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    My larp crossbow

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    Istobla
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    My larp crossbow

    Post by Istobla on Thu Dec 15, 2011 8:58 pm



    Bamboo bow, poplar stock, para cord bowstring,(had made a nice one but it broke from running down the bamboo guide) and baltic birch plywood trigger and nut. the triger works just like a rolllock but with a tail i can rest my thumb on when its cocked, so it doesn't accidentally go off.

    the bolts are made from golf tubes with ducktape and foam. they go on the bamboo shaft.
    it draws about 40lb at 10" as measured by a luggage scale.

    its not pretty but i wanted to see what you think. most material choices were made by what i had around and that rona had a great deal on 4"x7 food bamboo poles
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    stoneagebowyer
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    Re: My larp crossbow

    Post by stoneagebowyer on Fri Dec 16, 2011 2:25 am

    Using what you have on hand is very satisfying, isn't it? Nice job.

    You may want to smooth down the edges for the top / table with a cabinet scraper or even a pocket knife or utility knife, and some sanding, so you have longer string life.
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    Geezer
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    Re: My larp crossbow

    Post by Geezer on Fri Dec 16, 2011 7:53 am

    The larp crossbow looks pretty good for an initial essay in the craft. Golf-tube bolts are fairly soft at the butts, so having your bolt rest some distance in front of the lock means the string will strike the bolt at speed, the bolt will flex on impact, and energy will be lost. Try making your bolt long enough so the tail rests just in front of the lock. That way, the bolt's butt won't flex nearly as much (particularly if the 'ring' in the golf-tube is at the rear) You'll get a much more efficient takeoff.
    Also, you've got a lot of string down-pressure on the 'table' that translates into lost energy. If you could angle the prod a bit forward at the top edge, you'll get less lost energy to drag. That, allied with a very smooth top and a bit of lubrication will give you better performance with no greater draw-weight. Keep up the good work. Geezer
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    Basilisk120
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    Re: My larp crossbow

    Post by Basilisk120 on Sun Dec 18, 2011 9:31 am

    Looks good. Don't have much to add to what the other have said.

    Should be effective on the field.



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    Ivo
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    Re: My larp crossbow

    Post by Ivo on Tue Jan 10, 2012 2:47 pm

    Man, I missed this topic!!!

    Haha, think I'll try and make up for it somehow. Laughing

    This bow is actually pretty sweet and definitely deserves some finishing
    touches...ie. smoothing of rough edges, shaving off some unnecessary
    material, and making a nice string...while all these esthetics are to be wished for good looks...there is a detail I noticed in the functional department that can greatly improve the performance of this bow.

    Also, you've got a lot of string down-pressure on the 'table' that
    translates into lost energy. If you could angle the prod a bit forward
    at the top edge, you'll get less lost energy to drag. That, allied with
    a very smooth top and a bit of lubrication will give you better
    performance with no greater draw-weight. Keep up the good work. Geezer

    This is the first time I've see the bolt clip used in such a way...reminds me of a pen clip. Smile

    Problem is...

    The performance robbing friction that Geezer speaks of is actually further enhanced by this feature. I imagine since the clip also serves as the surface for the string to ride one, the downward pressure of the string on the clip is actually *gripping* the bolt and creating even more resistance for the bow to tackle.

    I can see a great improvement in performance once you move the clip above the string and make a groove for the bolt to ride in as pictured below.



    This way the string will only ride on the stock and will not meed any resistance along it's path...also this allows you to nock the bolt properly and reap the benefits of a longer smoother bolt acceleration as Geezer mentioned.

    Hey, Happy LARP'ing.

    Ivo




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