Folks,

I made a spine tester recently with the caliper tool, similar to the poor folk bow version.

I measure my GT 3555 on it and come up with a .500 spine. So far so good, right?


I just started making woodies and received a dozen or so cedar shafts from a friend. He labelled the spine on each shaft. My measurements are coming up 5-8 lbs less than his.

My question. Will I get different readings from carbon and wood? Is there something I am missing. Could my friends measurement have been off?

Hmmmm.  Don't know that I'm familiar with the home made caliper version spine tester.  However, the standard for spining wood arrows is a 2# weight, with the arrow suspended between posts 26 inches apart.  A while back Easton began using a different set of paramaters, which became generally accepted for carbon arrows.  It's a 1.94# weight with the shaft suspended between posts 28 inches apart.  They do yield different deflection results.  

If you and your buddy are using the same type of spine tester, you should get the same results. If he's using one, and you the other, the results would disagree.  Also, wood can change spine if it's unsealed, and even when it is sealed.  For example, the spine I get on my arrows in mid-summer, when it's generally damper than the dry air inside my house in winter, often varies by 3-5# from the spine in winter.

Of course, the spine on a wood shaft can vary by 3-5# depending on how it's oriented to the weight when on the spining tool.  The grains should be perpendicular to the weight.
In short, lots of things could account for the difference.

Ditto everything Orion said; and with the 'regular' tester you need to 'zero' the tester between shafts.

Thanks guys. I am using a 2# weight. Exactly 2#. The arrow is set on two dowels measured 26" apart. My carbons measure out just as they are labelled. The woods are 11/32" and I zero the tester every measurement with seemingly tight tolerances.

I'll check his tester when I have the chance. Thanks for your time!

Might want to spine more of the GT's on a different (calibrated) tester.  Very rarely do you get one that spines .500....just sayin'.     :D

What should the spine in at. Is has really been around .502 or so.

Ditto what Orion stated - ensure you have the wood grain of your cedar shafts oriented correctly.  If your buddy had them oriented w/grain vertical vs horizontal you will have a difference of up to a few pounds.