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Arrow Spine
stringstretcher:
Having studied spine and it values for a long long time, one of the easiest ways, and best to get you started in the right direction for a specific spine you can use these formulas. They work, believe me
If you take the number 26 and divide it by the lbs you are shooting it will give you a starteing deflection
IE" 26 divided by 52lbs would be a .500 deflection. Now all this is based on a 28" arrow.
If you take the spine as you know it for the old AMO method of measureing and divide it into 26 you will get the given poundage for that spine
IE" 26 divided by .500 equals 52 lbs.
Now if you have a deflection form a modern spine chart, ie measured with the 28" and a 1.94 lb weight, if you take that spine value, and take 31.5 and divide it by that deflection, it will give you the amo poundage for that arrow.
And one last step. If you take a modern deflection number and take .825 and multiply it by that deflection, you will have amo deflection
Hope this helps
Pat B:
With modern spine calculations you have to consider that you will be using a 125gr point(like Steve indicated) Points over or under that value will make a difference. I'm not sure of those values.
I wish Art Butner(artcher1) would chine in.
My brain has a hard time figuring these things out. I am repeating what I was taught, not figured myself. ZMM, I try not to over think this kind of stuff. It really fogs my brain. If it works, I use it. ;D
riarcher:
--- Quote from: zenmonkeyman on February 11, 2010, 03:02:24 am ---I'm probably overthinking this, but is the stiff side the side that doesn't want to stretch, or the side that doesn't want to compress? Do you want the arrow to be at its MOST willing to bend around the bow, or at its LEAST? Hope I'm making sense, and I hope somebody will answer a probably-dumb question...
:D
Garett
--- End quote ---
Errr,,, I'm getting confused! ::) ;D
Basicly,, the stiffest side into the window of the bow.
Amount of stiffnes is determined by trial. Charts are a rough starting point. (.....I think. :-[)
Pat B:
Modern spine calculations are set for dowel shafting and other modern shafting(ie, alum, carbon). With hardwood shoots and cane, for me at least, it is a bit of a guessing game. If they shoot well, that's all that matters to me. The ones that are iffy become flu flus for squirrels. I can't hit them with good arrows so the not so good ones work just as well. ;D
Steve Cover:
--- Quote from: stringstretcher on February 11, 2010, 08:46:37 am ---Having studied spine and it values for a long long time, one of the easiest ways, and best to get you started in the right direction for a specific spine you can use these formulas. They work, believe me
If you take the number 26 and divide it by the lbs you are shooting it will give you a starteing deflection
IE" 26 divided by 52lbs would be a .500 deflection. Now all this is based on a 28" arrow.
If you take the spine as you know it for the old AMO method of measureing and divide it into 26 you will get the given poundage for that spine
IE" 26 divided by .500 equals 52 lbs.
Now if you have a deflection form a modern spine chart, ie measured with the 28" and a 1.94 lb weight, if you take that spine value, and take 31.5 and divide it by that deflection, it will give you the amo poundage for that arrow.
And one last step. If you take a modern deflection number and take .825 and multiply it by that deflection, you will have amo deflection
Hope this helps
--- End quote ---
Thanks.
It's been a while since I worked with the formula itself. I've just been referring to the deflection chart on my tester for years, not really caring how it was calculated as long as it worked for me.
That was useful infomation.
Steve
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