Arrow Spine

[riarcher]

"[iShoots with growth rings instead of a grain that runs through it would offer equal resistance to bending from any point on the circle,  Just like fiberglass, aluminum and carbon shafts.
][/i]"

I'm not sure how true that is.
I've tried a few things and found that one side seems to always be at least a bit stiffer.
Maybe it's the way it grows towards the sun, way the wind blows, cold side?
Don't honestly know why, but from experience, there is usually one stiffer side.

Then again, maybe I'm splitting hairs and it don't matter as much as I pay attention to it? 

[Pat B]

I have also found that there is always a stiffer side with shoot and cane shafts. Generally with cane it is on the sides where the shoots come out of the nodes.

[zenmonkeyman]

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...

 

Garett

[Steve Cover]

I'm not sure how true that is.
I've tried a few things and found that one side seems to always be at least a bit stiffer.
Maybe it's the way it grows towards the sun, way the wind blows, cold side?
Don't honestly know why, but from experience, there is usually one stiffer side.
Then again, maybe I'm splitting hairs and it don't matter as much as I pay attention to it? 

Since I've never made an arrow out of a shoot.  I have no way of knowing...  My comment was made on an assumption of perfect symmetry of the growth rings.....

If shoots also have a stiffness orientation, I wouldn't know how to visually identify it without trying to bend it in several orientations.....

Quite interesting information.

Thanks,

Steve

[Steve Cover]

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...
Garett

No such thing as a dumb question... If your wondering about something you need to ask.

As far as Archer's Paradox goes, many years ago when I was taught to make arrows out of cedar shafts, it was explained to me that what was desired was finding the orientation with the least willingness to bend and assemble my arrows with the stiffest orientation 90 degrees to the bow.

Also, for better consistency I needed to match my shafts by the amount of bend during a spline test.

There is a chart that lists what weight bow a certain spline number relates to.

Since traditional Spline testing is done with supports set 26" apart and the weight is 2#....  A person should be able to match the spline to what bow weight he is using as long as he is using the standard technique.

This however, is based on a 28" shaft....  A shorter arrow splined to the same numbers as a 28" shaft will actually be appropriate for a heavier bow.....  Shorter arrows have a different bending moment than longer ones.

The reciprocal is also true.  A longer shaft with the same spline numbers, will be less stiff overall due to its longer bending moment.  (Longer shaft is easier to bend because it allows force to use more leverage)

I believe that Archer addressed this in a recent post.  I referr you to him for better qualified details.

It was also taught to me that the arrow fletch/ arrow head weight should fit a certain formula so the Archers Paradox vibration node points were as close to the same length from each end...

Arrow Spline, (or Spine as the current archery world calls it), is complicated by the fact that different bows of the same weight, due to grip width, will rest the arrow at different distances from the centerline of the bow.

Since the bowstring applies its force to the centerline of the bow, the farther the center of gravity of the arrow is from that centerline, the larger the side force on the arrow. 

(Requiring a stiffer arrow to match the same amount of Archer's Paradox bending as from a less stiff arrow from a narrow handled bow of the same draw weight)

An arrow that shoots well from one bow may not be the right stiffness for another of the same draw weight.

If you are as picky as me, you may want to do some experimenting.  However, you would likely have to shoot from a fixed shooting machine as relative long distances to actually detect the difference...

One other quick note:  The traditional spline test as I have described above dates back to the middle ages.  However, there are other spine testing configurations available to the modern archer.

Supporting one end of a shaft and hanging a weight on the other end, and attaching a pointer that points to a scale on a card is another method that is accurate..... 




Traditional Spline Testing Jig.



Spline Chart





There are always several avenues to the same destination.

Hope this helps,

Steve

[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. 

[riarcher]

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...

 

Garett

Errr,,, I'm getting confused! 
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. 

[Steve Cover]

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

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

[artcher1]

Really hard to get involved in these mind benders anymore Pat because of the meds I take. But for the most part you guys have it right, the stiff side goes against the arrow pass. That's if the shaft has a stiff side. You can take your time, using a spine tester, and achieve even deflection all the around the shaft on shoot shafts. But still, you should get the straightest/cleanest side against the bow and the side with the any undulations down on the shelf/hand.

But if you're dealing with inconsistent deflections, look to have the stiffest side of the shaft against the bow and also the stiffest side down that sets on the hand/shelf also. Sometimes this is not possible because of shaft's oriention for that right/left handed person. But take and do a 180 and it orients perfect for the opposite-handed person.  ART

[Pat B]

Thanks for chiming in Art. Sorry to hear you are not doing well. Take care.