul 3, 2016 #4

    jim mcnamara

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    Staff: Mentor

    The reason for lots of turns is: in general mechanical advantage increases as the rate of the extension per turn decreases.

    Questions you need to answer:
    So - how much extension or retraction is required for one revolution?
    Diameter of the central shaft == ?
    Mass of the "stuff" or payload at the top of the rod == ?
     
  6. Jul 4, 2016 #5

    billy_joule

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    Science Advisor

    That's right.

    If you replaced the lead screw with one something like this:
    Helix cut lead screw.PNG

    It'd rotate once per full height extension. Though, that'd be very difficult/expensive to make.
    If you give us details of what you're trying to do we may have better suggestions.
     
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