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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 15, 2024 05:03PM

The spine, if we're referring to the softest axis, is rarely if ever going to be on the natural curve which is the straightest axis. And if you build with the curve "up" that certainly isn't going to be the softest axis - it's going to be the stiffest axis.

Now if he is building on the softest axis, then it's time for data and practical tests to indicate why that's the better orientation.


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Re: Spine of Rod
Posted by: Robert A. Guist (---.res6.spectrum.com)
Date: January 15, 2024 05:15PM

Hello All.

Here are a few of the stories about "spine"

16/2 Spine Legacy: A Magic Wand. By Rich Forhan. 30
3/4 Spine, Another Way To Find It. By Don Morton. 18
2/4 Spine. 16
6/1 Spine: Playing With Rod Spine. By Rich Forhan. 14
13/6 Spine?, What About It. By Tom Kirkman. 24
19/6 Spine?, What About It. By Tom Kirkman. 12

Ya'll enjoy now (here we go again)..

Tight Wraps & Tighter Lines.

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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 15, 2024 05:38PM

So now we’re back to what can actually be proven with either build orientation -

On the stiffest axis we know that you have the maximum deadlift capacity in play when fighting a fish. We know that you have a bit quicker response (rod speed). It appears, from what anyone can tell in absense of any practical test, that casting is just as accurate as if the rod was built on any other orientation.

So what advantages does building on the spine offer? It doesn’t stop rod twist. It’s the weakest orientation and there is no proof that casting accuracy has been increased. So what is it buying you? You could prove that building on the spine results in a slightly weaker rod but I’m not sure that’s a good attribute to argue in favor of, particularly when so many fishermen these days use their rods like derricks to lift and swing their fish into the boat.


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Re: Spine of Rod
Posted by: chris c nash (---.atmc.net)
Date: January 15, 2024 07:51PM

I would seriously consider a sticky on rod spine , something in the library that thoroughly covers it instead of just how to build a spine finder . We shouldn't have to go multiple pages every time the question about rod spine is asked because it's the exact same arguments and counter arguments every time and most newbies aren't familiar with the archives.

I will say this , as highly respected and brilliant as Gary Loomis is I agree with Tom on this and have come to the same conclusions as he has . No matter how I have oriented the spine on my builds I have never ever noticed any difference whatsoever in the performance and I've tried to notice a difference and there just isn't any in my experience and I only build spinning rods .

I have built spinners exactly how Clemons etc.. has stated is the proper way to build them and I've built the complete opposite way and there is no difference . All have been exceptionally accurate and outstanding casters .

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Re: Spine of Rod
Posted by: Jeffrey Merlino (---.phlapa.fios.verizon.net)
Date: January 15, 2024 11:04PM

I use the human analogy myself. I think it's the most relatable and makes the most sense to me. Because people do carry different positions on which side of the curve is the spine, I try to stay away from it and relate everything back to an 'inside the curve / outside the curve" perspective. Regardless of which side of the curve is your spine/spline/perferred plane of bending/etc . . . I think everyone is finding it the same way: butt on a hard surface, tip supported by your hand, roll the blank with a bit of load until it "pops".

Okay Tom, with that is my backdrop, and quoting you above "spinning guides get placed on your back and casting guides get placed on your belly.", what side of the curve do fly guides go on and is there a difference in thinking between 5WTs and below vs. 6WTs and above?

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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 16, 2024 09:48AM


The quote you list above - "spinning guides get placed on your back and casting guides get placed on your belly" is not mine. But it does indicate the age old false idea that you can create a stable rod by where you orient the spine. The fact is, spine has nothing to do with rod stability. Any rod with the guides placed along the top will attempt to twist under load. Any rod with the guides placed along the bottom will be stable under load (thus the reason for the spiral wrap). And this remains true regardless of where you orient the spine.


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Re: Spine of Rod
Posted by: El Bolinger (170.63.67.---)
Date: January 16, 2024 10:12AM

@Tom I never said that building on the straightest axis makes the rod heavier

Building rods in MA, Building the community around the world

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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 16, 2024 10:22AM

I never said that you said that. In fact, such a statement wouldn't make any sense. The blank weighs what it weighs regardless of how you orient it. Most likely a typo somewhere.


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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 16, 2024 11:39AM

This might deserve a new topic of its own but I'm going to add it here so those newer to the craft can gain some insight as to where the stuff about rod "spine" came from and why it was wrong from the outset.

You will be hard pressed to find any mention of rod “spine” prior to 1974 when Dale Clemens wrote about it in his first book. At the time he used the term “spline” (a holdover term from segmented bamboo rod making) and later changed it to “spine.” It is fair to say that it was Dale that either created the concept or at the very least popularized it to the point where it is today.

In the Clemens book Advanced Custom Rod Building Dale Clemens made these statements:

“Lure weight loads the rod in the cast just as the hand loads the blank in a spine finder" and “A good rod builder takes care to mount the guides on the blank’s effective spine to prevent it from twisting when a fish is being fought.”

So the intent of a particular spine orientation has always been to supposedly improve casting accuracy and prevent rod twist when fighting a fish.

But this is where Dale went down the wrong path. Loading the blank by hand pressure does not approximate loading the blank via a line running through guides which are attached to the rod. These are two very different scenarios and result in different outcomes.

Loading a blank by hand, the blank will rotate to its softest/weakest axis. Loading a blank via a line running through the guides, the rod will turn so that the guides face the load, regardless of what axis they are placed on.

Dale either didn’t understand the lever arm effect or simply overlooked it. Regardless of which, his failure to consider it dismantled the spine orientation argument at the very outset. Spine orientation can neither improve casting accuracy nor create a stable rod.


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Re: Spine of Rod
Posted by: Ernie Blum (---)
Date: January 16, 2024 01:07PM

The few fly rods that I have built over a forty year span have served me well. I have built them for line weights for pan fish up to line weights for Keys tarpon. When I built my first fly rod, my mentor explained to me the concept of finding the spine of the blank. The blank was a Fenwick two piece blank.

Finding the spine was a no brainer, but it seems that I misinterpreted the reason for finding that spine. Because I didn't know any better, I "logically" ( in my own mind ) took that spinal axis which I interpreted as the softest (weakest) axis of the blank, and found the axis 90 degrees from that axis. I made the assumption that THAT axis was the strongest axis of the blank, and that is the axis on which I assembled the components. My understanding now is that the strongest axis of any particular blank can be anywhere from "...90 to 170 degrees" from the spinal axis. In any case, I was making an attempt to build the rod on a stronger axis than the spinal axis, because in my mind the question was, WHY WOULD ANYONE WANT TO BUILD A ROD ON ITS WEAKEST AXIS?

The last fly rod I built was twenty years ago, long before I knew of this rod building site. So ALL the fly rods I have built were built in this "incorrect" manner. I have never been unhappy with any of those rods, but also have no idea how they may have performed if they were built in what has historically been considered the "conventional manner". But for me, casting distance has always been an issue. I'm in the scientific camp when it comes to stuff like this for sure, and in my mind, if "...for every action there is an equal and opposite reaction", why would a rod built on a stronger axis not be able to propel a lure or a fly line farther than the same rod built on its weakest axis? If it takes more force to load the rod, does the loaded rod then not exert more force in propelling a lure or fly line in the opposite direction, consequently resulting in increased distance?

And I just recently ordered a four piece fly rod blank for myself. My old system may have been wrong, but it was easy to accomplish! :-) I simply took each segment, found the spine, found the axis 90 degrees to that spine, and I had my mark for the guides on that segment. If I wanted to build the whole thing on it's spine, I could do that. But what about the "straightest axis" method? How many potential possibilities are there for mounting four blank segments together to make one whole rod with the end of each segment 360 degrees around? Are there any tricks for honing in on a "straight" blank other than through trial and error?

I think my head is about to explode. I am eager to hear from Tom after speaking with Gary about this subject. And for the record, if I had to interpret that video of Gary Loomis explaining where he would place guides on a blank, it seems clear to me that he is simply finding the spine of the blank, and suggesting that spinning guides will go on the concave side of the blank while in its flexed (stressed) position, and casting guides would go on the convex side of the blank while in its flexed (stressed) position. In essence, he's suggesting the guides go along the weakest axis of the blank.

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Re: Spine of Rod
Posted by: david taylor (---)
Date: January 16, 2024 02:12PM

The spine debate continues, IMHO a mixture of myth and some fact, in many instances with little relevant scientific or measurable support. The dead lift measurements at least provides concrete data as to strength properties. The fact the many rod builders debate this issue points to the lack of significant good or definitive science and/or understanding behind the issue.

I suspect most started building on the spine so that the final product might appear straighter looking to the buyer when eyeing the rod, as if the rod were bent to the left or right one might dismiss it for being crooked. If it bent slightly up or down, it would appear straight., and gravity would mostly pull an upward bending tip down anyway.

The spine issue is further complicated and confounded when you add in multi-piece blanks, especially 4-piece fly rod blank, which is my building focus, sometimes built on 4 different mandrels.

As indicated by Tom, any carbon fiber tube or rod blank will have an area where the wall is thickest and thinnest, and that strongest or straightest axis might not necessarily correspond 180 degrees with where you mark the spine in the flipping exercise. In fact, in most cases it will not. Other methods can be utilized to determine the strongest or straightest axis in a blank or tapered graphite tube.. Some of these are often employed to determine a golf shaft's straightest or flattest axis for alignment in custom fitting. While the physics indicates such alignment should theoretically make a difference, and many golfers swear by it, actual testing of dispersion (consistency) on golf shots or shot distance typically fails to show a significant, real-world difference.

I would suspect on most modern multi-piece blanks you would not notice a casting difference in terms of accuracy or distance regardless of how you aligned the guides, as quality blanks these days are made quite well. Just for fun I was trying to test a blank section of a fly rod for its spine last week and it was so straight it was proving difficult, much more so that in past rods I built.

Any graphite or steel tube or blank will have a certain degree of torque. As suggested, the line running through the guides, especially when casting or fighting a fish, will serve to keep the rod in the alignment the guides created and torque would not be an issue.

As to spine finder devices, I would suggest avoiding them. Just for giggles and investigation, I constructed one of high quality bearings and a PVC tube. It functioned quite well in finding what we would call the traditional spine, but the pressure placed on the blank by the bearing created a weak spot, and both blanks that I used in this device wound up snapping where the bearing had made an undetectable to the eye micro-fracture or weak spot in the blank wall. So if you use such a device, you had better tape well the section of the blank interacting with the bearing.

Rod companies are not 100% in agreement on spine alignment. Two recent folks I spoke with said they rely on a straightest axis method, another on a particular individual method he has devised. Others, such as T&T, have video of them finding the spine in traditionally flipping manner.

Edited 1 time(s). Last edit at 01/16/2024 06:37PM by david taylor.

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Re: Spine of Rod
Posted by: Mike Ballard (---.ip-54-39-133.net)
Date: January 16, 2024 02:28PM

If you build on the spine either on or opposite of it, then the rod will appear crooked to anyone that sights down it with the guides either straight up or straight down. If you build on the straightest axis and put the curve up, the tip will be high and will go down to about straight when the guides, thread and finish are added. I think this is another advantage for building on the straightest axis plus the straightest axis is usually the stiffest axis as well. I want all the blank can give and that would be it. It seems to me that spine proponents have spent 45 years basing their choice on something that Clemens wrote that was wrong to begin with.

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Re: Spine of Rod
Posted by: david taylor (---)
Date: January 16, 2024 06:48PM

Mike Ballard:

I would tend to concur. As I got back into rod building a couple of years ago, more than 30 years of a gap in between, I spined the first few rods I mad and then, after getting into this forum, and also with lots of graphite golf shaft experience in club building, I delved greatly into the issue and question.

I have ditched the spine method as historically defined and now work on the straightest axis, or in what golf would term the Flat Line Oscillation, which is pretty much the same thing.

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Re: Spine of Rod
Posted by: John Santos (38.22.141.---)
Date: January 16, 2024 09:29PM

Except, I have an All Star rod from the 90’s (they used taller guides back then), built exactly opposite of the spine, and it DOES have a twist tendency in your hands. That twist is negated the heavier the reel is, and without a reel it’s really obvious. I simply explain both theories to everybody I build for, and sometimes show them this rod to demonstrate the difference, and 100% have chosen to build on the spine. Everyone I build for are serious tournament fishermen so if they even THINK there’s a functional difference, they will pick that over aestethics all day long. Maybe it’d be better to let customers choose rather than continuing a debate that doesn't seem to be swaying people from either camp.

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Re: Spine of Rod
Posted by: david taylor (---)
Date: January 16, 2024 10:05PM

I only build rods for myself, so I have the luxury of only one customer. If you are a custom builder you must take customer desire, satisfaction and bias into consideration. And bias is a very real, but non-fact-based phenomenon..

Torque in a rod blank is the same thing as torque in a golf shaft or any tube. In golf, torque is defined as "a measure of how much a shaft resists twisting during the golf swing. It is measured in degrees, which denotes how many degrees the shaft will twist under a given force." In golf a high torque shaft twists at most 4-5 degrees. A low torque shaft 1.5-2.5 degrees. In real-life blind tests golfers were made to hit the same golf club head with the same weight shaft, but the they hit shafts that had a low, medium or high torque rating. One would presume the higher torque shaft would have greater dispersion, i.e. less accuracy. In real life tests it did not. The low torque shaft was hit with the same accuracy as the higher torque shaft.

In a quality golf shaft or rod blank the torque is low enough that a typical angler will notice no difference in casting based on torque, and the fact that a line is running through guides will theoretically prevent twisting even more. I have not seen a rod blank's torque rating, but with today's quality carbon fiber it will be minimal. And unlike golf, where the shaft is turned or rotated some in the golf swing, in fishing the blank is pretty muck moved in one back and forth plane, in the same orientation, thus not introducing much force to induce torque.

Your 1990s rod either had an incredible amount of torque, or its blank was twisted in a bit of a corkscrew manner.

The orientation of the spine and guides on the blank will not affect its torque, but could affect other measurements.

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Re: Spine of Rod
Posted by: Ernie Blum (---)
Date: January 17, 2024 10:43AM

Tom Kirkman Wrote:
> The strongest/stiffest axis is usually found along
> the blank's straightest axis.

Tom....I have seen this statement appear time and time again. Assuming it is true, what is it that results in the "straightest axis" of a blank, and what is the correlation between the answer to that question and it being the "strongest" axis? Also, I have seen the statement worded slightly differently on a number of occasions....ie....the straightest axis is "usually" the strongest axis, or, the straightest axis is "most often" the strongest axis. If there is a true correlation between the two, why isn't the straightest axis ALWAYS the strongest axis?

By the way, I'm not challenging you on this. I am however looking for a reasonable explanation of why this is so, as it is not obvious to me. And if I may ask, how can I apply this to building a four piece rod? Does one play around perhaps seemingly endlessly with the four blank segments until you finally find what looks like a straight tube? Are there any techniques that allow one to minimize the frustration that I envision?

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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 17, 2024 12:07PM


No problem - those are good questions. They are thoroughly covered in the article I often link to. Note in particular the side bar at the end of the article under the photo of a blank cross-section. I think it will answer your questions.



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Re: Spine of Rod
Posted by: Richard Bowers (---.ptld.qwest.net)
Date: January 17, 2024 12:34PM

I disagree with a lot of the prior posts - I have proven to myself (and customers, as well as students) that the "spine" does indeed affect casting accuracy. If the stiffest axis is 90 degrees to the left side (looking from handle to tip) the cast is pushed to the right of target by the rod trying to release to the softer side during the cast. The stronger the spine, the greater the impact. I have tested this repeatedly by putting guides on the spine and at 90 degrees to the spine on identical builds - the rod built on the spine (with the strongest side on the top of the rod) tends to release to the weakest side, and if that is in alignment with the bottom of the rod, the rod will be very accurate. I try to ensure the weakest side is on the bottom of the rod - on the guide side for spinning rods and opposite the guides for a casting rod. For a jigging or trolling rod (wherever the fishing method does not call for casting) I put the strongest axis on bottom to provide the most resistance to being bent - while the effect may be only in my mind, I feel better thinking my rod is that much stronger.

Be advised however that as noted in a previous post, the strongest and weakest sides are not necessarily at 180 degrees of each other, and there may in fact be primary and secondary spines. The cause of the spine is based on how a blank is constructed - the resin-impregnated cloth is tacked to the mandrel and wrapped under thousands or pounds of pressure. Where the edges of the cloth overlap, there will be an extra layer of cloth, resulting in the spine. This is mitigated in heavier rods where the number of layers is higher, as the percentage of the thickness where the overlap occurs will be much lower than with an ultra-light rod with fewer layers.

It is not unusual for a spine to rotate around the blank as the cut of the cloth could result in the edge of the cloth spiraling along the blank. If this is the case, a spine is very difficult to locate and its impact is severely reduced.

The spine has the most impact on a 1-piece blank. It also significantly affects 2-piece blanks, especially if the builder aligns the blank so the spines of the upper and lower sections match. 3+ piece blanks tend to mitigate the effects of the spine as the action of the cast is spread over multiple rod sections and there may not be a clear spine for the overall rod. Fly rods are also fairly impervious to a spine, as the rod action has little effect on the accuracy as it is the line that is cast, not a lure. The line will follow the path of the rod tip.

While this may be a minority opinion, it is one I have used for over 55 years and it has not let me down yet!

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Re: Spine of Rod
Posted by: Tom Kirkman (Moderator)
Date: January 17, 2024 12:52PM

While it has been well proved that the stiffest/straightest axis delivers the most deadlift power and that the lever arm effect of the guides trumps the spine effect, without some sort of mechanized device to deliver identical casts there is little ability to state with any certainly that building on one axis or another delivers better casting accuracy. Until such a device exists, casting accuracy is indeed in the mind of the caster.


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Re: Spine of Rod
Posted by: david taylor (---)
Date: January 17, 2024 02:21PM

Point well made and taken, Tom.

It would not be difficult for a company to produce a robotic machine that would cast exactly the same in every instance. In fact, such machines were created in golf years ago and are used by major manufacturers for club design and performance testing. I predict such measuring tools for rods will be developed in the next 10 years, especially as robotic costs decline, and will be used for rod design as well as casting instruction, and custom fitting. As will dopler radar based simulators.

I would think in fly fishing, which is my focus, the top level casters could cast and keep the rod within a few degrees of being on plane with regularity in a typical straightforward cast. You average angler, no way. Thus I think blank orientation in relation to casting accuracy is likely irrelevant to the average caster of a well made blank, just as a certain axis alignment in a golf shaft is not going to help an 18 handicap golfer hit straighter shots. For most casters or golfers it is more a function of one's technique than the blank or shaft's axis alignment. Even dispersion tests with PGA tour players who have their shafts aligned on the straightest axis prove statistically insignificant, thought some swear it makes a difference they can "feel" that difference.

But the science and truth of of physics do not lie, so it cannot hurt to align a blank or shaft on its straightest axis, but how much it helps in accuracy is yet to be proven. Lifting power is a different story. If one is concerned about casting accuracy, I would suggest focusing more on improving one's technique and staying on plane rather than obsessing on blank alignment, particularly in what we traditionally define as the spine.

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