String length vs brace?

[Petros]

OK folks, searched and searched and must be wording it wrong.

So I'm waiting on a string from Northern Mist for for recent acquired Baraga. In the meantime I can only look at and study it. It is actually 64' nock to nock, but the string that came with it is 61.5" as measured strung on bow in pic to top of loops. Should be close by that 3" shorter rule of thumb, but untwisted still yields a brace height of 7 1/8" which is too high by 3/8-5/8ths.

Question is: what's the general rule for increased string length lowers brace by X amount?

I did twist 10 times which shortened overall length by 1/4" and seem to increase brace by 1/8". But with such small variances it's tough to tell for sure.

Thanks, all, sure hope I worded this right.

 

[Orion]

There is no rule of thumb for that.  You twist, or untwist, a few turns and measure.  Depends a lot of string material, number of strands, bow length, bow design, etc.  Just play around with it until you get a brace height that shoots well for you.  

Generally AMO string length is three inches less than the bow's stated length, i.e.,61 inches for a 64-inch bow, but actual string length needed can vary by a half-inch or more either way depending on bow design.

[Petros]

Guess a person would ultimately just have to try a few out. Maybe I'll knot up an old 68" string until target BH is achieved and go by that in case new string goes mia.

Kinda funny my Great Plains is listed as 64" but is really 63" nock to nock and Northern Mist is 64" as labeled. That GP bow has a 61" string in it's twisted strung Length. This it's what got me wondering about the 3" shorter rule for longbows. And to add more confusion, I stumbled onto a Canadian forum in which most of the people said 3"shorter was to high a BH for their bows.

[WESTBROOK]

Have ya shot it since untwisting it... it'll come down some more.

Steve didnt make that string, a previous owner probably had it made for a specific length for where he liked the bow braced.

Eric

[Petros]

Not shot it yet. Almost no twist in it at all. I'm pretty sure it's after market string.

[McDave]

If the string that came with the bow is new, I'm pretty sure it will stretch and drop your brace height by the 3/8 - 5/8" you need within a hundred shots or so.  OTOH, if it has been previously shot in, it may not stretch that much.  Starting with a BH that is 3/8 - 5/8" high doesn't seem that extreme to me, and I wouldn't be afraid of shooting it if it is otherwise sound.  When I make a new string for a bow, it starts out that high and stretches to the correct BH or even longer so I have to add a few twists by the time I get back from my first day shooting it.

[tracker12]

Did you consider calling the bowyer and asking his the corret lenght for the bow?

[Petros]

Alright then. New string, straight from Steve himself arrived yesterday and I got to test drive the new to me bow. Turns out his new string is a bit longer than the used stretched one that came on the bow. I put it on and let it set for awhile with a few draws in the meantime and presto, it came in exactly at his recommended starting BH of 6.5". So I guess that 3inch shorter than AMO length rule of thumb certainly doesn't apply in all cases.

Anyhow, bareshafted, paper tuned, and fletched  some arrows up and headed to the club. This bow is now my favorite bow I own. Not sure exactly what the best feature is, but can say for sure that the grip shape for my hand wins hands down.

[Sixby]

Most times when I build a bow dead on notch to notch I start with a two inch down string and it twists right up to my 7 1/4 brace. Sounds like this bow of yours is same way. Amo would require the bow to be shorter to make the 64 in amo measurement of three inches down. Actually it would be a bow that measured 63 inches but because it uses a 61 in string twisted up a bit would be called a 64 in bow. I just build my bows 64 inches and use a 61 1/2 in string most times or a 62.
As long as you get the bow to a good brace and have good stability and shootability without overtwisting the string I don't see how it matters.

God bless, Steve

[SlowBowinMO]

Originally posted by Petros:
Alright then. New string, straight from Steve himself arrived yesterday and I got to test drive the new to me bow. Turns out his new string is a bit longer than the used stretched one that came on the bow. I put it on and let it set for awhile with a few draws in the meantime and presto, it came in exactly at his recommended starting BH of 6.5". So I guess that 3inch shorter than AMO length rule of thumb certainly doesn't apply in all cases.

Very common for custom longbows, the 3" shorter than AMO should apply but often it doesn't in actual practice.  One well known custom make needs a string only 1" shorter than its marked AMO length to brace properly.

Not a big deal though once you know the length your set.

Rarely run into this scenario with custom recurves though, not sure why but we don't.

[LBR]

Lots of bows aren't marked by AMO.  If they were, then a a string 3" shorter (measured under tension) would put it at proper brace. AMO doesn't go by the bow's physical length but rather the string that fits it properly.