Primitive Archer
Main Discussion Area => Bows => Topic started by: gfugal on August 13, 2017, 08:48:01 pm
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I'm trying to figure out the best way to make my bowstrings. I have done flemish twist for sometime now, but i heard that the twist in the string allows it to stretch more than it would in say an endless loop. On the other hand, endless loop requires you to get the length perfect while making it, without adjustment after the fact. The strands may also be more likely to snag and get cut if it isn't waxed thoroughly and twisted slightly. It also may lead to weaker loops then the main body (suposedly, may not be true). If that is true than having double thickness in the main string length compared to the loop would cause extra unecessary weight, decreasing performance. Either way there's a disadvantage. I'm not sure which is worse extra weight or a little extra stretch.
A possible solution would be a braided line. That would reduce the stretch from twist while also allowing you to splice loops and bind the loose strings, kreping them together and preventing them from snaging. Has anyone done this? What's the disadvantage to such a string?
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What string material are you using? Do you pre-stretch your strings? I have a jig that stretches them tighter than when on a bow.
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I'm not sure that braided would stretch less than twisting. I would think it may be tougher to get even strain on the individual strands with a braided string.
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Skip to the 16:00 mark of this video:
http://www.nfb.ca/film/group_hunting_on_spring_ice_pt_1/
She is making a bowstring from sinew. Does it look like she is braiding the bowstring? I have seen several references to "plaited sinew" bowstrings being used by eskimo.
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I've used all sorts of material. Most of the time i use cheep polyester thread that's usually used for sewing. Each strand has a 2 lb breaking stength i generally use 40-60 strands depending on the weight of the bow (I haven't had a bow hevier than 50 lbs yet). I've also used floss, monofament fishing line, and even sinew and yucca bofore. I've mainly used the thread for it's ease of access, affordability, and workablility.
I normally wouldn't care about stretch or weight if i'm target shooting or if i wanted to hunt small or mid sized game, so thread works just fine. But i want to start measuing the velocities from bows and to get the best numbers I would need the most efficient string. I obtained Dyneema fishing line which is 0.18 mm at 20 lb test. From what i've looked up dyneema has a stiffness (modulous of elasticity) of around 100 Gpa, way higher than thread. If i wanted to use a natural material I'm leaning towards flax (linen thread), or hemp.
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I'm not sure that braided would stretch less than twisting. I would think it may be tougher to get even strain on the individual strands with a braided string.
It depends on how good your braid is. Most ropes are braided now days (granted they are 6-20+ hallow braid and not the simple 3 strand). But then again those are maid with machines and not by hand.
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What string material are you using? Do you pre-stretch your strings? I have a jig that stretches them tighter than when on a bow.
Yes pre-stretching helps a ton. Usually i just let the bow do it and re-adjust the knot. But even then i believe the twist will still have more stretch then the braid and especially the endlesss loop.
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Endless loop strings should still be twisted which does allow for some adjustment. (I put about 20 twists on most and 30 on long warbows)
It's easy to get strings the right length if you use a long string and an adjuster to find the right length first.
Del
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A twisted dyneema string won't stretch to any degree that you will notice.
Clearly twisted and endless strings work more than adequately. Braiding is just adding a whole level of unnecessary complexity.
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I think you should stop using the polyester thread and get something that is stronger. Get a couple spools of D97 and give that a try.
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gfugal, I've always used B-50.
I used to make endless strings and did put in a few twists.
Now, I make Flemish and let them pre-stretch before serving.
Just a little caveat...
A string should have 4x times the bow's weight for a minimum breaking strength (Baker, TBB2, P. 217).
So a string with 2# threads for a 40# bow should have 80 threads minimum.
I never did a braided line. I think it may increase string mass substantial. But can't say for sure.
These days I am happy with the Flemish twist. I wonder if Chubby Checker was a bowyer. :)
Jawge
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Yeah George, he was doing the twist way back in the 1960's. :OK Your comment probably went over lots of heads. ;)
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Pat, I know. :) Jawge
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Jawge,
Some of us were there! Even before "Rock Around the Clock"! Got to see Chubby live one time when I was in college in the early 70s. Btw, Happy Birthday to Me! I'm only 26(but it's the 3rd time around!)
Hawkdancer
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Happy Birthday, Hawkdancer. I just had my 67th on July 28. )P(
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Does anyone know what B-50 and D97 are made of? And what their modulous of elasticity?
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Happy Birthday, Hawkdancer.
I got to see some of those really good bands and performers.
I'm 69.
B 50 is dacron.
Jawge
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Does anyone know what B-50 and D97 are made of? And what their modulous of elasticity?
D97 is also Dyneema. Your fishing line is basically the same thing although it is braided itself.
B-50 Dacron is the brand name for a type of Polyester.
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https://en.wikipedia.org/wiki/Polyethylene_terephthalate yeah so the dacron is a type of polyester. It's got a Modulus of elasticity of about 3 Gpa. That's a lot smaller than the 100 plus Gpa of Dyneema. https://www.matbase.com/material-categories/natural-and-synthetic-polymers/polymer-fibers/synthetic-fibers/material-properties-of-dyneema.html#properties
Yeah, so I think I'll get me some D97 next time. Where do you find it?
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I use D97 Flemish twist and try to have no more than 3 twist per inch , that same number of twist also works very well with B 50, very little stretch, if you twist the a bunch to start or to adjust length it becomes a coil spring and really make a difference in arm slap and bow efficiency for me, also noise. ;) Happy birthday Hawkdancer !!! and it wasn't over my head either Jawges. ;) :)
Pappy
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So my brother is an engineer, and he said that the loops in an endless loop string aren't necessarily weaker than the main length of the string. We even did a test with string where we broke several strings that weren't served and they broke in other places and not the loop. That really surprised me. as soon as we closed the loop with serving though it would break where the angle changed. So yes the loop is a weak spot but not because it appears to have half the material, but because closing the loop with serving causes an angle change with changes the forces. Therefore if you make your endless loop based on the main section strength and not the loop strength then you shouldn't have any extra mass, you would actually reduce mass. Therefore I think I've come to the conclusion that endless loop would be the best method if you're going for optimal performance as long as you keep it waxed and avoid snags. But depending on your purpose Flemish twist or other methods would do perfectly fine, especially if you are using an extremely stiff material like Dyneema. Also, Flemish twist will always have its place in natural plant fibers since you can't splice in threads of shorter length to make a longer string with an endless loop.