# Spine of wood arrows



## clover leaf (Mar 11, 2005)

I have a question about spine. I have read that wooden arrows are typically spined for a 28" arrow. But what about the other variables? Are they typically spined for a 125 grain head? Is it a matter of trial and error (without a spine tester) if you shoot say 27" or 29" to get the right spine? Is it also a matter of trial and error if you use a lighter head say 110 grain as opposed to a heavier head such as a 190 grain head? How much does string material affect spine? I have heard that if you use fast flight you should use a slightly heavier spine for your set up is that true? If anyone can answer these questions for me I would appreciate it. I have a pretty good idea as to how this all works but I would like some other opinions as I am thinking about going to some type of wood shaft this fall. Thanks


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## rraming (Aug 5, 2006)

The information you have said is correct - 125 grain yes. A HIGH topic of debate around here choosing your spine. Shoot anything from your lbs your drawing to 10-15 lbs over - it is trial and error. Some vendors sell test kits, I never used them I asked some old guy what spine and he knew what I needed. You can ask the old guy too his name is Lamont at The Footed Shaft. I suppose you could call 3 Rivers too.
Increasing you tip weight makes the shaft weaker and vice-versa also using fast flight strings vs B50 would make the shaft weaker ( may involve shortening the shaft by 1/4" - not a whole different spined arrow, not a huge affect) as well as would adding feathers to the back


You'll love em


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## AKRuss (Jan 10, 2003)

Spine is a standard measurement of the amount of flex in a shaft. The old wood arrow, or AMO, spine standard has 26" centers (shaft supported by uprights that are 26" apart) with a 2# weight supported at the center. The actual spine measurement is the deflection or displaced distance measured at the center. The weight determined is simply 26" divided by deflection in inches. So, a 0.500" deflection would give you 26/.5=52#. Although measured at 26" centers, the designated weight is based on what is/was considered a standard arrow length of 28". This is a measurement of "static" spine. The way an arrow actually flys out of a bow is the "dynamic spine". The old rules of thumb are for every additional inch of arrow length or 35 grains of point weight, the arrow is dyanmically despined about 5#. The reverse is also true. As you can see, static spine is simply a standard way of measuring arrow flexibility and not a direct method of determining what spine you should shoot out of your bow. For what it's worth, I find, say, a 50# spine arrow is over spined for a 50# selfbow, about right for a 50# Howard Hill type longbow and way underspined for a 50# centershot recurve. It's just a standard. 

It may be of interest to note that there is a new spine standard that I like to refer to as the synthetic arrow spine that is now used by all manufactureres of synthetic arrows - carbon and aluminum. The new standard is based on 28" centers and 1.98# weight. The equation to determine this new static spine standard is 28"/deflection"=weight. These standards are now maintained by ASTM, who charges money to see them. I paid to see the new spine standard and I think I paid $35 or so.


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## AKRuss (Jan 10, 2003)

I didn't mention that static spine does not take into account point weight. I consider 125 grains to be standard. Howard Hill considered 160 grains standard. Others like more or less. You need to find the correct dynamic spine for your setup and technique. A light weight string certainly speeds things up and may call for an extra 5 or so pounds of spine. It really depends on the bow.


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## clover leaf (Mar 11, 2005)

*Spine*

Russ 
Thanks for the info and to think some guys think Trad is just shooting a stick with a string on it ! 
No really your info was informative and helps me a little more with SPINE. I had what I thought was a good handle on it but had never been exposed to the technical aspect that you explained. I did understand that different styles of bows (sellf bow, longbow, recuvee, compound) while all at the same weight (say 50#) have different ways of launching an arrow and the "spine" may be different for the same "poundage" thanks!


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## GBG (Mar 4, 2007)

Are there specified dimensions or geometry for the upright supports or hanger where the 2# center point load is applied?


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## AKRuss (Jan 10, 2003)

It's interesting to note that spine testers are a relatively recent invention. The early English arrow makers estimated spine by hand. Primitive archers used various amounts of bow canting to make up for lack of spine consistency. 

I don't know of any standard for the uprights. Obviously you want a fairly sharp edge, enough height for weight clearance and precise distance measurement. I have three "factory" made spine testers that I'll try to photograph tonight. One of my testers I've dubbed the "Mother of All Spine Testers", LOL. I made my first two spine testers but gave them away years ago.


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## AKRuss (Jan 10, 2003)

A few pics of spine testers to those who are interested.


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## AKRuss (Jan 10, 2003)

Hmm, just trying to figure out the photo thing, LOL. The above is an Adams spine tester. Below is a Flight-Rite Tester ...


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## AKRuss (Jan 10, 2003)

The "Mother of All Spine Testers" an Easton Pro-Shop tester. Before you get too excited, they don't make these anymore. It came complete with "Master Shafts" to make sure you zero properly.


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## AKRuss (Jan 10, 2003)

A few more pics of the Easton tester ...


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