string length and more

[morganp]

This is one part of archery I have not explored, I send off my old strings when I need replacement or spare.

I know I like a softer string and low poundage and prefer to finesse my shooting with arrow tuning, but I thought I would have a go at making a string. I have made twisted strand strings from hemp and nettle and jute but never properly with modern materials. I just used common-sense and trial and error and shonky knots etc until they worked.

I have found tutorials on Flemish twist but so far none of the tutorials I have seen covered the very basic, measuring for length! They assume you know that. How do you do this for longbow or for recurve? For example, length between nocks is 'x' then to get brace height 'y' ...

Also, is there a formula chart anywhere for poundage against number of strands for different materials? Modern, consistent materials that is?

Thanks.

[longbow steve]

http://www.ozbow.net/phpBB3/viewtopic.php?f=34&t=8573
This is a build along that Jeffro did, there is also another in the Traditional; crafts section as a sticky thread. Cheers Steve

[morganp]

http://poorfolkbows.com/flemish1.htm linked to in thread, much easier and includes the poundage.

What happened to Coach? He was a good bloke once you got past the BS and stood up to him.
So many good people gone.

[matt61]

When I used to make them before I got the string jig, if my memory serves me right I used to cut the strands as long as the bow you are making the string for plus fourteen inches ie 62 inch bow plus fourteen = 76" long strands. I do have it written down some where, will try and find it. I have made a string in the bush using two tent pegs nocked into a log using that method by wrapping the string strands around the pegs set at 38" and then cutting it at one peg which then gives you a 76" bundle. Don't crucify me over the 14" that could be wrong, old age is setting in
cheers
Matt

[littlejohn59]

hey there morganp
String length for a recurve is 4" shorter than the length of the bow. If your bow is 66" your string needs to be 62"

if your bow is 20-30# you need the string to be 8 strands
30-35# you need the string to be 10 strands
35-45# 12 strands
45-55# 14 strands
55-80# 16 strands

[littlejohn59]

oops i forgot to say 3" shorter for a longbow

[morganp]

Thanks everyone! There's a starting point or two then. I'll try to make a proper linen string first because I have some and then try some modern materials. I have seen a few variations on the length calculations but I can always redo it if wrong for my bows.

[rmcpb]

The jig pattern used on Poor Folks Bows is great. Always worked for me.

[GrahameA]

Morning.

... I have found tutorials on Flemish twist but so far none of the tutorials I have seen covered the very basic, measuring for length! They assume you know that. How do you do this for longbow or for recurve? For example, length between nocks is 'x' then to get brace height 'y' ...

Suggestions.

a) For an existing bow - Measure the "Nock-to-Nock" length of a bow. Then measure the String length for the same bow. Compare them. If you do this for several bows then you will have the relationship.

b) If you want the string length for an existing bow:

i) flex the Bow to give the required "Brace Height" (use a tillering setup is the easiest), measure the straight distance between the Nocks to get a String length.

ii) make an adjustable string, use it to flex the Bow to the desired Brace height, measure the length.

[rodlonq]

I have found what Littlejohn said for length is about right for the bows I have measured.

I have found tutorials on Flemish twist but so far none of the tutorials I have seen covered the very basic, measuring for length! They assume you know that. How do you do this for longbow or for recurve? For example, length between nocks is 'x' then to get brace height 'y' ...

What hasn't been said is there is no absolute measurement for what length 'x' will give brace height 'y' except maybe for a particular bow with particular string materials. The beauty is, the string length is quite variable for flemish twist strings. Fine adjustments can be made by twisting up or untwisting the string to achieve a range of brace heights for a given bow.

In addition to the "rules of thumb" for string length,(i.e. NTN - 4" for recurve and NTN - 3" for longbow). I start out with my string bundle overall length 20" longer than the required string length. My loops start 9" from the end. Once the loops are done I twist up the string until it is the nominal length (say 65" for a 68" NTN longbow) and try it on the bow, and fine tune it from there.

If all else fails, get yourself a copy of a DVD called "Doing the Twist". I found it invaluable because I learn much quicker by seeing than reading or listening. I ended up using a method that is somewhere between the two methods shown in the DVD.

Cheers.... Rod

[morganp]

I was thinking a mathematical formula would exist as a braced 'bow' is generally a portion of a circle diameter and the string is a 'chord'! Pi D for a circle 'x', allowing for brace height 'y' ... But rule of thumb is fine as timber varies. And curves vary especially when you include reflex and deflex. So, one twist per inch allows a fair bit of tweaking!

[rodlonq]

There is a formula Morgan, but you need to know more than the arc length (i.e. NTN) and required brace height. You also need to know the radius of the arc and the included angle between the ends of the chord and the centre of curvature. Neither of these are easy to measure with sufficient accuracy. As you say, any variation in bow shape away from a perfectly circular arc at brace height is going to make the result incorrect anyway.

If you really must know the length of the string exactly (say to make an endless loop string) you can use a tillering string that has a loop in one end and a bowyers knot in the other end to find your string length at brace height. Or you van use a longer string on a tillering stick and measure between the nocks when the brace height is right (using a string line to find the brace height).

6HalfInchBrace.jpg (52.47 KiB) Viewed 4217 times

Cheers... Rod

[GrahameA]

Hi Rod.

... If you really must know the length of the string exactly (say to make an endless loop string) you can use a tillering string that has a loop in one end and a bowyers knot in the other end to find your string length at brace height. Or you van use a longer string on a tillering stick and measure between the nocks when the brace height is right (using a string line to find the brace height). ...

Exactly. I would give you some rep if the system handled it.

[morganp]

I always over-complicate matters. Thanks folk. Easy, peasy. Now to find some nails to hammer into the dining room table ...

[Dennis La Varenne]

MorganP,

My old formula which I used to demonstrate at the old Longbow musters was BOW LENGTH plus TWO HANDLE LENGTHS. I used this for longbows Bowlength refers to the AMO length as measured along the back surface of the bow from nock to nock plus 8 inches. So a string for a 68 inch longbow required individual strands of 76inches.

When I used non-stretch material, I made the individual strands to AMO BOW LENGTH plus 1 inch, plus 8 inches.

If I made a string for a recurve from Dacron, I used the AMO BOWLENGTH minus 1 inch (to allow for higher brace height), plus 8 inches (as for a longbow). A recurve string made from Fastflight material or similar non-stretch material was made AMO BOWLENGTH plus 8 inches.

The 8-inch additions to the AMO BOWLENGTH allows for enough string material to form the Flemish twists at both ends.

When first mounted on the bow and braced, the brace height is always far too high, but the twists in the body of the string will lengthen somewhat and the brace height lowers itself and settles. Dacron stretches far more than non-stretch materials before it settles. I have always let the string settle on a braced bow, but some do it by hanging a heavy weight from the built string so long as it is prevented from untwisting.

When I was demonstrating at the Longbow Musters, I organised the lesson so that students could easily measure up a string whilst out hunting and did not have a string jig of any kind with them, so I taught that one simply measured an individual strand along the back surface of the bow plus another length of two longbow handles or two hands breadth. Then the other strands were cut to the same length from the reel. It worked out OK and could always be twisted up tighter to increase brace height if necessary.

The required number of strands was based on 6 times the draw weight of the bow's AMO draw weight. It is a good rule of thumb. The non-stretch material often has a breaking strain of 100lbs and Dacron is around the 50 - 55lb mark. If you use the minimum number of strands, Fastflight strings need to be 'padded out' a bit at the loops so they don't cut into the wood at the nocks if the core wood is lightweight. The centre serving area may need to be double-served so the arrow nocks will grip, OR you simply make a fastflight string as thick as a Dacron string.

I have used only Fastflight type string material for all my bows ever since it became available. I always used it on my all-wood bows and have never had a single instance of damage of any kind in the almost 20 years that it has been around. I have no use for Dacron.

[GrahameA]

Afternoon All.

This is a link to a PDF copy of the old AMO Standards.

http://www.outlab.it/doc/amostd.pdf

If you don't have a copy it would be something that is well worthwhile saving to your Hard Drive.

People playing around with bows will get benefit from reading and understanding it.

Reading the Standard it says that for a string for an AMO Recurve bow the string length is 3" less than the Nock-to-Nock length. It is generally correct for most commercial bows - you will need to fine tune the string.

[morganp]

amo-std
thanks for that, will read