Spine question

[snuffbox]

Now I understand how aluminium arrows can have a soft and hard side(seam) but how does this work with carbon arrows.
I thought they were constructed so there wouldn't be spine as such,could someone out there educate me please.

[diesel]

Alums have less than carbons do. I have been looking in to this and do you want to talk about a can of worms.
There is a stiff side and a soft side and they are located 90 degrees apart .

Here are a couple links you can read they are talking about golf club shafts but it about the same thing.

http://www.tutelman.com/golf/shafts/allAboutSpines.php

http://www.tutelman.com/golf/shafts/FLO ... outofplane

If you want more I can do that too.

[Boo]

To make things more complex often carbons have two spines, one much more promenent than the other.
I've just started to look at the BEA Zombie Slayers. They are 25% stiffer than the Executioners that are a 300 spine. The spine on the Zombies are almost not detectable. After talking to BEA I believe there is no reason to locate the spine on the Zombie shafts.
I believe that the moral to that is that the more over spined your shafts are for the application the less important locating the spine is. I would love to run a test on a Vixen but I have no time. But this would explain why the Vixens are so accurate and why it is harder to make the heavy bows shoot well and why the Matrix bows are so accurate with their short arras (shortening shafts dramatically increases spine).

[Big John]

As well, take that same example with the Zombie Slayers at 20"in. and try to find the spine at 18"in.!!! Definitely not necessary to locate on those. I am all for finding spine and such when needed or if needed, but, if you are shooting bullzeyes at forty and fifty yds. everytime with a rest, without spine located, how much more bullzeyes can you get with it located? 100 percent is 100 percent. These stiffer spined arrows are ultimately bullzeye magnets without spine locating. Period!

Big John

[Boo]

Be careful if you do look for a spine on a Zombie shaft. They do not bend easily and I know some young guy (not chinese food ) that broke one!

[Bullzeye]

Ok , I know if I do a search I could find the answer, but I am lazy tonight, what is done to find the spine on an arrow ?

[Big John]

As well, I would highly recommend the Zombies to any Bow shooting 325 or better any day!!! Not for any reason other than they perform as needed, exactly as needed from those bows. I will post pics of them from Exomag 200 as well Matrix 355 on Tuesday. Again from yardages out to 50 and 60. From my elbow rest only again. And I wont bother with spine at all! I did not bother with spine last times either. They were still Bullzeye everytime. Spine need only be located on weaker arrows. And if your using a high off set and helical, spine wont get you much more accurate than your getting already.

Big John

[newbie]

Be careful if you do look for a spine on a Zombie shaft. They do not bend easily and I know some young guy (not chinese food ) that broke one!

I wonder whom that was Don? Us young guys don't know our own strength

[diesel]

There are a few different ways .
You can use a RAM spine tester. The shaft will rest in a V of some kind @ each end. In the middle of the shaft you hang a weight and you have a dial indicator that will measure how much the shaft flexes as you roll the shaft.When you get to the place where the shaft has the least amount of flex that is the spine.

You can also do a bearing test to find the spine. Here is a video where they are finding the spine on gulf clubs you can do the same thing with arrow shafts.

http://www.youtube.com/watch?v=I3-x6YjhrTo

[Boo]

Larry how have you dealt with secondary spine? Have you ignored the minor spine? Are you putting your cock feather on the main spine?

[snuffbox]

Thanks for your input on this,over here we shoot a max arrow speed of 300 fops and bow weight is usually the 150 vixen although some favour the GTFlex ten point.
A friend of mine who in his day was a top national and international target crossbower sent me this,which pretty much sums up a lot of what's been said.

Regarding your questions:-

Spine checking arrows?

I used to when I was using alloy shaft material. But even then, I always group-matched my bolts by shooting them. In my experience it doesn’t matter how much trouble you take in assembling arrows – checking the spine, the weight of the components and so on - the only way to select a set of arrows for competition use is to shoot and group match them.

With modern crossbow bolt shaft material, the carbon construction is designed to give a more uniform spine value around the circumference of the shaft. So spine variation is less of a factor when deciding where to position the cock vane. So I don’t worry about it when I assemble my bolts.

Gold Tip – like all the other arrow manufactures – fletch their arrows by machine. I’ve never seen any indication in their literature that arrow spine is taken into account during the assembly process. I don’t think that it would be practical to do that anyway.

After I’ve assembled a new set of bolts I group match them down at my archery club. I usually do this early morning or late evening so that conditions are at their calmest. Shooting from, say, 50 yards and using my IdleBack shooting chair (see photo) I can easily work out which bolts will group best together. I also check to see if by indexing the cock vane I can “dial” an errant bolt back into the main group. This sometimes used to work with thinner-walled target spec alloy shafts, but less so with hunting spec (thicker-walled) alloys or all-carbon shafts.

But at the end of the day Paul, we only need 1 arrow most of the time (Ha!) at NFAS shoots. So selecting two or three well matched arrows shouldn’t be too difficult to do.

Several crossbow arrow manufacturers are now publishing ballistics data on their websites. I guess that you’ve already seen this info' on websites such as ‘Gold Tip’ and ‘Ten Point’? If not then it’s well worth a look.

All the best, Chris

[Masboy]

No matter how close I try to make my arrows all the same I find the only way to get arrows with about the same exact poi is to tinker with them then shoot an sort them . I play with one arrow at a time an try to know it well . works for me

[diesel]

Don
I have been talking with Jerry @ SSA and with his ,Grims and Dropzones from CBN I have been FLO testing the shafts. We feel this will be a much better way to test an than know where to install the Cock feather . I'm putting the cock feather 180 degrees from the strong FLO plane that puts my NBP ( natural bending plane ) @ 90 degrees .
The natural bending plane is the weakest plane, that is where it bends the easiest. The neutral bending planes, of which there are 2, the weak and the stiff( which are at 90 degrees to each )


• Why is FLO[1] important? Because it is the most simple and direct measure of the real direction of the spine and NBP.
• Why does a "spiny" shaft wobble when plucked? Because the spring forces due to bending the shaft are not in the same direction as the bend itself.
This article explores the above questions, with illustrations, analysis, and even some math -- sorry 'bout that to those of you who are trigonometriphobes.

Here are the topics we'll cover:

Some basics of how a shaft's stiffness varies with direction.
Don Johnson's "shaft art", which shows exact trajectories of shaft wobble.
A few similar phenomena: Lissajous patterns on oscilloscopes, and the Y-pendulum -- an experiment you can do.
The equations of shaft art -- they're remarkably simple and fit easily on a spreadsheet.
Why shafts wobble in the first place, and how much they wobble.

The Basics
Let's start with a functional description of a golf shaft in engineers' terms, not golfers' nor clubmakers' terms.

A shaft is a spring. This is very basic, but it has a number of implication that are important to understanding FLO:

Since the shaft is a spring, it responds to being deformed by exerting a "restoring force". If you deflect a shaft with your finger, the shaft will exert a force on your finger. The force is called a "restoring force" because it is exerted in a direction to bring the shaft back to straight. (Well, almost. We'll see why "almost" toward the end of this article.)
That restoring force is proportional to (a) the amount of deflection, and (b) the stiffness of the shaft. This is true of all springs. Mathematically, engineers talk about it as F=-Kx, where F is the force, x is the amount of deflection, the minus sign is because the force is in the opposite direction from the deflection, and K is the "spring constant" of the spring; in the case of a golf shaft, K is a numerical representation of the stiffness. Yes, we all know that frequency is also a numerical representation of stiffness. K is a little different; instead of cpm, it is expressed in pounds per inch of deflection (or newtons per centimeter, or other units of "force per distance").

The shaft is not only a spring; more specifically, it is a flexible beam. Note that I didn't say, "Perfectly symmetrical flexible beam." We're talking about spine and FLO here, so we are exploring what happens when the cross-section of the beam is not symmetrical. That leads us to a few more facts that engineers know about flexible beams, even asymmetrical beams:

If you deflect the shaft and measure the spring constant (the stiffness), then deflect it in exactly the opposite direction (that is, exactly 180º away), you will get the same spring constant. It is equally stiff in both directions.
If the cross-section of the beam is not perfectly symmetrical, then the beam may have a strong plane (the direction of highest spring constant) and a weak plane (the direction of lowest spring constant). Clubmakers refer to the strong plane as the spine and the weak plane as the Natural Bending Position (NBP) -- or at least they should if they are using the right measuring instruments. Repeating that as a table, for clarity:
Strong plane Weak plane
Direction of
highest spring constant Direction of
lowest spring constant
Spine NBP

The strong plane and the weak plane are 90º apart.
Between the strong plane and the weak plane, the spring constant varies as an ellipse, as the diagram shows.
If the shaft were perfectly symmetrical, then the ellipse would be a circle, and the spring constant would be the same in every direction. That would be a shaft with no spine.

These rules are true no matter how asymmetrical the shaft. You could weld a steel rod to one side of the shaft, and the rules would still be true. I'm not going to explain here why this should be. But it has been well known to those studying structures for a long time. I have even found a mathematical proof of it in Timoshenko's classical mechanics book[2], which was written in 1930.

Before we go any further, let's state some assumptions underlying the rest of the work:

Whatever asymmetrical stiffness the shaft has, it is the same (including its orientation) for the length of the shaft. (It turns out that this isn't a major restriction, but it's hard to show that fact so I won't bother.)
The shaft, when flexed either for "shaft art" or by a golf swing, remains a linear spring. Almost every spring material and spring design has some level of deflection where F=-Kx fails. We assume that this doesn't happen to our shaft in normal operation.


One final "basic". Let's look at how a shaft oscillates when there is a spine -- how it gets from a planar up-down vibration to an out-of-plane oval. Here is a video example, using a shaft with a really substantial spine.

[Mister B]

For a hunter like me who refuses to take a shot over twenty yards,( my choice is 15 or less and I have taken more deer than my age, only one of which was over 20 yards) I think you are trying to polish a diamond with wax paper. Spine doesn't really matter if your bow can put the arrow within a silver dollar spot at these hunting distances. Granted, occasionally you get an arrow that refuses to cooperate, but I've had duds in bullets too. Practice. If it hits, use it, if it don't chunk it. Just my honest opinion. I went to a lot of trouble making a spine machine with all the gages and weights, but push come to shove, my time is better spent practicing. Sorry if I am peeing in anybody's snow.

[Boo]

For a hunter like me who refuses to take a shot over twenty yards,( my choice is 15 or less and I have taken more deer than my age, only one of which was over 20 yards) I think you are trying to polish a diamond with wax paper. Spine doesn't really matter if your bow can put the arrow within a silver dollar spot at these hunting distances. Granted, occasionally you get an arrow that refuses to cooperate, but I've had duds in bullets too. Practice. If it hits, use it, if it don't chunk it. Just my honest opinion. I went to a lot of trouble making a spine machine with all the gages and weights, but push come to shove, my time is better spent practicing. Sorry if I am peeing in anybody's snow.

No question. The other side of the coin is that some like to whack targets like it owes them money so locating a spine is for them.
Normally I just assemble my arras and shoot them. Any "fliers" found still get used because those "fliers" still kill at hunting distances. I aim for the lungs and that's a big target!