Bracing height and string length


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From: mvapldrn@dutlsb3.lr.tudelft.nl (Marcel van Apeldoorn)
Subject: Re: Bracing height and string length
Date: 30 Oct 1995 12:11:08 GMT

bmb5meb@biovax.leeds.ac.uk wrote:

> I've finally got round to getting my bow tuned now that I've got the right
> length/spine of arrows, but I've noticed a bit of a problem with my bracing
> height. I have a 70" Samick Progress II recurve which should be braced to
> 8 and a quarter to 9 inches to the throat of the handle, but even with
> around 50 twists in my string, my bracing height is still only 8 and seven
> sixteenths of an inch. I have measured my string as being 66" in length
> (this confused me since I thought it should be 70"). Is this a reasonable

No, the 70" stands for the length of the bow (tip to tip) measured along the outside of the limbs and handle (so not in a straight line!!)

I think 50 twists is quite a lot, when your string starts to curl up (or something, you know what I mean when you see it) when its not under tension, then there are too much twists in it. Because during the shot, there comes a moment that the string is not under tension (sounds strange, but its true, I even photograped the moment) and at that moment, the string will try to curl up, and immediatly after that will be stretched again, this will reduce the life-span of your string.

> length for a 70" bow or is it too long?
> I have also noticed that I have quite a lot of string in contact with the
> recurve at the tips of the limbs. Does anyone who has used/seen this type
> of bow know if this is normal.
> Any help would be gratly appreciated.

IMHO !!!!!

There are several ways of finding the correct brace-height, the problem with _ALL_ methods is that when you have your bow properly tuned for the specific brace-height you shoot, then an increase or decrease in brace height will affect your tune. The dynamic spine of the arrow will change when you lower or raise your brace-height. So it is important to try and get your brace-height correct _before_ you fine-tune your bow.

One method you can use is to go to a long distance were your groups are still nice and tight (e.g. 50m perhaps 70m) and start at the lower end of the manufactorers recommendation. Shoot some arrows (e.g. 18) and chart the _vertical_ position of each arrow. Raise your brace-height slightly (e.g. 1/16 or 1/8 inch at a time) and again shoot some arrows. Also make a mental note of the noise the bow makes, or ask someone else, because you're too busy shooting and you shouldn't be paying attention to anything else but making one good shot (each time). Keep raising your brace-height until you are at the max. recommended brace-height. KEEP YOUR SIGHT ALWAYS THE SAME.

This could happen (and usually happens to me at 50m); When you start at the lower end, the arrows hit somewhere on the target, raising the brace-height will probably make the arrows hit a bit heigher than before, raising the brace-height a bit more will reduce the effectiveness of the bow, and the arrows will start to hit lower on the target.

My graphs look something like this;
 [cm] |
      |      |   | 
      |  |           |   |
      |                      |
      |                          |
      |
      +-----------------------------------------
                                brace-height ->

NOTE: It is VERY important that you check your nocking point each time, and make sure that it is the same. Because raising and lowering your brace-height could have an effect on your nocking point (the effect increases when your tiller difference increases)

I usually choose the brace-height that gives me the highest groups on the target, because (and this is my theory) it means that the energy-transfer from bow to arrow is at its maximum. The energy that is left behind in the bow, and produces the sound AND vibrations at this point is at a minimum. This brace-height doesn't necessarily give me the tightest groups, but thats because the bow is slightly out of tune when you change the brace-height. When I've found the correct brace-height I'll re-tune my bow (usually only fine-tuning is needed). Sometimes I change my brace-height slightly (no more than 1/8 of an inch) to try and get a better tune (both horizontally and vertically) but I think its possible to do this with the button or rest also.

Anyway, this is what I do (sometimes) it works for me, but as with everything else in archery it doesn't have to work for you.

Happy shooting,

-Marcel van Apeldoorn

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From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Bracing height and string length
Date: 31 Oct 1995 10:21:43 GMT

mvapldrn@dutlsb3.lr.tudelft.nl (Marcel van Apeldoorn) writes:

>bmb5meb@biovax.leeds.ac.uk wrote:
<Some stuff which I've snipped>

>No, the 70" stands for the length of the bow (tip to tip) measured along
>the outside of the limbs and handle (so not in a straight line!!)

Indeed it does but I bet you one manufacturers 70" will be different from anothers! 8) This is, I hypothesise, due to the fact that most manufacturers actually work in mm rather than inches.

>I think 50 twists is quite a lot, when your string starts to curl up
>(or something, you know what I mean when you see it) when its not under
>tension, then there are too much twists in it. Because during the shot,
>there comes a moment that the string is not under tension (sounds strange,
>but its true, I even photograped the moment) and at that moment, the string
>will try to curl up, and immediatly after that will be stretched again,
>this will reduce the life-span of your string.

Cool any chance of posting the picture? Again I'll agree with the above but a string is only too twisted if it begins to knot up as you twist it. As I said before if it goes smooth and round when braced then it's fine. Basically the strands have to run more vertically than they do horizontally or you get this tension loss which Marcel has described.
The more you twist the string the more the strands tend towards horizontal.

<Snip...Help....my brace height is pox>

>IMHO !!!!!

Or even IMO, since he ain't that humble 8)

<Snip, brace height effects tuning>

>One method you can use is to go to a long distance were your groups are still
>nice and tight (e.g. 50m perhaps 70m) and start at the lower end of the
>manufactorers recommendation. Shoot some arrows (e.g. 18) and chart the
>_vertical_ position of each arrow. Raise your brace-height slightly
>(e.g. 1/16 or 1/8 inch at a time) and again shoot some arrows. Also make
>a mental note of the noise the bow makes, or ask someone else, because
>you're too busy shooting and you shouldn't be paying attention to anything
>else but making one good shot (each time). Keep raising your brace-height
>until you are at the max. recommended brace-height. KEEP YOUR SIGHT ALWAYS
>THE SAME.

This is interesting, I like the logic behind it too although I'd never seen it written down quite like this!

My graphs look something like this;

<Marcels marks = |, my marks = *>
 [cm] |                         *  
      |      |   |          *     *
      |* |      *   *| * |          *
      |    *                 |
      |                          |
      |
      +-----------------------------------------
                          MaxBH ^       brace-height ->

Right enough I shoot my bow at maximimum bracing height because it's quietest and smoothest there! As always different manufacturers and even different limbs from the same manufacturer will want to brace at different heights. I'm bracing my bow at 9 3/4" and I guess Marcel is bracing his at somewhere around 8 3/4", both 70" bows! His string is probably at least 1/2" longer than mine!

<Snip, re-tuning after changing BH>

>Anyway, this is what I do (sometimes) it works for me, but as with everything
>else in archery it doesn't have to work for you.

I do like this and it make sense, maybe we should include it as a suggestion for the FAQ??? Any thoughts anybody?

I'm looking forward to getting back some distance ie more than 18m to give it a go in the real world 8)

John Dickson,(aka Stretch)

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From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Bracing height and string length
Date: 3 Nov 1995 10:38:32 GMT

melin@cm5cofis.gmd.de (Stephan Melin) writes:

<Snip, Marcels stuff>

>Now for my {ignorant} question {after all I am a real crap shot at the
>moment ;-( } :
>Doesn't the correct position of the nocking point also depend on the bracing
>height?

Probably but how much? What are the main factors that influence your nocking point? Ok it varies a lot from archer to archer, but mine are bow tiller and finger position on string (and nock type but we'll assume that's constant!)

You're finger position shouldn't change with change in bracing height, so I guess we can assume that's fairly constant too (although unless your name is Simon Fairweather perhaps not as constant as your nocks!)

So it's mainly down to tiller changes. How much does your tiller change when you change the bracing height? As far as I'm aware mine doesn't change, if it does it's too small to measure using a bracing guage. The distances change but the difference doesn't.

So Marcels test seems valid for me.
BUT then bracing height affects the energy imparted to the arrow. So you may get very high arrows (sight mark) on a very low bracing height which perhaps isn't the best BH for your bow...it just imparts a lot of energy because it's in contact for longer. In which case you have to rely on noise, vibration and accuracy to tell you about your BH!
So as usual the tuning test that works for one person may well not work for another!

As usual all IMHO and may well be right, wrong or indifferent,

John Dickson,(aka Stretch)

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From: "derek a. zelmer" <zelmeda4@wfu.edu>
Subject: Re: Re:Brace height and string length
Date: Thu, 2 Nov 1995 07:56:52 -0500

On Wed, 1 Nov 1995, George Stoneberg wrote:

>> On Flemmish twist strings; I have heard from some longbow archers that they
>> tend to slip and need constant re-tightening, though I'm not sure if this was
>> just the archers in question. I've seen Flemmish twist strings being made,and
>> it's really impressive how quick and easy they are to do. I must learn that someday...

> I learned by buying a video tape from
> Yellowstone Archery (208)529-8506. There's probably someone over there that
> puts out something similar.

Awhile back there was an excellent article in Traditional Bowhunter on making the Flemish twist...complete with instructions on making a jig to use. It's ahrd to explain, but easy to do. I could post it if you'd like.

- Derek Zelmer
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From: David Bruce <dib@dra.hmg.gb>
Subject: Re: Bracing height and string length
Date: 3 Nov 1995 13:31:01 GMT

jdickson@festival.ed.ac.uk (John Dickson) wrote:
>melin@cm5cofis.gmd.de (Stephan Melin) writes:
>>Doesn't the correct position of the nocking point also depend on the bracing height?

>Probably but how much? What are the main factors that influence your
>nocking point? Ok it varies a lot from archer to archer, but mine are
>bow tiller and finger position on string (and nock type but we'll assume
>that's constant!)

I assume that Marcel changes his bracing height by twisting the string. When you do this the nocking point is going to stay the same proportion above centre, but not necessarily the same distance. (I've not measured it, but I guess this is a fairly small effect. Nevertheless, it might be significant, which is why Marcel said to check.)

David Bruce

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From: jdickson@festival.ed.ac.uk (John Dickson)
Subject: Re: Bracing height and string length
Date: 3 Nov 1995 15:02:38 GMT

David Bruce <dib@dra.hmg.gb> writes:
>jdickson@festival.ed.ac.uk (John Dickson) wrote:
>>melin@cm5cofis.gmd.de (Stephan Melin) writes:

>>>Doesn't the correct position of the nocking point also depend on the bracing height?

>>Probably but how much? What are the main factors that influence your
>>nocking point? Ok it varies a lot from archer to archer, but mine are
>>bow tiller and finger position on string (and nock type but we'll assume
>>that's constant!)

>I assume that Marcel changes his bracing height by twisting the string.
>When you do this the nocking point is going to stay the same proportion
>above centre, but not necessarily the same distance.
>(I've not measured it, but I guess this is a fairly small effect.
>Nevertheless, it might be significant, which is why Marcel said to check.)

Now that's a completely different way of looking at what Stephan said! I assumed he meant the correct position for your nocking point may change eg if you shoot off 9" your n-pt may be 6mm above square (when tuned); if you shoot off 9.5" your n-pt may be 4mm above square when tuned.

My n-pt moves up about 0.5-1mm when I move from minimum b-H to maximum B-H (9.25" - 9.75"). So not much, and thats with a string that is maybe a bit too twisted at the top of the range.

You are certainly right to emphasise the point that if you are going to use Marcels test you must make sure you check the n-pt each time you change the B-H.

(BTW when I say *factors which influence your n-pt* I mean where you put your n-pt when the bow is tuned)

John Dickson, aka Stretch


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