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    Proof of concept pulley bow

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    Dauntless
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    Proof of concept pulley bow

    Post by Dauntless on Fri Feb 22, 2013 9:19 am

    This is quite a crude effort by the standards of this forum, but maybe if I post, others won't feel so bad with their work tongue

    I've made a couple dozen bows but have yet to make a serious, working crossbow. The precision work required for them seems to be the challenge.

    It's more of a prototype toy than a serious weapon. The bow draws 4lbs at 12" and shoots bamboo skewers. I wanted to see if a simple roller nut mechanism could be done with crude materials (worked fine with a 25lbs draw) and if I could wrap my little head around how wheelie bows work (still not too sure). I was inspired by this crossbow's mechanism: http://thearbalistguild.forumotion.com/t774-compound-project

    There is no let off on these round cams, but they do allow a much longer draw length for a short prod. The cams are made of apricot wood; slices I took from a branch to make buttons... The roller nut is a section of an oak branch. Trigger pull is very light and there is no safety either







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    Re: Proof of concept pulley bow

    Post by kenh on Fri Feb 22, 2013 4:24 pm

    Looks pretty darn good to me! Even if it is a "wheelie bow" I wouldn't call it crude. It is, after all, a proof of concept. And it sounds as if you proved to yourself that it works.

    Now's the time to scale it up and make something bigger or more powerful. How about a wheelie pistolbow with an 80 lb draw on a 12" prod?

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    Re: Proof of concept pulley bow

    Post by Dauntless on Sat Feb 23, 2013 6:02 am

    Well I have a bamboo backed ipe prod ready for the task. I think I might cut it in half and bolt to the tiller with some deflex to simplify stringing and allow a decent brace height. I also need to make a proper roller nut mechanism with a tighter fit, this one is iffy at best.
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    Re: Proof of concept pulley bow

    Post by kenh on Sat Feb 23, 2013 6:39 am

    Don't know that I would literally 'bolt' the prod to the tiller....

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    Re: Proof of concept pulley bow

    Post by Dauntless on Sat Feb 23, 2013 6:56 am

    Bolt is definitely not the right word, I was thinking of attaching (maybe with B50 or sinew and hide glue) the two limbs to a triangular head that could then be attached to the tiller. The idea is to have a wide v shaped prod that gets pulled together by the pulleys.
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    Re: Proof of concept pulley bow

    Post by kenh on Sat Feb 23, 2013 8:50 am

    Oh right.... I forgot. Had to look at that design again. If your Bamboo/Ipe limbs are covered with fiberglass at the ends (to prevent cracking), then 'bolt' can certainly be the operative word. Although, figuring out some sort of socket would certainly be a bit more elegant.

    I've thought about a pistolbow design where that triangular block (and the action) are sitting on top of one's fist grabbing the pistol grip.

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    Re: Proof of concept pulley bow

    Post by Dauntless on Sat Feb 23, 2013 8:56 am

    Oooh I didn't think of a socket, that might be better for taking the massive strain of the limbs bending.

    Then again cutting and splicing the limbs back together at an angle might be an easier solution.

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