String length vs. change in brace height?

[McDave]

I made a first pass at a new string and the brace height was 1 1/2” too low, with what I consider to be an adequate amount of twists to hold the string together but allowing for more twists later on as the string stretches. How much shorter should I make the next string so that I can eliminate the too low brace height (or maybe make it a little short to allow for initial string stretch) without having to add more twists to the string?  Somehow I don’t think there is a 1:1 correlation between changes in string length and changes in brace height.

[Wudstix]

 

[artifaker1]

This is a great subject for me to, very interested in responses, I do have trouble getting the lengths right ... I can't really tell you anything you don't already know .... so the length of the bow and string material. I've found that certain brands of bows don't take a standard length... like say pronghorn longbows take a different length, which if I remember right is longer, all of the morrison ILFs take 3 inches shorter whether recurve or long bow and so on. Do you have the old string to compare to the new too long string? This could help with guessing .....
I could measure some of my strings that are finished of course, that might help if the brand is one that I have made strings for .... which are the above mentioned and also black widows and older bear stuff ...

[McDave]

This is an old Bill Price longbow that I found at a garage sale.  It doesn't have a string.  It measures 73”, nock to nock.  My string jig won't make a string that long, so I had to improvise and double back more times than you normally would.  I was surprised it came out as close as it did, really.  I don't know how many times I want to shoot it, and maybe it will break on the first try.  But Bill Price was a good bowyer, and I would like to see how it shoots at least once.  I will unravel one of the loops on the string I made and shorten it some, but that is a tedious process, and I don't know if I have the patience to do it more than once.

[McDave]

i'm just guessing on brace height. I think a longbow of that length would have a brace height of 8”, and the string I made gave it a brace height of 6 1/2”.

[Orion]

I dunno.  I think a brace of 6 1/2 inches might be pretty close to what it should be.  Regardless, if you open one loop and shorten the string about 3/4 to one inch, it should get you close to 8 inches at brace.  I do this by feel, and I've never done it for a bow that long, but I think it will get you in the ballpark. 

[Even]

My longer longbows (70", 72") seem to like brace heights around the seven inch mark, plus or minus a bit.  I'd try it just over seven, wouldn't give you too far to go.

[McDave]

I think you're right. A modern longbow of 73”, if there are any, might go to an 8” brace height or even higher, but it appears that this bow was made to be a replica of the target longbows made in the late 1800’s, early 1900’s. It has two laminations, and no fiberglass, as far as I can see. It has horn nocks. In all the photographs I can pull up of that era, the loong target longbows seem to be braced lower than we would like today. So I will aim for 7-7 1/2”. I suppose they were made so long because they had no fiberglass, so a long longbow would probably last longer than a short longbow, since the limbs would bend less. Of course, one would think that performance would diminish accordingly. We'll see (if it lasts that long).

[Terry Green]

I didn't read all the replies but did you consider twisting it up to the right brace height and then measuring it again so the next time you'll have the correct measurement?

[McDave]

Excellent idea Terry.  Why didn't I think of that?

[McDave]

Using Terry's method, which is so obvious it embarrasses me that I didn't think of it myself, shortening the string I made by 1” increased the brace height by 1 1/2”.  I'm not sure if this is a general rule, or unique to this bow.  Putting enough twists in the string to decrease the length by 1” was excessive, in my opinion, especially considering that more twists would have to be added as the string stretched in use, but it gave me the information I needed to know.

I think that initially, I’ll use the string I already made, and just untwist it until the brace height is 7”, as that seems more consistent with bows of that era.  I'll exercise it a bit before I try to shoot it, and keep my fingers crossed.

[Orion]

Good it worked for you.  I don't know if I'd call it a general rule, but as I noted above it generally works for me. 

[Even]

Good luck, McDave... hopefully it holds together.  I think it will.  I have a couple old longbows here from the twenties, and they're still shooting great.  One, I had to reglue the riser back on when it cracked, but after that it has been the best of the bunch.  My GF shoots it regularly, and loves it.

[charles m]

No sweat McDave, forest for the trees, we've all done it from time to time. 

[Walt Francis]

Dave,
To find the best brace height try the following the instructions below, it is how I have tuned all my bows for over 30 years.
Try starting with a low brace height (6 3/4”) and shoot several arrows. Then twist the up a 1/4”, shoot another 6-12 arrows, and note any difference in hand shock, loudness, and string vibration. Then do it again. Repeat until the the vibration and noise gets quietest, then starts getting worse. Then start untwisting, re-twisting, until you find the sweet spot.  I usually go past the sweet spot both directions several times before getting it right.

This will also stretch a B-50 string enough to provide an accurate length.

Adcock posted a method really close to what I do on Tradgang around 2003-2006, It might in the how to forum.  Let me know if you cannot find it or have questions. 
I can PM you a copy if you would like.

[Mo_coon-catcher]

I cheat and make my initially strong with an adjustable rat tail string to easily define the proper brace by adjusting the knot. Once you have the brace height down, then you know exactly how long the string needs to be. I’m betting a brace height of around 10% of the bow length will be around where you’ll end up as a happy spot. I like to make longer Victorian style english longbows and they usually end up braced around 6.25-7”with a D97 string.

Kyle

[McDave]

Kyle,

Using an adjustable string, like a tillering string, would be another good alternative, as you suggest.

I'm surprised that you use D97.  Do you reinforce the tips to allow for the lack of stretch in D97?

[Mo_coon-catcher]

I really only mess with wood bow and use overlays and horn nocks but they’re not really necessary. While shooting in I’ll cut temporary side nocks in while the tips are still fat and tweak how they’d shoot before cutting down to size and applying overlays or horn nocks. Even up to 100# draw I havnt had any problems.the tips are more for pretty than anything with properly cut side nocks.

Kyle