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    Fraying string?

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    phuphuphnik
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    Fraying string?

    Post by phuphuphnik on Sat Apr 05, 2014 8:22 am

    I'm worried that I might be putting too much stress on my string. It is a 120# Alchem prod with their string. I'm shooting 20-25g (308-385 grain) bolts. I don't know what looks normal, so I'm asking for a sanity check. There is only one or two strands out, and on one side. It looks OK for now as long as not many more fray out, but like I said sanity check. 
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    Hotspur
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    Re: Fraying string?

    Post by Hotspur on Sat Apr 05, 2014 8:44 pm

    I would err on the side of caution and replace the string.  

    As to what's causing it;  make sure nothing is abrading the string in your handling, waxing etc.

    Also, 20 g is a little light (?).  My wild conjecture is that the light bolts may be stressing the string.  

    I would be interested to hear more opinion on that.

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    Re: Fraying string?

    Post by Hermit on Sun Apr 06, 2014 7:29 am

    From the photo,it appears that one possibility is that the string was damaged at some point,also,there seems to be little or no wax on it.I would be inclined to replace the string,and keep it under observation,if the string does not contact of foul the bow anywhere,and it happens with a new string,you have a problem.
                                        Hermit.
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    Gnome
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    Re: Fraying string?

    Post by Gnome on Sun Apr 06, 2014 8:37 am

    I concur with Hotspur and Hermit, I suspect a cut or abrasion on the string. If you continue using it, do wax it well and keep an eye on your brace height. I think if it fails it's more likely to start slipping and getting longer and lopsided than snap catostophically, but keep those safety glasses on just in case!

    I have a crossbow with what I believe is the equivalent prod from Slowbows the SB103 rated at 120 to 140#. I thought your bolt weight sounded a bit light but I just weighed one of my field bolts for that one and what do you know, 23 grams! Those are lighter than I normally go for, I thought I was buying 3/8" oak dowels at the hardware store but they were poplar and I just went with it. They shoot fine though, time after time, so I don't think that's a problem, either.

    Have you considered making your own strings? It sounded intimidating and tedious to me at first, but I must say it's become one of the most satisfying elements of the build process for me.

    Gnome
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    Re: Fraying string?

    Post by Lightly on Sun Apr 06, 2014 10:09 am

    Replace, replace, replace. Each broken strand increase the stress on the other strands, and it will go quickly. I agree with Gnome, too, I was intimidated by string making, but, it is relatively easy, and relieves the stress of having to think about buying another one.

    Lightly

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    Re: Fraying string?

    Post by phuphuphnik on Sun Apr 06, 2014 10:15 am

    I've made strings, I happened to have one for the prod. I actually love making them!  I'll be using a page from Iolo's book and using the artificial sinew> I have that on hand. My stonebow prototype for the 7th grade has one. I love the look of it.  I'll be getting some dacron for my longbow soon enough and move to that. Hemp is a bit of a pain to work with IMHO, quite stiff and comes unraveled from the spool when I'm trying to use it. Plus I don't really trust the craft stuff for some reason. I'm trying to talk my wife into spinning some for me. No luck yet and she'll have my manhood if I use her handspun linen...

    I'm not familiar with failure modes of crossbow strings, hence my asking. I was mostly concerned if it was being broken by the firing or something else.  I'll be adding some weight to the bolts too.
    cheers,
    chriso
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    Re: Fraying string?

    Post by mac on Sun Apr 06, 2014 2:20 pm

    Chriso,

    I recommend against using "artificial sinew".  Nylon is too stretchy to make a good string. 

    If you are comfortable using a synthetic material, then dacron is your best bet. 

    http://www.3riversarchery.com/brownell+b-50+dacron+waxed+bow+string+material_i4144X_baseitem.html

    Mac

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    Re: Fraying string?

    Post by phuphuphnik on Sun Apr 06, 2014 3:31 pm

    Mac,
    Upon reading more I came to the same conclusion. I just ordered some dacron 50 and whatnot. Should have it Friday.

    Which reminds me, I'll be chatting with you soon for more pewter bobs. The students loved the crossbow pins!
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    Re: Fraying string?

    Post by Geezer on Sun Apr 06, 2014 4:50 pm

    geezer here:  weighing in on your frayed-string problem.  I say replace it... you appear to have an entire strand broken... It will go sooner or later, with emphasis on the sooner. 
    As for materials: In the olde-dayes, I made strings of artificial sinew, and while it WILL work, Art sinew is mostly nylon and is way too stretchy to make a reliable string.  You'll end up taking it off the prod and twisting it a turn or two every few days... and eventually it will break.  Do yourself a favor, buy some Dacron B-50 waxed bowstring. I get the tan stuff from 3 Rivers Archery and it works out fine.  For a 150 lb. bow, I use about 50 strands (25 loops on the jig) But you could probably get away with 30 if you want faster flight.  For my lightweight aluminum-alloy bows (@70 lb) I use 30 strands (15 loops) and that works out fine.  Don't let the job scare you.... I swear I could train monkeys to make strings... even my Journey-person Lightly can do it!
    Geezer.
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    Re: Fraying string?

    Post by Lightly on Sun Apr 06, 2014 4:55 pm

    Hey!

    phuphuphnik
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    Re: Fraying string?

    Post by phuphuphnik on Sun Apr 06, 2014 6:47 pm

    Lol,
    I'll use von Eichsfeld's videos. As I said above, I ordered the string. I'll check the archives for a way recipe. I have Viper spit, or whatever it is called. It is OK, but that !@$% tin cost $12. I'm making my own from now on.
    cheers,
    chriso

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