Spine vs. spine

[Don Stokes]

Some people claim that spine is spine, regardless of the arrow material. Others say that different materials (wood, fiberglass, aluminum, carbon) have different frequencies of vibration, so spine (measured as deflection on a standard spine tester) is different for different materials, all else being equal, to get the same results.

Has anyone actually tested either theory? I haven't, but it would surely be nice to be able to say, "OK, if you know that 65-70# works for wood, then XXX will work for aluminum, and YYY for carbon, because they all spine the same." Or not, as the case may be.

Has anyone put together a chart that shows relative equivalence of the different materials under controlled conditions, i.e. by a study done by scientific methodology? I know there are a lot of opinions out there, but has anyone actually done the test work in such a way that the results can be shared, and pass "peer review" requirements?

Just curious,

Don

[Jeff Roberts]

Don, thru my experience I have to be dead on with wood and aluminum for the particular bow I am shooting but I can shoot my carbons out of a wider range of bow weights. By wider I mean only 15 lbs. of draw weight. I shoot 65lb bows but can shoot 60 thru 75 lb bows with the same arrow. Any more than that I have to chenge point weight or drop down in spine. To be honest I never tried that method with wood or aluminum. I am sure someone will have that info but I'm not a tinkerer and spend my free time hunting.It would be interesting to see something worked up on that.

[James Wrenn]

Well I have never done any research on the subject for my peers or anyone else.I can however pick any shaft that spines the same out of any material and have it shoot just fine with only minor changes to correct for shaft diameters.Of course there will be slight differences between a fat wood and a skinny carbon that effects centershot of the bow.If you have room to adjust for centershot changing is very simple.jmo

[Earl E. Nov...mber]

Kelly's testing of Aluminum shafts, pretty much flew in the face of Easton's chart for stick bows and most agree it is much more accurate.

 http://www.arrowsbykelly.com/Spine_Charts.html

[SHOOTO8S]

Not sure dynamic spine can be tested with scientific methodology. However I have found to be true time and again shaft material weight effects dynamic spine . For instance a carbon shaft that weighs 6.1 GPI will show a stiffer dynamic spine than a wood or alum shaft that weighs 11 GPI, even though both have a static spine of .500. Heavier shafts show more paradox, simply because it takes more energy to make them move.

[James Wrenn]

I agree with the weight change thing for sure.I would not buy the same spine in cedar shafting as I would in a heavier material like laminated birch or expect a shaft to shoot the same after sticking in a weight tube.Like you say the heavier material absorbs more energy and needs to spine more.

[Don Stokes]

Yes, the weight issue does complicate the comparisons. It should be easy to find wood and aluminum that would compare in weight, but I don't know about carbon. I haven't shot anything but wood since 1987.

Rod, if you load the point of that 6.1 gpi carbon to get it to the neighborhood of 11, will it then shoot the same as the same deflection aluminum?

James, your experience with changing between materials with minor adjustments is the sort of thing I'm wondering about. Seems like it would be possible to make a chart that would show which shafts shoot the same when the variables are accounted for, like arrow weight and adjusting for diameter effect on centershot.

Maybe a Master's Thesis for some enterprising graduate student...

[Night Wing]

I don't use the aluminum chart done by Kelly since the recommended sizes for aluminum don't work for me, too weak in spine. I prefer the aluminum chart used by Brackenbury.

 http://www.brackenburybows.com/Tuning%20Tips.htm

[SHOOTO8S]

Originally posted by Don Stokes:


Rod, if you load the point of that 6.1 gpi carbon to get it to the neighborhood of 11, will it then shoot the same as the same deflection aluminum?

Not really...if the difference of 6.1GPI vs 11GPI is added to the point only..the shaft will show weaker dynamic spine, due to all the extra weigh being at the front of the shaft, which will move last and require more enery to move, but the rest of the shaft will deflect more due to the resistance of the front with added weight.

[Bear Heart]

Don't overlook the cut of a bow.  I just found this out the hard way.  Past center means a stiffer arrow.  Before center means a slightly weaker shaft will be needed.  That is why you can't have an exact answer.  Only ballpark charts that will get you on your way.

[O.L. Adcock]

Good post Don and the simple answer is, no, a "chart" could not be made due to all the variables involved. A biggy that no one has mentioned is diameter differences. I have to laugh when folks ask for recommendations for this bow or that when you and I could have the exact same draw length and a bow perfectly tuned for you would not shoot for me and vice versa. All the charts are "guidelines" to get in the ball park from there tuning is still required.....O.L.

[SHOOTO8S]

Good point O.L.....I spent a lot of time and misery trying to figure out why I couldn't shoot the same spine range as others...and of course the answer was there's way too many factors that effect needed spine.

[LBR]

Glad this one came up!  Several years ago I tried some ash shafting, and needed a heavier spine than I shot in POC.  Never was sure if it was just me or what.

Chad