Some guys will shoot each arrow and turn the nock until they all year the same
In building ng fishing rods the spine should be on the top of the rod to produce the most power out of the rod.
I'm not really sure where spine should be on an arrow shaft. Would like to know the correct answer.
When I find "flyer" shafts based on shooting results, I've never seen any visual indication (like wall thickness variation or any other clues) as to why the stiffness varies around the circumference of the shaft....if that's what you're asking. Some brands seem to be more prone to variation than others. It is an absolute certainty though, that all carbon fiber tubing has manufacturing variations that cause the stiffness (what we call "spine") to vary along the length of the tubing, and around the circumference of the tubing.
You can make the process as basic or as complex as you want, depending on how finicky you want to be. I should probably be more careful, but tend to use to a simpler system, in which I fletch my shafts without considering radial stiffness variation. Then if I notice a "flyer" while shooting, I index my nocks 120 degrees to see if the shaft will fly to the point of aim. If no luck on the first try, the next move is rotating the nock another 120 degrees. Hopefully that works because the next 120-degree move puts the shaft back to the point of beginning. OTOH, if your rest set-up allows it, you can make smaller indexing moves if no worries about vane clearance.
The process cited by Ermine above, in which a spine tester is used prior to fletching shafts, in order to locate the radial position on each shaft with maximum stiffness, is a far superior method, if you want to go that far.
LINK's Link
Cam lean also can affect the direction of the arrow's flex or movement. If nock travel from the cam(s) design is zero, but the cam's lean is significant, then the spine should be at either 3 or 9 o'clock.
If you have both cam lean and non-level nock trave from the cam(s) design, then the spine needs to be at some angle that most negates that induces arrow flex or movement. It is therefore best to shoot through paper with a bare shaft, rather than using a mechanical spine tester, to determine the best nock position.
I stopped shooting Gold Tips many years ago because the quality control was so poor. The last set of shafts I got from them had spine ratings all over the place.
Screw a head on and test for spin. The vast majority of times it will shoot just fine like that. I fletch all my vanes the same color, so in the very rare circumstance where I get a bit of a flyer, I just rotate the nock to the next vane up spot and shoot again. I can usually get it tuned back into the group by doing this. If not, and this pretty much never happens, that arrow gets relegated to practice only (field point) status.
If your broadheads are off by inches, you have other issues and I don't think indexing is gonna help much. It could be a bow tune issue, but it could also likely be the indian and not the bow. Grip torque and trigger punching will kill broadhead flight.
If you please, give us all your set up specs and lets start there...
The question is, with arrow shaft being such a short, stiff length of carbon, is there a way to determine the stiffest direction of a shaft without owning special equipment? Ideally, is there a way to determine it with an already fully built arrow? Conversely, would a well equipped bow shop have the tools to measure the stiffest blank shaft plane and fletch etc accordingly?
Adding to the challenge, based on comments above looks like with a bow where the nock is moving vertically during the shot (e.g. assume Matthew singlecam) or laterally due to cam lean, you're going to have to tweak the nock to get the spine direction sweet spot for the bow regardless.
For guys who have measured this, which hunting grade arrows have the least variation in spine stiffness for a listed spine? Has anyone attempted to measure it cross-sectionally as well as linearly.
I am starting to realize why target guys will drop a thou on a batch of really highgrade arrows.
You're absolute right about finding the stiff side of a fishing rod. It's easy. FYI freshwater rods should be built with the stiff side up and down. Heavy duty saltwater rods should be built with the weak side up or else a big tuna will twist the rod out of your hand. More accurately, if you're wearing a harness to fight a big tuna it can take you off your feet.
Finding the stiff side of arrow shafts isn't too hard. I lay the arrow on something padded (but not too padded) like a soft mouse pad or a paperback book. Lift up one end of the arrow while pushing down in the middle and try to spin it. It will try to resist spinning when you are pushing on the soft side. When you're pushing on the stiff side it will try to spin because its unstable there.
If you can shoot bullet holes in paper with a bare shaft, there is no need to paper tune with fletching. Some can shoot bullet holes in paper with a bare shaft at 20 yards. Such a bow is tuned and is being shot with perfect form.
"Is there a certain amount of nock travel coming from a single cam or can one tune to take it out on a single cam?"
Most bows have some combination of vertical and horizontal nock travel. Some can even be induced by the shooter. To tune it all out is frequently impossible. It is therefore a waste of time to merely find the spine of the arrow if you don't know where to orient it. Shooting through paper with a bare shaft does both at the same time. Once you find the optimal nock orientation then adjust the rest and/or nocking point to shoot bullet holes as far out as possible.
A guy named Shane Chuning is very knowledgeable on the topic and has tested hundreds if not thousands of arrows. He also has a website called ontarget7.com
It would be great to buy a RAM spine tester, but I can't justify the cost. There are a few online arrow dealers now offering this service and mark each shaft's stiff side. I may go this route in the future.
There is definitely a noticable "wobble" if the spine is orientated to anything but optimal, but it's more of a nuisance than anything else I think.
You don't have to do it to bowhunt. Plenty of guys don't. But why wouldn't you want to be more accurate? I try to be as accurate as possible. I have found that I have increased accuracy when I have my arrows indexed.
Here 2 arrows at 110 yards I shot the other day. I shot this just for fun. Makes me better for 30 and 40 yard shots.
don't we all man, don't we all.................
Plenty of them don't and actually laugh at the idea. I know, I know, spine indexing is all the rage these days. Pretty soon it'll be something else that suddenly no one can do without.
Now, where did I leave that Acorn Cruncher? Maybe it's next to my Ozonics machine. ;)
To say that aluminums don't have a stiff side would be incorrect. It's generally the weld seam.
A hooter shooter will confirm all of the above. Will it make the difference between a hit or a miss, not likely but it'll make a difference.
Now, if I get an arrow that is consistently out of the group, which is rare, I just rotate the nock.
But then, I'm not a great shooter either.
Anyone ever see post where they talk about bh tuning saying they can't get their fixed heads to fly the same so they just use expandables as a simple fix. Bet if some of them tried what we are discussing they would see positive results. Just food for thought.
To those of you who don't do it I'll challenge anyone to step up next to me an ermine an go head to head in a bh shootout. Myb you'll change ur mind.
I'm not convinced it makes a HUGE difference but archery is a game of inches and paying attention to the finer details will make you a better shooter in the end. I need all the help I can get when "buck fever" settles in!
For those who are unfamiliar with the construction of carbon arrows: picture a wet mat of carbon/fiberglass fabric that is wound around a center rod (called a mandrel). The fabric is wrapped around the mandrel until it hardens and then the mandrel is removed. This leaves a hollow carbon/fiberglass shaft.
When the fabric is wrapped around and the shaft is finished there is normally some overlap. This overlap of the wrap makes for a stiffer side, this is normal. If the number of wraps lines up perfectly then the shaft won't have any stiff side and will be perfectly consistent, this is rare. I did a google search for images and couldn't find any so here is a quick sketch.
Of course the shaft manufacturers all strive for a perfect number of wraps without an overlap but since the fabric is flexible it is very difficult to gain perfect control on mass manufacturing equipment.
Arrow shafts, golf clubs, fiberglass pipes, fishing rods, etc are all made the same way.
When I was in the fishing business years ago it was obvious where a fishing rod was assembled. If it was made in the US the handle and guides would be on the stiff side of the blank. If the rod was made overseas the handle and guides were positioned at random from one rod to the next. At that time only the US manufacturers paid attention to the stiff side of a rod's blank. Overseas manufacturers simply didn't care because the consumers mostly didn't care. Rod manufacturers have known about it for years. Ever notice how some fishing rods cast more accurately than others? This is real, folks.
I'd rather index my arrows than watch TV.
Good info.
RC's method sounds great. The carbon's overlapped side should settle downward because it's heavier and then you mark the top.
What is dynamic spine indexing?
Not saying there isn't variation in spine in nearly any material, just not the way some are using the term.
You are still indexing the shaft, just not to the stiff plane.
RC....... Have you compared your float method results on a RAM tester? Not looking for an argument, just asking. At one point, I used to look inside the shaft with a light and was able to see the beginning of the wrap (GT arrows) and would mark the shaft to fletch them the same way. Don't really know if that helped or not. The last batch I bought was hand selected out of 2 dozen that had the most consistence spine around the shaft, so I didn't index them prior to gluing in the inserts. I may still try the float method.
A spine tester can kind of work but what really matters is how they react when you shoot them. Gillingham does it with every arrow he shoots and he's the longest tenured employee at Gold Tip. Not too bad of a shooter either.
They do not shoot for a clean hole thru paper; they shoot for the same tear. I don't know anybody that after tuning, has a bullet hole in paper. Grouping is what matters.
IMO the indexing would become more an issue if the spine was marginal to begin with. The less the arrow flexes at launch the less a bit of variance in spine from shaft to shaft (or within a shaft) will matter.
I have a tool I made years ago with bearing rollers on the end and a dial mike in the center. Made it back in the day for checking and straightening aluminum shafts. Have used it with a "sling" and weight similar to the RAM tool for spine and "indexing" carbons. But honestly haven't used it in several years. I can't remember having such issues in a some time now with "fliers" shooting stiffer CTs and Victorys. Maybe I'll check the next batch.
Don't make any adjustment yet. Shoot several more arrows before you come to any conclusions.
BTW....... I'm far from an expert here. I've had difficulty with shooting bareshafts in the past, but I can get FBBH's to shoot with FP's out to 60yds usually too. I know a persons form had better be spot-on and minimal facial contact to achieve good bareshaft results.
You may have to put a dab of lipstick or oil on the point to help determine which end of the tear is which.
A bullet hole thru paper isn't a tuned bow and prior to extruding, the aluminum coil is welded during the tube forming process.
Coccon, black eagle doesn't mark the spine side.
An aluminum arrow's final shape is determined by a die via an extrusion or drawing process, not a welding process. The aluminum was at one point liquid and cast into a billet. You wouldn't say the arrow tube was made by casting. Well, maybe you would, but I would not. My aluminum arrow show no evidence, inside or out, of a weld.
I spent the day in Eastons plant, they buy coil stock, run it thru a former that forms it into a tube and welds the seams. It gets cut to length and then goes theu several extruders. The weld is always present and visible to the naked eye.
Groups are more a function of the shooter than the tune of the bow. A shooting machine will shoot virtually same hole groups with a moderately untuned bow.
The tube manufacturer that I am familiar with extrudes the tube from a very hot billet under extreme pressure. I wonder if Easton has changed their process since you were there for there is no visible evidence of a weld in my shafts. Maybe the extrusion process rubs it out.
If you're confident in your tuning, stick with it. When you have some spare time I'd say dig into group tuning and see if it does anything for you.
For me, paper tuning s the beginning of the tune, and a "rough" tune. I simply tune my broadheads to impact exactly with my field points and for the smallest group I can.
I do not index my arrows. Unless one does not shoot to he same poi as the others. If it still doesn't impact with the other arrows, then I put a judo tip on it and expect to break or lose it chasing grouse. If indexing it differently does bring it into the group, then I may refletch it, or I may just use it for field point shooting and never for hunting.
Indexing the spine of the arrows may allow a person to use a couple more arrows for broadheads. Or for a person to still get use from arrows with a slightly weak spine. Or tighten a shooters group a little giving them more confidence in their setup. That confidence would be the most important in my opinion.
Then he wasn't well tuned.
In all honesty I see paper as a very rough tune. A starting point to tune. And if getting tears that's not a good starting point.
I don't know what target shooters do WRT tuning. I do know if you're getting any kind of tear in paper you aren't going to get broadheads grouping with FPs. The FP won't care much about the air they catch. FBBH are in your face about it. If they aren't both coming off straight (bullet holes) FBBH will let you know real fast.
Broadhead tuning (grouping FBBH and FP to the same point) IMO is the holy grail of tuning for bowhunters. There are several ways to get there, to have both grouping to the same point... but to me that's the final test to pass.... if it's not there it's not tuned.
When you broadhead tune you compare the flight of a stable arrow, the fletched field point one, to a less stable arrow, the fletched one with a broadhead. The quality of the tune depends upon the actual difference in the degree of stability of the two arrows.
Is the only difference the broadhead or do the have different fletching and different FOC too? Assuming everything is the same except for the head, how big is the broadhead being used? Obviously the bigger the broadhead the more unstable the arrow and the more accurate the tune will be. So the "Holy Grail" of tuning actually depends upon the size (surface area) of the broadhead used. A rather subjective way of doing things in my opinion.
Shooting through paper with a bare shaft, on the other hand, is the ultimate in an unstable arrow. (Shooting a broadhead on a bare shaft is more unstable, but potentially too dangerous for Easton or myself to recommend) Being able to produce a bullet hole at 5 yard increments out to 20 yards demonstrate a the very definition of a tuned bow and under more extreme conditions (more unstable) than broadhead tuning.
A moderately untuned bow can shoot a clean hole through paper at 20 yards with a broadhead tipped arrow. The arrow has time to stabilize because of the fletching. Not so with a bare shaft. Unless the bow is in tune and one's form is near perfect, a bullet hole is impossible with a bare shaft.
There are many good tuning methods, but some give more accurate results than others.
(Easton's paper tuning method at 3 and 10 feet with a fletched shaft and their "bare shaft" tuning are not the bare shaft through paper tuning that I speak of.)
Just asking cause I'm curious. I have never walk back paper tuned. I have always just got a bullet hole at 6-10 feet then moved into BH/FT grouping together tuning. I do not index my spine either.
The only bad thing about this method is that it requires near perfect form. Tears can be due to form rather than the tune. You should take 3-5 shots and get consistent tears before making the appropriate adjustment.
Bad form affects all tuning methods, but this method is more sensitive than the others.
That is the test if you will. Get there any way you wish. But no matter how great one thinks their arrow flight is if that criteria isn't met... it's not tuned well enough. If your method produces that end.... good to go. If not....
I like to use the biggest broadhead I have at hand, normally a big old original snuffer. Once that is dialed in I have yet to find a head that doesn't hit to the same point inside 50 yards or so. I'll have two or three different broadheads in my quiver sometimes. Doesn't matter which I shoot.
I've owned more bows than I should probably admit to over the years. Let's just say it's passed double digits a couple times over. ;-)
I have never done anything other than paper tune. I've never walked backed, I've never bare fletched, I've never BH tuned, or anything else. I've always figured if I can get a bullet hole at 6', 12', 5yds, 10yds, and 20 yds, that tells me my arrow is flying pretty darn straight. If my arrows are flying pretty darn straight, that means that my BH should fly same as my field tips. So far, that's been the case. Hell, maybe I've just been lucky. However, that luck's served me well for over 30yrs, so I can live with that. As TD says, doesn't matter what road we take as long as we get to our intended destination. If not, better take a different road.
Skimming through this thread it seems most posters are correct and debating semantics. Here's my take:
First off, the water float method does not work. That method only finds the side with the most resin. Resin doesn't make the arrow stiff, the carbon fibers soaked in resin make the arrow stiff. (Four inches of concrete with two layers of rebar is stronger than six inches without rebar). The only real way to mark the stiff side is with a spine tester. I made my own out of a $20 dial indicator. Take your dozen bare shafts, find the stiff side, excluding any shafts that are not within your own parameters of consistency with the other shafts. Once you have them all marked, take one or two to the range and shoot them through paper at increments out to 20 or so yards. Tune and adjust your bow until you have the smallest tear you can. Now, turn the nock until your bow finds the smallest tear in those arrows. At this point you have found where YOUR bow with YOU shooting likes to have the stiff side of the shaft located. Fletch accordingly and proceed to broad head tuning.
FWIW, not all carbon shafts are wrapped in layers like the pencil drawing posted earlier. My favorite shafts are made with a cross-weave carbon thread. Instead of wrapping "cloth" around the mandrel, the carbon thread is wrapped much like the line on your bait casting fishing reels. This method eliminates the starting and stopping points shown in that illustration.
One of the reasons I started using Carbon Tech arrows was that they used the cross-weave method that I prefer. And unlike the other companies using that method, CT does not "grind" their shafts smooth after coming out of the machine, exposing carbon fibers. Most of the time, I am unable to determine a "stiff side" of CT shafts.
I used to buy my CTs through x-man....
Anyone with any info if the newer overseas built CT models are the same quality as the old made in USA models were?
Wood that is an interesting test. Makes sense. Although it may not give exact location of the "stiff" spine as you're right, it could be 180 across, I'd bet just having it aligned on one plane would be enough.
YouTube and the Internet has some good and cheap ideas.
Just curious, which side are you marking as the stiff side, the concave side or the convex side?
They have the same machines overseas that were used here. When the production was sent over, they literally packed up the US plant and shipped it over. The difference is, now the plant can run 24/7/365 for about the same cost as the single shift did here operating on a normal schedule. What I don't know, is if the operators have the same attention to QC.
When the plant was here, I threw away one bad shaft for every 20 dozen or so. Seems like now, there is one "flier" in about every 5 dozen. With most of the flaws coming in the ends. If you have enough length to remove an inch from each end, you shouldn't have any "fliers".
I still have two dozen shafts on hand, and when those are gone I'll have to start paying retail like everyone else. :(
I wonder why arrows and fishing rods alway bend in the same direction. If the weak plane is in-line with the convex and concave bend, why doesn't the arrow and rod show an equal tendance to bend both direction along that "weak" plane? They don't, they alway want to bend in the same direction. In fact, the outside (convex side) seems to shows the most resistance to bending. So I would call it the stiff side.
You both agree that the stiffest spine is 90 degrees to the weakest plane, but did you go 90 clockwise or counter clockwise?
The shaft always bends in the same direction. What you mark as the weak side is consistently the weak side. Right? So the opposite side, in the weak plane, must be stronger than the weakest side. You are saying that this side that is 180 degrees from the weakest side it's not the strongest side, however, logic says that it must be stronger than the weakest side.
So does the strongest plane (the one 90 degrees to the weakest plane) also contain 2 different strengths? How did you determine which side is the strongest in the strong plane?
The same goes for tuning your bow. You want arrow flight that is free from porpoising and fishtailing. Only slowmotion photography or shooting through paper actually shows proof of the trueness of the arrow's flight. Broadhead tuning only shows that the broadhead tipped arrows are grouping with fieldtip arrows. It does not show the actual trueness of the flight. That you are just assuming.
I understood that you think the heavy side is the stiff side. It is not. By using both the water float test, AND an actual spine tester on the same dozen shafts, the marks don't line up. So what you are finding by floating in water is only the heavy(weight) side of the shaft, not necessarily the stiff side.
In what way would a FBBH be considered launched perfectly if it DIDN'T hit with the FP? What you are getting is decent flight once the fletching stabilized the arrow off the bow. But the head is catching some air at release and starting to plane right off.
I have yet to use (as in ever) any tuning method to rough tune and then finish fine tuning using the broadhead method... and not still have perfect results with the previous method used... including paper, bare shaft, walk back, etc. Nor has any grouping opened up when finished broadhead tuning. But when I was done I could screw on pretty much any quality broadhead and they would all hit together. And right with the FP.
IMO, for bowhunting/fbbh, that's tuned. I've read the grouping theories held by some target archers, but they are not shooting broadheads. Much less a variety of heads, including FP and judo heads.
Again, much of this whole spine indexing thing (in a modern compound bow) can be reduced to near irrelevance using a spine on the stiff end (or higher) of what the "chart" recommends. The less an arrow flexes at launch the less importance any "indexing" will have. With modern compounds the whole idea is to eliminate flexing as much as possible.
Trad is much different, where you tune arrows to a bow which is very limited as to it's adjustments and have a finger release to deal with. The right arrow build likely more important than the bow. I remember building wooden arrows back when, that is actually where indexing was at it's most important level, right after separating shafts as to general spine, no two shafts being close to exactly the same in nearly any way. Much less of a problem with carbon, but still the potential for an issue as you will normally have a good deal more induced flex as you tune your flex to the bow.
Compounds you should be using an arrow that essentially eliminates the shaft as a variable and adjusting/tuning the bow components to shoot that arrow with as little induced flex (or nock travel both vertical and horizontal) as possible. That is your "perfect" broadhead launch within the capability of your equipment and form. Tuned.
It's that phrase "hit to the same point" is a big part of the problem. Everyone says that, but they don't. What really happens is you shoot a group. If you shoot a 3 shot group and determine it's center, it won't be at the same point as if you shoot a 5 shot group. And that center won't be the same as a 20 shot group. Each will be a little different and the bigger the sample size the more accurate the results. So the accuracy of the tune varies with number of shots in the groups.
"FP lie. They shoot with the very least amount of plane and fletching requires a minimal effort to stabilize."
Yet this is the flight that you try to duplicate??? Why would you do that? That "minimal effort to stablize" is a sign something is wacky. You are tuning to a "control" or "standard" that required stabilization.
Broadhead tuning is great, just not the best. After you BH tune remove the fletching from on one of your arrows and shoot it through paper at 20 yards. Replace the weight of the fletching with masking tape if you want. See how true your flight really is.
The real message here is to use some form of tuning. They all work just fine. Don't just slap on a broadhead go hunting.
Next onto BH's and serious distance walk back tuning. The 3D league will never be the same.
I used to do that for my customers @ $2 per arrow. Not as many as you would think took me up on it. It took a couple hours extra per dozen shafts on average. Most guys thought it was a rip-off, even at $12 an hour.
It would be better if guys would learn to do it themselves. I/we never came out ahead by pre-fletching arrows anyway. I would have preferred to sell bare shafts to everyone. That would have saved me at least two hours each night.
So your groups don't hit together?.... you reconcile that exactly how?
Why not? They should. Or what do you do? I would say if they don't it is you that have the problem and are compensating for them not grouping together. "Just sight in for broadheads" is right in the same realm as "just screw on a mech head..don't worry about it...."
I'm good to 70 no matter what I screw on to the shaft. Two animals over 60 this year. Shoot FPs for practice. Shoot a FBBH group once a week or so to make sure things are still good. But been a slow year, only killing animal a month or so.... 4 deer this year. I bowhunt every week. All year.
I understand the physics debated and how "exactly" you make your case. If you want to discus micrometers that's all well and good. I get it, drag and coefficients, but fractions of aerodynamic differences matter little for dialed in broadhead accuracy. If I'm 1/4 inch off because of aerodynamics at 45 yards I can live wit it.
I like to discus animals on the ground. Classroom esoterics I have no interest in. I get the theory, in some classroom setting debating over fractions of an inch. But it has no relevance WRT to killing things with sharp stick. Unless of course you have some real world, in the field physics to go over?
So how do you dial it in to kill things in the field? Your groups do not come together? Why not with less than hooter shooter accuracy? I'd say you weren't tuned as how would they not given "perfect"tuning?
How else would you reconcile the physics that they DON'T group together? Leaving your micrometer at home...
However, I too shoot Carbon Tech per X-Man and although never attempted extensive measurements, could not detect a differential spine.
Randy Ulmer wrote an article several years ago in which he likes to try to "force" the arrows to all begin flexing in the same direction for consistency. He ties a nock point inside and at the bottom of his D-Loop so that the string puts a downward pressure on his rest at full draw. He said he felt that it helped all arrows begin to flex in the same direction upon release/load, thereby giving more consistent launch and arrow flight.
Carl
"But spike, if the stiffest side bends the least, then it has to be 90 degrees to the side that bends the most. The convex side is bending and the concave side is bending. the sides that are 90 degrees to the bend are not bending at all. "
I'm sorry, but that has to be the dumbest statement on Bowsite since TBM left.
When an arrow shaft bends, EVERY side bends. Every single molecule around the circumference of the shaft is moving.
I took my spine checker apart and repurposed the dial and frame simply because it became an unnecessary step.
If the clamp method was consistent, I can see marking the shafts and fletching the cockfeather matching on all of them But I would still rotate nocks on flyers.
I used to worry about indexing spine, but it doesn't really matter that much. A bow in sync matters more.
'Nuff said.
The carbon fibers are still either in tension or compression, regardless of a weave or rolled pattern. But to say that the side of an arrow that has more weight doesn't mean more rigidity isn't necessarily correct either.
Something in the case as a rolled shaft would have more material at one spot than any other place, structurally, a "strongback". That would give a higher rigidity for the arrow, aka, spine.
More material is just part of it. The shape of the material has just as much to do with its stiffness.
Also the material's compression modulus vs tension modulus is a factor. Carbon composite's tension modulus is about 10 times its compression modulus.
In the drawing i found on the net, i believe bending about the X axis would be more rigid than about the Y axis.
But next time I buy a dozen shafts, I'll cut 1/2" from each end. Then using a ball bearing, of about 3/8" diameter, on each end, I'll "compression" test each one. The ball bearing will stay concentric on the ends of the shaft and the perfectly round shape should impart no bias, from the compression device, to any direction. The compression device should also have hard, metal surfaces.
It would make sense to me, that if you have shafts that CONSISTENTLY "hump" the same way. to fletch so that the shaft flexed up away from the rest. And certainly not to one side or the other.
Sound reasonable?
As for end loading the shafts, I can use the lathe chuck and live center. That should be about as accurate as possible. And I don't think gravity would have a measurable effect on the result. But that is easily tested to.
Also, I wonder if the compression test would better simulate a dynamic spine?
But this is interesting and thought provoking entertainment between spring bear and fall hunting.
Although the drawing is exaggerated for an arrow, it illustrates the point that more material on one side can cause it to be the stiffest part of the shaft, assuming the manufacture was rolled.
If more material causes more weight, I would conclude that floating an arrow is a method that can be used to show which side may be the stiffest. Is it as accurate as a spine tester? No, it is not.
Yes it is interesting to overthink this stuff. It dosen't make a dimes worthof difference to most people.
"Although the drawing is exaggerated for an arrow, it illustrates the point that more material on one side can cause it to be the stiffest part of the shaft, assuming the manufacture was rolled."
Not necesarily. As I said, it depends on the shape of the material too. In other words, where the material is located in relation to the bending axis. The arrow will flex about an axis that goes through the centroid of the plane of the cross sectional shape, not necessarily the diameter of the OD or ID. The material that is located furthest from this axis has a greater effect on the moment of inertia than material close to the axis.
Therefore, in the above drawing, I believe bending about the X axis would be more rigid than about the Y axis, because of the location of the majority of the material. Just like a 2x4 is more rigid when placed on edge to the load rather that flat to the load like a diving board.
HDE, I don't know if we agree or not. You say the side with the more material is stiffest, but you don't say which direction that you assume the load is coming from.
In the illustration above, is the shaft more rigid when loaded vertically or when loaded horizontally?
Just a one word answer is all that is needed to my question....vertical or horizontal.
I feel I'm more thorough than your average bowhunter getting my stuff dialed in, but dang, there's always that guy that makes you feel like you're not doing much.
I've always just bought 2 dozen arrows at a time, shot them all repeatedly, and picked out my favorites for hunting.
Food plots, underwear, backpacks, manscaping, it's all relative. Take your pick.
The column loading of an arrow, when shot from a bow is not as precise as loading it between centers in a lathe. A bow may also induces vertical and horizontal forces due to nock travel and cam lean. Besides, in reality, we never know where the thick spot or thin spot is or the actual direction(s) of the loading that is placed on the material as it leaves the bow.
For all I know the carbon fiber mat may start as a parallelogram or trapezoid. The edges would then spiral as it is wrapped around the mandrel. Because of all the unkowns is why actual shooting of the arrow is important if you really want to know if indexing the spine has any benefit or not.
You said "the sides 90 degrees to the bend are not bending at all"
That is the part of the statement that made me laugh out loud and spit my beer. I hope to God that was a typo, because only TBM would be that dumb.
P.S. Grampa always said "It's better to be a smart a$$ than a dumb a$$" and don't worry, I'm quite used to being the smartest one in the room ;)
FWIW, if the "stiff side" of the front half of the shaft is the "weak side" of the back half of the shaft, it will twist as it bends. So NO, there isn't [always] one straight plane.
I think the problem is Wood isn't saying exactly what he means. I THINK what he means is that the "sides" are not being bent in a plane or direction that tests their rigidity. They are only being bent in the weakest plane and in only one direction in that plane.
Kind of like column loading a 2x4. It will always bend in the direction of a 4" side, but that does not mean the the opposite 4" side offers the most resistance to flexing for it too was bending. It just had more resistance than the other.
Now, as far as a shaft twisting as in a post above, I don't buy that one....
Why is it reasonable?
After all the in depth discussion, postulation, speculation and even some accusation, I think Wood has nailed the practical take-away from it all.
If you can reliably predict which way your arrow will "hump", then it stands to reason that you can mitigate for at least one of the variables that archers encounter.
I just may check a dozen of my finished arrows and mark them. Then see if rotating nocks for that orientation tightens up groups.
The inside of the bend is the smallest radius of all the material that is being bent. Therefore I would think that it would be the one that "bends more", because it does. Why would the stiffest side, which you claim is on the inside of the bend, want to "bend more"?
An arrow that is bent over the outside of a car tire sees more stress than if it were bent over a tractor tire because it is "bent more" by the car tire.
If you bend a pencil a little it will flex. If you continue to "bend it more"., thereby decreasing the radius of the bend, it will break.
The smaller the radius that the material is bent, the more stress the material will see. Therefore the inside of the bend of any material "bends more" than the material on the outside of the bend.
Some folks seem to be confusing tensile and compression, using them interchangeably. When actually both forces are at work here but on opposite sides of the shaft.
At this point I'm willing to accept Wood's "compression" principle and application as it is physically demonstrable and easily applied to possibly enhance consistent arrow launch.
I had an insert with a field point in each end as per Woods instructions, but when I spin-checked the shaft, there was a slight wobble at the point of each end(darn field points aren't perfect). ... So I spun the inserts 180 degrees in the shaft, and wouldn't ya know, the high point of the bend moved to the other side of the shaft.
Disclaimer: I was testing Carbon Tech shafts, so there may not be as much of a difference between the stiff side and the weak side on these.
If a 1.57 foot long tube is bent around a 1 foot radius it will undergo about a 90 degree bend.
If the same tube is bent around a 6" radius it will undergo about a 180 degree bend. 180 is more than 90 so the smaller radius bend is "more of a bend".
Smaller radii give more of a bend. It's more in degrees and it's more in stress, so it's more of a bend.
