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.
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...