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Crossbows (Read 12416 times)
johan
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Re: Crossbows
Reply #15 - Sep 10th, 2016 at 1:12pm
 
im not there yet but at what strength should i make the bowstring? is there a way to determine the strength?
the bows i've made so far have linen bowstring but they have low draw weights...
i'll make a dacron/dyneema bowstring for the crossbow and i want to:
- keep the diameter of the bowstring less than 6 mm
- be safe at 400 # or maybe more .
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Onager Lovac
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Re: Crossbows
Reply #16 - Sep 11th, 2016 at 2:21am
 
Hello Parmenion, on ¨The Book of the Crossbow¨ by Sir Ralph Payne-Gellwey, he states that the bowstring should stand 20 times the final draw weight of the crossbow, we in the crossbow community don´t really follow his advice, 8 to 12 times the final draw weight is good enough, a strand of B50 Dacron has 50 pounds of strength per strand/thread so assuming you want to make the string strong enought to withstand 8 times the strength of your bow (3200 pounds) you would need 54 strands of B50 Dacron.
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johan
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Re: Crossbows
Reply #17 - Sep 11th, 2016 at 9:28am
 
wow that needs to be a huge diameter! almost an inch ?!
i ll probably need to make the nut a little bigger and the string less than 8 times stronger... i hope it will not break on me.

what diameter do you have on your strongest crossbow?
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Bill Skinner
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Re: Crossbows
Reply #18 - Sep 11th, 2016 at 2:17pm
 
I've never made a 54 strand bowstring but I have made some 18-20 strand strings.  They were around 2 mm to 2.5 mm.  So a 54 strand string made from Dacron or Dyneema should come in at about the 6 mm mark.  You may want to look more at Dyneema, Dacron tends to stretch some when you first put it on a bow.

Is your string going to touch the top of the cross bow?  If it does, that will cause most of your wear.

And the bolt for a 400 pound crossbow is going to be pretty thick.
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johan
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Re: Crossbows
Reply #19 - Sep 12th, 2016 at 2:23am
 
oh yes you are right i counted something wrong Tongue

the string will touch the top of the crossbow so it needs protection there, which is gonna raise the diameter a little.
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