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    New leaf spring prod idea.

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    Zardoz
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    New leaf spring prod idea.

    Post by Zardoz on Fri Dec 21, 2012 3:48 pm

    I have an idea for a leaf spring prod that would compensate for the weak area around the center hole. Have a look at this drawing. Do you think this will work?

    http://i11.servimg.com/u/f11/18/00/01/77/zardoz13.jpg
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    septua
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    Re: New leaf spring prod idea.

    Post by septua on Fri Dec 21, 2012 8:36 pm

    I have seen many crossbows with what are called center shot
    designs. Why can’t a prod with a center hole be adequately reinforced to
    accomplish the same end? Is it due to historical correctness or balance
    considerations?
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    Zardoz
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    Re: New leaf spring prod idea.

    Post by Zardoz on Fri Dec 21, 2012 9:06 pm

    I am planning this for a medieval style cross ow
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    Re: New leaf spring prod idea.

    Post by septua on Sat Dec 22, 2012 1:29 am

    This may be obvious but mounting the prod can done to a
    correct medieval style by creative clamping design giving emphasis to the area
    across the front of the tiller, and not just at the two zones where the bow
    irons pull. Basically I mean using a metal bolster plate that puts adequate
    pressure across the front thus preserving the look that you want. The bow irons
    would apply force to the plate but the thrust will be distributed more evenly
    across than usual. The cord binding method I’ve seen sometimes has a bolster or
    plate like this made from wood.


    Rizzar
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    Re: New leaf spring prod idea.

    Post by Rizzar on Sat Dec 22, 2012 2:12 am

    The "bridle socket" you saw on medieval cord bindings is good to dristribute the binding pressure to the center of the prod.

    You are right, with clamps and plates you can stiffen the center very good, but the clamps must be very tight and stay this tight which is the difficulty.
    Though I think a bolt through the center hole with stiffening plates will do its duty pretty well and you even can hide it unter the bridle socket and cord binding if done properly.

    The center shot is not very historical and due to the forces applied to the center not very practical.

    Zardoz, to your design suggestion:
    Let´s say it simple: every corner in any design is a weakening spot.
    There will be a misbehaviour between the fade out and the working area, the material will need to compensate different forces and in my understanding be a very weak spot.

    Greetings Rizzar
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    Re: New leaf spring prod idea.

    Post by Zardoz on Sat Dec 22, 2012 4:25 am

    I planned on using a binding block, but I didnt mean to put a corner between the fade and the working section. I wrote in the drawing to blend it in. Would a more gradual transition do the trick?

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    Re: New leaf spring prod idea.

    Post by Rizzar on Sat Dec 22, 2012 8:47 am

    As I mentioned before I would stay with the stiffened triangular design.
    It is easy to produce and you most likely won´t run into trouble.

    It
    is a bit hard to describe, but regarding to all the information i
    collected until now a taper that is more "aggresive" than a triangular
    is leaving weak areas.
    So if you go from the center of the prod (the
    area the limb begins concerning the stiffened area) you should have a
    linear taper in cross section.

    (don´t forget the complete center is stiffened, otherwise the triangle begins in the middle of the prod)

    For optimal force distribution a perfect triangle (100% to 0% cross section) would be the best.
    Most medieval bows show values of about 35-40% of the centers cross section at the beginning of the tips.

    Greetings Rizzar
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    Zardoz
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    Re: New leaf spring prod idea.

    Post by Zardoz on Sat Dec 22, 2012 12:30 pm

    I guess it's back to the drawing board. I may just go back to my original plan to use Power Tuff.
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    Re: New leaf spring prod idea.

    Post by mac on Sat Dec 22, 2012 7:54 pm

    Zardoz,

    If you do go back to the drawing board, you might want to reconsider the 2" tiller width that you spec in your drawing. As near as I can tell, most tillers were a lot closer to 1" than to 2". A nice thin tiller goes a long way toward making a bow look good.

    Mac
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    Zardoz
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    Re: New leaf spring prod idea.

    Post by Zardoz on Sat Dec 22, 2012 10:58 pm

    2" was just for illustration. The graph paper was 1/4 inch sqares.

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