ILF, and probably general bow/limb issues

[JohnnyBa]

I swear, I am just not even getting why numbers are even put on bows and limbs. My frustration is coming from ILF, but maybe all TD bows have this issue if limbs are interchangeable. My example is this, I have a 15, 17, and 19” ILF riser, and they are those exact measurements. The fun stops there. I have a TBow Santori knockoff and it is advertised as a 62”, as in, the ad states this is a 62” retake down recurve bow and I ordered with 45# limbs and an extra set of 50# limbs, same TBow brand. I did not even know there were different length limbs at this time and I “assume” these are mediums. Anyway, there is nothing about this bow that relates to the # 62. The bow, unstrung is about 57 inches, laid on a tape measure tip to tip. The bow, strung, is about 58 inches with an 8 inch BH. The string is shorter than that. There is no 62. It only gets worse with aftermarket stuff as I ordered long Sanlida x8’s that said 64 on a 21 inche riser, they should have been 62 on a 19 in riser but numbers were as screwy as before. What is up with that and is there even a better way to get a bow length measurement?

[McDave]

Bow length is measured along the limbs, including the recurved part of the limbs.  Take a piece of string, or better, one of the cloth measuring tapes they use in sewing for measuring around a person's waist, and place it on one limb tip and measure along the limb, including the recurve, until you get to the other end.  That is the bow length.  The number they give you is only approximate.  I doubt there are many 62” bows that are exactly 62”, which is why it is helpful to know the length of a string that actually fits.

[JohnnyBa]

Does measuring any bow in this manner give you the number in which to determine string length? How does one “Know” string length if you are building your own bow or buy one that doesn’t have a string? For that matter, picking nits here, how do we know the string is right when we buy a used bow?

Bow length is measured along the limbs, including the recurved part of the limbs.  Take a piece of string, or better, one of the cloth measuring tapes they use in sewing for measuring around a person's waist, and place it on one limb tip and measure along the limb, including the recurve, until you get to the other end.  That is the bow length.  The number they give you is only approximate.  I doubt there are many 62” bows that are exactly 62”, which is why it is helpful to know the length of a string that actually fits.

[McDave]

If you give a string maker the actual length of the bow, measured as I wrote, or if the string maker is already familiar with the make and model of the bow, he can make you a string that will fit.  You also have to know the brace height of the bow, because the higher the brace height, the shorter the string should be.  A rule of thumb would be to use a string that is 3” shorter than the length of the bow for a longbow, and 4” shorter than the length of the bow for a recurve.

That said, I have made a lot of strings (for someone who is not a professional string maker) and I have a nail on my wall that is full of orphan strings that came out a little too long or a little too short.  I keep hoping that I’ll find a use for some of them someday.

[JohnnyBa]

Thanks McDave! I think I see the light, finally, and took that light and done me some measuring. Things make sense now that I DO have what I bought and now know how to keep it that way. One thing I know now, if my obsession doesn’t wane soon, I am going to have to learn me some strang weaving, 

[Kirkll]

I’m going to throw a bit of a twist in this…

Every set of limbs you purchase will have a different shape and limb design. The old school thoughts that 3” shorter on a long bow, and 4” on a recurve does not really apply to most AMO length bows today……But 3” is a good starting point on both long bows and recurves if you cannot get a recommended brace height from the limb manufacturer.

All of my bows measure at very close to AMO length such as Dave described above…. But…. The actual string length on my limb designs are longer than most. 2.25” to 2.75” shorter than length is very typical for both long bow and RC limbs I build….. Going with a shorter string and raising the brace height over 8” is shooting yourself in the foot. Your over all performance will suffer considerably.

I try and stay with a 7-7.5” brace height on allmy bows,  and have designed the preload on the limb accordingly. but some long bows shoot better at lower 6.75” brace….

So the bottom line is…. Every set of limbs you string up will have a sweet spot for brace ht and provide the best string tension. The ILF system allows you to adjust that string tension, tiller,  and preload with the limb bolts……but …you will need to try different string lengths to find optimum performance.

Hope this helps a bit…. Kirk.

[M60gunner]

Measure like McDave said. Recently I bought a set of limbs, ordered a string for a 64” Bear TD. The new string gave me a brace height of 9”. An inch too much. Reordered using the same measure technique as McDave described. It’ not about an inch shorter than the AMO recommendation. I now measure, not just my ILF combinations but any bow.

[Kirkll]

I’ve seen a lot of the old Ben Pearson, and Bear bows that were sporting way too short of string with 8-9” brace using the 4” shorter system. Even those old bows like a shorter brace height than most guys shoot them….

It’s definitely worth measuring the string before ordering the next one, and once you find that sweet spot, write down that measurement.    Kirk