For Experimenters - Determining Weak side of Shaft

Discussion in 'PSE TAC 15/15i Crossbow Hunting Forum' started by OkieBowie, Apr 20, 2011.

1. OkieBowieWell-Known Member

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lightbulb Warning: The following is meant for experimenters.

Note: The following in no way is meant to say or even imply "this is how it should be done".
Also: Apology in advance to Physicists if the wrong terms are used. My major was all binary, as in "1s" & "0s".

In another thread I suggested an alternative method to using the traditional (and blessed) method of using a Spine Tester to determine the weak side (vs. strong side) of arrow shaft. The suggestion grew out of reading some information dealing with the issues of Arrow Tuning. Specifically that Spine Testing is static in nature, whereas an arrow upon release undergoes dynamic forces.

Traditional Spine Testing determines the weak side of an arrow shaft based on downward forced (say 5#s) placed near the middle of an arrow shaft with upward (opposing) forces at each end of the shaft. The weak side is then divined by rotating the shaft to find the maximum downward shaft deflection with something like a Dial-Caliper.

The issue is, Spine Testing is using what would be side forces (pointy-end, middle, and knock-end) on an arrow when it is being released. However, for the most part there is very little side forces. The majority of force is the string shoving the arrow shaft forward, trying to overcome the mass of the arrow that is resisting (pushing backwards).

This led to the idea of gradually applying force (granted still static force) to the ends (pointy-end and knock-end) until the arrow shaft, near the middle, bent in any direction. With the arrow shaft side outwardly bowed indicating what would be the weak side of the arrow shaft as it experiences the force of being released.

An initial, quick & dirty testing using a standard bar-clamp to apply end forces was disappointing in that the arrow shafts did not consistently bend towards the same side. But like any such test, things are not ideal, and other things are learned.

Another round of testing was done using a higher-quality (read more expensive) bar-clamp that had flat jaws that stayed 90-degrees to the bar (flat thick rail) and did not deflect side-ways. The use of this 90-degree jaw bar clamp produced consistent (aka repeatable) results as to indicating what may be the weak-side of arrow shafts, as flung.

Further refinement was made by changing the field-point from a very sharp point to a small rounded end. The same was done with the arrow knock which originally was made very pointed.

Additionally, a new method was used to determine the most outwardly bowed arrow shaft side. Which involved, repeating the bending, while rotating the shaft till it always went directly up (180 degrees from the bar clamp's flat rail). I know this sounds time consuming, but it actually goes quickly.

Overall, this new end-to-end force method produced very consistent results that compared favorable too the previous marks that indicated the weak-side. However, here in lies the issue.

The results were utterly different from those done via a home-built (do it yourself) Spine Tester. The results varied from being off by roughly 90 degrees to nearly a full 180 degrees.

gun) I need to state, my results are by no means definitive. There very could well be issues with accurately finding the weak side of an arrow shaft with my home-built spine tester, that would/will be shown out by a Professional model Spine Tester. Anyway...

All of this experimenting and testing has led me to ponder if the only way to really find the weak side of arrow shaft is to find it by firing the arrow and capturing the event with an accurately timed flash photograph (digital image).

If there are any experimenters out there who happen, just happen to have a high-speed camera - Could you try capturing a few TAC-15 arrow shots with the arrow marked to where one could possibly see if the arrow bends to the weak-side as indicated by a traditional Pro Spine Tester? (Thanks in advance.)

In the mean time, I plan (attempt) to see if I can rig up a cheap camera and flash, to be triggered just as the arrow starts to move forward. And hopefully detect the weak-side of several arrows based on captured images. At issue is the aforementioned "cheap camera" which as of yet does not have a remote shutter-release, and then the issue of building a sensor/circuit to trigger the flash as the arrows start forward.

That is all for now...

2. OkieBowieWell-Known Member

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Time to fess up, I goofed.
1) I was marking the strong side, not the weak. Thus the arrow with 180 degrees, was almost spot on (aka I got lucky with that arrow shaft).
2) As for the two with roughly 90 degrees, those turned out to be a combination of three problems: a) A case of not making the marks accurately, b) along with bad estimation on my part as to the difference in positions, and c) issues with using the home-built Spine Tester.

Credit goes to Dorge's Fletching Jig for helping to sort this out. All it took was putting the arrows in the jig with it set to 0-degrees and rotating the arrows to align their Spine Tester made marks with part of the Jig. Then setting the Jig to 180-degrees, and comparing the marks made via bar-clamp to same part on the Jig.

When at first you don't succeed, try again. There was indeed problems with using the home-built spine tester, besides the issue of making accurate marks. Two issues stood out.
1) I could get better results by looking for side of the shaft that most resisted bending (strong-side) from the hanging weights. Not sure why.
2) The alignment (aka positioning to Top Dead Center) of the Dial Gauge to measure the arrow shaft's deflection took more care than I had realized. Along with using a different Tip on the end of the Dial Gauge.

One other thing I noticed was the arrow shafts did not always seem to deflect the same amount when rotated to find the least vs. most amount of arrow shaft deflection. The Dial Gauge itself may be part of the problem in that it takes a slight amount of force to move the needle. Perhaps due to its age and the mechanical workings. Likewise, once an arrow is bent, it does not take much force to slightly change the amount the arrow shaft deflects.

With all that said, it looks like using a bar-clamp to detect the weak-side of arrow does correlate with using a Spine-Tester. (Yeah !)
Based on the two methods, and without having used a Professional Spine-Tester, the Bar-Clamp methods seems to be easier and more accurate in finding the weak-side of an arrow-shaft. Still the proof lies in consistent arrow placement when using different arrows.

In the prior post, I mentioned the real determination on arrow shaft bending would be to image what happens when an arrow is released from a TAC-15. Still working on that.
The El-Cheapo camera I have responds to slowly to an external remote switch to capture an arrow upon release. Even setting the camera to manual everything, which also eliminates focus time, does not help. Thus leading to using an external flash coupled to optic trigger to capture the arrow shaft's dynamics just as it is released.

Cheers, its time for beers...

3. Super 91Well-Known Member

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Fine testing and analysis. Seems your trial and error method is getting your some results, even if they were not what you were thinking to start with.

I am waiting on more TAC shafts to begin testing more myself. I have modified my RAM arrow tester to me more accurate and will be putting that to the test in the next couple of days when I pick up my parts.

Dorge has told me as well as others that a RAM tester or any spine tester will not work on the TAC shafts because the TAC shaft is tapered inside, making the spine different from front to back of the shaft. In other words, the spine for the first 1/4 of the shaft might be 80, then next 1/4 might be 100, then next 1/4 might be 120 and the tail end might be 140 spine. Put that on the spine tester and the machine might show you 140 each time, but only because you have the arrow suspended from 80 to 140. It will flex as much as the weakest spine, I would think.

It will still work to a certain degree, but not with the perfection you might get from testing a standard shaft. The bar clamp tester is a superb idea. But as you have mentioned, a high speed camera would tell all.

We may have to stand back and design a new type of spine tester to accommodate these new shafts with multiple spines. I think you are on the right track and I appreciate the work you are doing.

4. OkieBowieWell-Known Member

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Does fit with what I have seen with the TAC shafts not bending the most in the center of the shaft, but closer to one end. When I get back home, I will have to see if I can measure the bending point with respect to front to back.

You do realize this (flex point) may add yet another variable to getting a group of consistent arrows...

5. Super 91Well-Known Member

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Absolutely....

6. Buzzard BaitWell-Known Member

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Super 91/OkieBowie, I've been following this thread and have what may be a silly question or it might be a question that has no good answer.

From your discussion it appears the Tac 15 arrows have multiple spines due to the way they are constructed (tapered thin at each end, thicker in in the middle, i.e. a sort of reverse coke bottle shape). This shape (or taper) evidently makes the spine different (or variable) from front to back.

If you look at the end of the arrow you have a circle of 360 degrees. Say 0 degrees is up and the spine of the front section is along this angle. My question is......will the spine of each section of the arrow be located at the same angle along the length of the shaft? I.E. could the front section be at 0 degrees, the thicker middle section be at some other angle, say 60 degrees from the 0 degree spine of the front section and then the rear section be at some other angle, say 130 degrees from the 0 degree spine of the front section?

If there is three or four different spines along the length of the shaft that are not in line with each other, could we ever expect to attain the same point of impact with a group (say a dozen) arrows?

I may be out in left field with this question!!!!!!!!!

7. jon.henry755Well-Known Member

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Dec 16, 2010
Hi Okiebowie,
If nothing else I have to hand it to you for your innovative thinking and your ability to construct homemade ways of doing different types of testing. You are by your own descriptions a true tinker which is what makes many of us engineering types similar. We believe that by closely examining almost anything, you can determine what makes it tick and then you can come up with a way to reconstruct it to perform better.

That said, today's Spine Testers are not built to identify the weak side of an arrow shaft. They are designed to first measure an arrows spine, then measure total spine deflection (which is the total shaft flexation from the shafts stiffest point through the softest point), lastly, they allow a person to accurately mark the exact stiff side or weak side of the arrows spine.

In relation to the newest generation of tapered arrow shafts, that is where are industry is definitely heading, but we also need to remember how and why an arrow goes through a deflection timing cycle. This is not static compression, but rather dynamic compression as the arrow is launched from its string or cable. I like the example of placing a 100 pound bowstring on one end and a bowling ball on the other end of the arrow. Where is the arrow shaft going to flex the most. Well, on a uniform arrow shaft, that will always be in the shafts exact center, but on a tapered shaft where different thicknesses are involved, it either moves the flex point slightly forward or slightly backward of exact center. It does not change where the stiff point or weak side of the shaft is located around an arrows circumference and we don't care so much where the stiff or weak side is along the arrows length, since we are matching each arrows deflection cycle close to its center since that's where the timing cycle that creates an archers paradox takes place.

More than anything else in the archery industry every manufacturer understands the need for greater accuracy through more consistency. They are not in the business of creating and manufacturing arrows that can not be matched in Spine, Deflection and Weight. These three elements are the corner posts of accuracy regardless if you are talking about arrows, spears, darts or anything else that shoots.

Remember that Easton Archery had 5 major manufacturing plants around the world and used a very expensive Spine Testing Meter in each plant to testing and sorting there arrow shafts for many years. They had an engineer that was assigned to install and calibrate these testers and maintain a very high standard of accuracy at each of there facilities. Manufactures don't make arrow shafts blindly. If they're making them, they have the tools to test them to insure they're getting the results they want.

They are not in the business of providing us with custom matched shafts other than to insure the Spine of the arrow is in the correct shaft range they are advertising, such as a .250 spine or a .350 spine. to get beyond that, it becomes our headache and the spine deflection meter is the only tool we have that is capable of performing the job to an acceptable degree. I repeat, an acceptable degree, since even the RAM Carbon Spine Testers require some minor modifications before they will operate smoothly. The meter head in the old Easton Spine Testers had much better bearings and sold for over \$800. for just the head. The complete tester sold for over \$1200. It's hard to compare that with a whole Spine Tester like the RAM that sells for under \$300. As the saying goes, "you get what you pay for". The RAM can easily be improved, but I'll leave that issue to Super 91, since he's already completed those mod's and can provide more detail if anyone is interested in the details.

For the average TAC15 shooter, if you did nothing more than have your Spine Tested to mark the stiff side of your spines and then aligned your nocks so that the stiff sides were all in the same alignment to your nocks, you would improve your accuracy from arrow to arrow by a huge margin. If you then worked with a grain scale to match the arrow weights to with 1/10th of a grain (+ or - .3 grains), you would increase accuracy by 80 to 90 per cent.

We already know that within a year from now the technology used to custom fletch and build arrows will change once again. There are new vanes and new bonding methods under development that will likely have a major change on performance and the way we do things today. I'm not here to steal anybody's thunder or talk about the latest innovations, I'm just stating that the information provided in these forums is based upon the latest technology and information that's available to most of us today.

Jon

8. OkieBowieWell-Known Member

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I get where you are going, but from the testing I have done so far, I believe the spine will be at the same angle down the shaft. What I think is at issue is finding the best (being easy, accurate, and repeatable) method of during the shaft's weakest (or strongest) spine side (or angle position).

Sorry to report, but I have not had the time to play with capturing an arrow just as it is shoved forward by the string to see if it bends on the same side as indicated from spine testing.