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    Changing brace height

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    Frode
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    Post by Frode on Sun Jan 29, 2012 6:56 pm

    Hello all,
    Pardons if this is covered elsewhere, but I haven't found it. I just got an Alchem steel prod and string to match. According to the web page, it wants a 3 1/2" brace, but when we (it took both Missus Frode and me, and we almost didn't get it done Embarassed) got it strung, it promptly settled to about an inch and a half or two (see below).
    Here's my question. Is raising brace height on a crossbow like a long bow, i.e., twist the string a few times and check again? It's not twisted at all, right now. Or do I have a string problem?
    Thanks,
    Frode
    Changing brace height P1010008_7
    Changing brace height P1010007_12
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    Post by Todd the archer on Sun Jan 29, 2012 7:31 pm

    You are correct, remove and twist up (twist in the direction the serving is wound).

    Not unusual for a new string to stretch some untill it settles in.



    Of course this is alot of work unless you have a crossbow press. I have got to make me one, one of these days.



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    Post by Frode on Sun Jan 29, 2012 8:02 pm

    Thanks, Todd! I'm going to need one of those, too.
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    Post by Gnome on Sun Jan 29, 2012 8:02 pm

    Did it actually stretch that much, or was it just too long to begin with? I've noticed quite a bit of variation with strings I've gotten from Alchem, I ordered a prod and two strings and the strings didn't match at all. One was fairly thick and fit pretty well, only requiring a couple of twists to get to the proper brace height. the other was about an inch longer and much thinner, so far I've only used it for a bastard string.
    I'd set up a bastard string and clamps and get a cocking rope, if I was you. You can rough cut a 2x4 to tiller dimensions with notches for the prod and string and you can span and unspan your prod to your heart's content without undue stress on the missus.
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    Post by Frode on Mon Jan 30, 2012 3:29 pm

    Thanks, Gnome!
    That sounds like the way to go. The notched board is easy enough, the clamps I'll have to mull over a bit, unless there are pictures anywhere.
    Frode
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    Post by Sugarbuzz on Mon Jan 30, 2012 5:10 pm

    I seem to recall reading somewhere about limiting the amount of twists you put into a crossbow string, for safeties sake. Maybe I am mistaking bowstrings, but I'd have sworn that putting too many twists into a string increases its chances of weakening? Maybe someone more seasoned here can shed some light on that? I would say that string looks a bit too long, in my opinion. In my experience it would take a large number of twists to bring it to the proper length. I adhere to a policy of remaking a string if I need to twist it more than 6 times. Just an idea/question I'm tossing out there.
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    Post by mac on Mon Jan 30, 2012 5:51 pm

    I think it would be safe enough to put as many twists in the string you want, but you will lose performance. The more the string is twisted the stretchier it becomes.

    If you have to put in more than about 4 or 5 full twists, it would be better to make a new string. If nothing else, though, you will be able to find out how long the string should be.

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    Post by Gnome on Mon Jan 30, 2012 6:51 pm

    I've gotten away without actual clamps for a bastard string for my steel prod from Alchem, I bent some heavy guage steel wire, about 1/8" thick, to this shape:
    Changing brace height DSCN0046

    Changing brace height DSCN0047
    Sorry so blurry, but you get the idea, I hope. It fits sideways over the tip of the prod, then turns and locks into place in the thinest profile of the prod right inside the nock. I have to pinch and prod the real string a bit to fit inside it but it is pretty secure, especially with the hooks for the bastard string oriented to the outside.
    Oh, and about the "bastard stock"- don't forget some kind of foot stirrup for leverage. A well knotted, sturdy piece of rope will work. It may sound like a lot of trouble to spend all that effort building a dummy tiller, but I've found it handy to be able to string my prods while the real tiller is still in progress, to make sure I'm getting the angle of the prod socket just right.
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    Post by mac on Mon Jan 30, 2012 9:01 pm

    Gnome,

    Could you show us a picture of these gismos on the prod? I am having trouble understand how they attach.

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    Post by Frode on Tue Jan 31, 2012 10:32 am

    @Gnome, I think I know, how this works, but like Mac, I would benefit from a photo, if you have one.
    @Everyone/Anyone, How long should a string be? Same formula as a longbow, nock to nock distance minus 3"? Or something else? The string I have now is simply too long.
    Thanks,
    Frode
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    Post by mac on Tue Jan 31, 2012 11:39 am

    Frode,

    I'm not sure that it is possible to make generalizations about the string length. A lot depends on the amount of recurve, and deflex in the prod.

    Perhaps someone who has worked with these prods can make a specific recommendation.

    Failing that, you would always start by measuring what you have there, and make the new string an inch shorter. That will probably get you a usable string. You can then use the information you gained to decide if you need something different. It will be great practice making strings, and you can hang the ones you don't use up on a nail somewhere in the shop in case you need them later as bastards.

    Or, like I implied earlier; keep adding twists to your current string until the brace height looks good, and then measure the resulting string length. That should get you pretty close to the measurement you need for a new string.

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    Post by Gnome on Tue Jan 31, 2012 2:43 pm

    Changing brace height DSCN0048
    Changing brace height DSCN0051
    Hope this helps. In this case my bastard string is a 26" from one of my FG prods, twisted pretty extremely to get enough tension, but as you can see, you don't have to flex the prod too far to get enough slack to slip the real string over the tips. One could put a piece of cloth or leather under the "gizmo" to protect the prod from marring and scratches, since I haven't applied a final finish yet I haven't worried about it. The tension on the bastard string and the profile shape of the prod dictate that the hooks are going to stay put.
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    Post by mac on Tue Jan 31, 2012 5:27 pm

    Thank you, Gnome. It all makes sense now.

    Mac

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