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    Why the ratchet in Greek gastraphetes can hold on the string force?

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    stm2010
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    Why the ratchet in Greek gastraphetes can hold on the string force?

    Post by stm2010 on Mon Jan 29, 2018 8:15 am

    Why the rachet in Greek grastraphetes can hold on the string?
    I am afraid the string force on the sliding plate will cause the rachet leave out the teeth rail.
    Thanks for explanation on my question!

    https://www.youtube.com/watch?v=HTZ5a9FouVg




    F is the string force acting on the sliding plate.
    Will the f2 force pull out the claw from the  ratchet tooth  ?
    Dark Factor
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    Re: Why the ratchet in Greek gastraphetes can hold on the string force?

    Post by Dark Factor on Sun Feb 04, 2018 11:52 am

    Because the rail has a V cross section  (dovetail). You can only slide the trigger from the tip of the gastraphete.

    I'm making a gastraphete, so maybe in some months I could show you some pictures... if the corn bow works!

    The machine on the video isn't a gastraphete (the portable version), but I think that's also a dovetail rail.
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    Re: Why the ratchet in Greek gastraphetes can hold on the string force?

    Post by stm2010 on Wed Feb 07, 2018 8:00 am

    Dark Factor,Thanks,I figure out this problem through some blue print of gastraphetes.

    The main function of ratchet is prevent the horizontal movements of the sliding plate.
    If well design the pawl shape, it also can aviod the  vertical movements of the sliding plate.
    Dark Factor
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    Re: Why the ratchet in Greek gastraphetes can hold on the string force?

    Post by Dark Factor on Wed Feb 07, 2018 12:20 pm

    Yes, it depends of the shape of the ratchet and its length (longer ratchet, less vertical force).
    But in the ancient text of Heron of Alexandria, he speak about a dovetail (which works perfectly).

    For biggest machines, I don't know exactely if there is a dovetail, but if there is a rope to bend the bow, there are less risk.

    here the french translation of the old greek text (sorry I speak better french than english) : http://remacle.org/bloodwolf/erudits/heronalexandrie/chirobaliste.htm

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