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    Crossbow string question

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    mazawakhan
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    Crossbow string question

    Post by mazawakhan on Wed Jan 27, 2016 10:54 am

    Im about to make a string for my new crossbow. I am going to make it out of hemp twine to keep it somewhat historically accurate. The twine has a 20 lb rating. What is the rule of thumb for making the string as far as strength goes? I think I remember it being 4x the pull weight of the bow. So that is this correct?

    twedzel
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    Re: Crossbow string question

    Post by twedzel on Wed Jan 27, 2016 1:26 pm

    Before you start, don't assume the packaging is correct. Do a few break tests to get the actual strength of some single strands. Hemp twine is usually made of shorter fibers (poorer quality) than what was historically used. This can leave it prone to weak points. So you want to make sure you are on the conservative side for number of strands per draw weight. Standard recurves tend to go 4-5x draw weight and crossbows higher as they are subject to more forces as well as abrasion. A lot of guys are using 28-36 strands of Dacron (which is rated to about 50lbs) on their Excalibur bows. So you can see a large margin of safety is probably a good idea given the forces involved and the potential damage to the bow if it breaks. Also heavy strings on crossbows is less of a detriment to performance than it is on recurves.

    kenh
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    Re: Crossbow string question

    Post by kenh on Wed Jan 27, 2016 2:35 pm

    Hemp twine is not going to work very well.  Too short of fibers, and far too many of your 20# strands to make a safe thickness string for any reasonable poundage bow. 

    Long strand flax (not linen) cord would be much more historically accurate, not very expensive online, and much stronger.

    mazawakhan
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    Re: Crossbow string question

    Post by mazawakhan on Wed Jan 27, 2016 5:31 pm

    kenh wrote:Hemp twine is not going to work very well.  Too short of fibers, and far too many of your 20# strands to make a safe thickness string for any reasonable poundage bow. 

    Long strand flax (not linen) cord would be much more historically accurate, not very expensive online, and much stronger.
    Thanks for the input! Can you point me to a place that sells this stuff?

    kenh
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    Re: Crossbow string question

    Post by kenh on Wed Jan 27, 2016 8:57 pm

    Craft Shops - sewing & needle work type crafts.  Some hobby shops.  Ebay -- search on flax cord or flax string.  Or just google "flax cord" and see how many thousands of places sell it...

    OrienM
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    Re: Crossbow string question

    Post by OrienM on Thu Jan 28, 2016 7:07 am

    I made my string from hemp (cheap cord from walmart)...I'd agree it's weaker than some other natural fibers, but  it can be done if the string is made thick enough. Mine is fully 3/8" thick, with heavily reinforced loops...I quickly broke several lesser strings before I got this one to work.

    So, it can work, but using good quality flax will give you a better chance of success. Given the time it takes to make up a decent string (for me, about four hours...), it makes a lot of sense to use the best materials for the job.

    Xamllew
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    Re: Crossbow string question

    Post by Xamllew on Fri Jan 29, 2016 12:23 am

    Hemp gets pretty fuzzy but it certainly will work for bows under about 200lb draws. I've been using a fairly thick 3/8" flemish twist hemp string served with dacron for several months of regular use, the added thickness might rob a tiny bit of performance but I prefer the natural look of it over dacron.

    mazawakhan
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    Re: Crossbow string question

    Post by mazawakhan on Fri Jan 29, 2016 10:53 am

    Thanks for the replies! I had some B50 laying around and made an initial string yesterday on my homebrewed jig. I will try and make a hemp string this week sometime. My crossbow pulls just under 200.

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