Author Topic: String length/ brace height  (Read 370 times)

0 Members and 1 Guest are viewing this topic.

Offline DC

  • Member
  • Posts: 4769
String length/ brace height
« on: November 13, 2017, 10:00:44 am »
I just made a string for a new bow. It's a little short. I was curious how much too short but I didn't know of any relationship between string length and brace height. I braced my regular shooter and measured the brace height. It was 5". Then I wrapped the string once around a 1/8" wire which shortened the string by about 3/8". The brace height went up to 5 3/4". So this is a 2:1 relationship. At least for this bow. Do you know if this relationship holds true for most bows or does it vary quite a bit?
Vancouver Island

Offline BowEd

  • Member
  • Posts: 5860
Re: String length/ brace height
« Reply #1 on: November 14, 2017, 02:52:09 pm »
I usually make a string as long as what my tillering string was.
Beadman
You got to stand for something or you'll fall for anything.
Ed

Online Badger

  • Member
  • Posts: 6103
Re: String length/ brace height
« Reply #2 on: November 14, 2017, 02:58:04 pm »
  A string 3" short will usually give you about a 6" brace so that sounds about right. I just twist mine up or down to where I want them. You don't have to get them right on the money.

Offline DC

  • Member
  • Posts: 4769
Re: String length/ brace height
« Reply #3 on: November 14, 2017, 03:05:43 pm »
  A string 3" short will usually give you about a 6" brace so that sounds about right. I just twist mine up or down to where I want them. You don't have to get them right on the money.
To answer the question on my other thread, how much can you change the length by twisting it?
Vancouver Island

Online Badger

  • Member
  • Posts: 6103
Re: String length/ brace height
« Reply #4 on: November 14, 2017, 03:40:32 pm »
  A string 3" short will usually give you about a 6" brace so that sounds about right. I just twist mine up or down to where I want them. You don't have to get them right on the money.
To answer the question on my other thread, how much can you change the length by twisting it?

  You can twist it up 3 or more inches if you like, best to stay within an inch or so but no difference in the way the bow shoots if you twist it up 3". I do it all the time.

Offline BowEd

  • Member
  • Posts: 5860
Re: String length/ brace height
« Reply #5 on: November 14, 2017, 09:39:11 pm »
Dc....Yes what Steve said there.The same string can be used on different bows.I do that here too.
Beadman
You got to stand for something or you'll fall for anything.
Ed

Offline Ryan Jacob

  • Member
  • Posts: 40
Re: String length/ brace height
« Reply #6 on: November 14, 2017, 10:51:50 pm »
Hope this wonít be too confusing...
Iíve found that this is the formula:

Brace Height= ((ntn length - string length) X 2) - (string length X %stretch)

In real words, the brace height is the difference of ntn length and string length, and accomodate for stretch... now that I think about it, itís probably still confusing.

Offline Del the cat

  • Member
  • Posts: 6661
    • Derek Hutchison Native Wood Self Bows
Re: String length/ brace height
« Reply #7 on: November 14, 2017, 11:16:57 pm »
Hope this wonít be too confusing...
Iíve found that this is the formula:

Brace Height= ((ntn length - string length) X 2) - (string length X %stretch)

In real words, the brace height is the difference of ntn length and string length, and accomodate for stretch... now that I think about it, itís probably still confusing.
That's like a damn maths question.
Rearrange the following equation to give sting length! sheesh!
I'll have a go.
let brace height=b, ntn length = n, string length = l, % stretch = s

b=(n-l)x2 - lxs
therefore b=2n-2l-ls
therefore b=2n-(2-s)l
therefore (2-s)l=2n-b
and finally, therefore
l=(2n-b)/(2-s)     ta da!

Errrr so... hmmm if I can remeber what the letters all stood for  ::)

string length=2x ntn length-brace height divided by 2x %stretch

Not sure if it's any help or even correct, but it exercised the old grey matter  :)
Del
PS Ryan, do I get paid for doing your homework ;)
« Last Edit: November 14, 2017, 11:21:13 pm by Del the cat »
Health warning, these posts may contain traces of nut.

Offline Ryan Jacob

  • Member
  • Posts: 40
Re: String length/ brace height
« Reply #8 on: November 15, 2017, 01:40:16 am »
 It is close enough from my experience, also makes sense (math wise), now do you want the payment per hour or per problem  >:D... Actually gonna stop now pretty sure a moderator or admins gonna get mad if we keep discussing payments :-X
« Last Edit: November 15, 2017, 01:43:26 am by Ryan Jacob »

Offline Del the cat

  • Member
  • Posts: 6661
    • Derek Hutchison Native Wood Self Bows
Re: String length/ brace height
« Reply #9 on: November 15, 2017, 02:06:47 am »
Will work for kitty treats  ;D
Del
Health warning, these posts may contain traces of nut.

Offline Hawkdancer

  • Member
  • Posts: 761
Re: String length/ brace height
« Reply #10 on: November 15, 2017, 09:05:44 am »
 >:D, what's the old standby rule of thumb, 3" short for straight bows, 4" short for recurves, of ntn,  then adjust to suit your bow? :BB >:D(no string maker emoji)!  Not being real sharp on string/bow making, I try to match the old string and go about an inch shorter to account for stretch.  Also get brace height a bit more than fletch length for clearance.  No formula, I flunked math! >:D
Hawkdancer

Offline Ryan Jacob

  • Member
  • Posts: 40
Re: String length/ brace height
« Reply #11 on: November 15, 2017, 09:43:42 pm »
Del
I think you actually screwed up on the first bit,
That's like a damn maths question.
Rearrange the following equation to give sting length! sheesh!
I'll have a go.
let brace height=b, ntn length = n, string length = l, % stretch = s

b=(n-l)x2 - lxs
therefore b=2n-2l-ls
therefore b=2n-(2-s)l
therefore (2-s)l=2n-b
and finally, therefore
l=(2n-b)/(2-s)     ta da!

Errrr so... hmmm if I can remeber what the letters all stood for  ::)

string length=2x ntn length-brace height divided by 2x %stretch

Not sure if it's any help or even correct, but it exercised the old grey matter  :)
Del
PS Ryan, do I get paid for doing your homework ;)

The formula should actually look like this (using your symbols) :

b= ((n-l)x2) - (lxs)
b= ((n-l)x2) - (ls)

Thatís for brace, you cant multiply 2 to (n-l) until you actually plug in the numbers (at least when you actually will put numbers instead of letters)

for string length...

l= ((n x (b/2)) + (lxs)

Good Luck with these, >:D, Iím not doing anymore math, my heads starting to hurt ;D


Offline Del the cat

  • Member
  • Posts: 6661
    • Derek Hutchison Native Wood Self Bows
Re: String length/ brace height
« Reply #12 on: November 15, 2017, 11:08:44 pm »
@ Ryan
"you cant multiply 2 to (n-l) until you actually plug in the numbers (at least when you actually will put numbers instead of letters)"

Errr, Sorry but yes you can, it's basic algebra it works regardless of plugging in letters, numbers or scraps of old deer skin.
2(a-b) expands to 2a-2b

Not the place for a maths debate, mind there are some maths debaters on some forums ;)
Del
PS. If You can find any numbers for a and b that won't work I'll pay £50 £100 to the charity of your choice!
« Last Edit: November 15, 2017, 11:39:04 pm by Del the cat »
Health warning, these posts may contain traces of nut.

Offline Ryan Jacob

  • Member
  • Posts: 40
Re: String length/ brace height
« Reply #13 on: November 16, 2017, 05:23:47 am »
Got it, what did I expect Iím in high school ::) ... maybe I screwed up the first equation... wait, sorry, I read your math wrong :-[