With this blank I think since I can't find a dominant spine I will just build it straight.

Tom
i wont argue with you
but maybe there is difference in fisherman(customer) habit in US with in my country
and if you ask them about term of spine i believe in 100 customer ,0 has ever heard about it
because in here we used rod backbone term. LOL
i'm new to rod building and have read your article about rod spine above few months ago and your test in that article give me new perspective about rod backbone , since that time i tried to re-educate all my fishing buddy about it
but many of them still believe the rod that build in backbone is the best for fighting a fish

Tom,
Im just curious. Has there ever been any study or tests done on rod twist in relation to spine. Its my understanding that buildind on the spine will eliminate the rod rod wanting to twist when fighting a fish. I myself am dubious of this theory. I built several rods before I even knew what a spine was. Those rods fish just fine. Its interesting to think about what you said about the spine being the weakest part of the blank.
Barry

Barry, twist means torque/rotation. That takes a "lever arm". Think about closing a door. It takes a lot less force if pushed at the door handle and gets harder and harder as you move towards the hinge due to reduction of that lever arm.

If the fishing line moved through the center of the blank there could be no twist. The higher the line travels above the blank the more there can be. Heavy rods with tall roller guides can be seen to twist a lot when you catch a BIG fish.

The only force on the rod is the line. It decides what the blank does. A rod isn't going to do a 180 twist/flip anymore than a beam in a building would simply because one side is stronger/weaker. On the other hand put a bunch of eye bolts on the top side of the beam, string a heavy cable through them, pull sideways on the cable, and of course the beam would want to rotate.

Russ in Hollywood, FL.

Russ and Barry,

A little food for thought. We know that the blank exhibits this characteristic of a spine, and does have a preferred bending axis when the rod is loaded without guides. When you flex it along another axis, it wants to flex on that axis and you need to apply some amount of torque to keep it from doing so. That torque applies torsional stress to the blank. Once you wrap the guides, the torque from line acting on the guides will always overcome the torque provided by the blank. What it does mean is that a blank that is built off of the spine will be placed under more torsional stress than a rod that is built on the spine.

Many builders make an effort to reduce stress on the longitudinal fibers in the blank by performing static test when placing the guides. Yet, we often ignore the torsional stress applied to the blank, which gets carried by the scrim or fibers that provide hoop strength in the blank and are in lower number than the longitudinal fibers.

We know that materials fail when stressed repeatedly, so building off-spine gives you a rod that experiences more stress each time you fight a fish. Is this small amount of extra stress enough to lead to a higher failure rate than those built on-spine? I don't know. Repeated torsional stress will likely show up in a higher failure rate in conventional casting rods than that for spinning rods.

With all that said, I've moved from my stance that you should build on the straightest axis, to keeping it in the back of my mind. I doubt, as a primarily hobby builder that I will ever build enough rods that fail to build enough statistics answer the question definitively. If anything, the discussion makes an argument for building more spiral wrapped rods. The torsional stress applied by the line on a conventional casting rod will always be significantly higher than that on a spinning rod regardless of whether the rod is build on or off of the spine. Personally, I tend to build on the straightest axis and choose between spiral and conventional wraps depending on the application.

Joe

Barry

Yes. Tests have been done and confirm the physics of the matter.

For years I brought a demo device to the expo which proved that the lever arm effect of the guides trumps any spine effect. Consult volume 8 number 4 for the specifics.

Phil, that post was made in good clean fun. No cheap shot meant. Tom and I have debated this before and have agreed to disagree. Tom knows me and knows my style and knows that it wasn't a cheap shot, but rather, just ME.

Kevin Knox
ANGLER'S ENVY CUSTOM RODS
QUEEN ANNE, MD 21657
#_#_#_#_#
www.anglersenvy.com

Tom,

In general, a modulus constant for a material is modulus constant =stress/strain. Stress is defined as Force per unit of cross-sectional area, and the strain is how it deforms (change in length, angle of deflection, etc.) In order for a material to be elastic, there must be a restoring force supplied by the material. Your statement is the equivalent of saying that a spring attached to a ceiling with a mass hanging from it is not stressed. It is stretched to a length beyond its equilibrium length, and is therefore stressed. The same goes for an object that has a preferred bending axis. The rod wants to flex in that direction. You must provide some torque to flex it in another direction.

For the case of the spring with a mass, the elastic constant (k) is equal to the stress (weight of the mass, mg) divided by the strain (the change in length l-lo). For the rod blank, the analogous constant is going to depend on the torque applied, the moment of inertia of the blank, the diameter of the blank, and how the wall thickness varies around the blank. If the blank were uniform in thickness, it wouldn't have a spine, and it wouldn't have a preferred bending axis.

The condition you are referring to is static equilibrium where the forces are zero, or the for the case of the rod blank, the sum of the torques is equal to zero. Just because an object rests on an inclined plane without sliding, does not mean that there are no forces acting on it. It only means that the sum of the forces are equal to zero. The object on the inclined plane has 3 forces acting on it, gravity, the normal force between the object and the inclined plane, and the force of static friction. In the case of the rod blank, you have to consider the torques. You have the torque provided by the line acing on the guides, as well as the torque of the rod trying to flex along its preferred bending axis. The fact that the guides always win tells you that the toque applied there is always enough to more than overcome the torque of the rod trying to flex along its preferred bending axis.

Joe

Joe, strange I find myself with a different view on the subject. I could question a few of your statements but I'll focus on one.

"We know that materials fail when stressed repeatedly, so building off-spine gives you a rod that experiences more stress each time you fight a fish. Is this small amount of extra stress enough to lead to a higher failure rate than those built on-spine? I don't know."

You granted that the tension from the line would always be stronger than any forces from not building on the spine. Given that how can you feel that building on the weakest axis would equate to a lower failure rate? I could mention the SN curves of composites and the fact that many here have conventionally wrapped glass blanks that have withstood these torsional forces for several decades.

Or to put it in another light....if one were to look at a load calulation for a cantilever beam end loaded....are you suggesting the torsional stress in the beam would be different if one rotated an I-beam 90 degress (so it went from strongest to weakest axis)?

Russ in Hollywood, FL.

Joe,

I did not say it was not stressed, I said the only way not to stress a rod blank is to not bend it. Blanks are designed to withstand stress within the parameters of what they are intended to do. Building on the spine does not reduce nor eliminate torsional force. Any rod with the guides located on top of the rod will attempt to twist.

But it matters not if a rod blank wants to twist - if it does not twist, then no damage is done. You cannot eliminate twist by spine orientation, only by guide orientation. This is not theory, it is fact. If spine orientation could be utilized to eliminate rod twist, then the folks who make gimbals might as well stop making them. Building on the spine simply does not eliminate nor reduce rod twist therefore it does not reduce stress on the blank.

If the test on rod failure, over 200 blanks were broken and analyzed. Out of the entire number broken by overload failures, not a single one showed any evidence of failure due to torsional stress. Torsion did not cause them to fail.

The idea that rods built on the spine are somehow more durable or less prone to failure is false on several counts, not the least of which concerns the fact that fishing rods cannot be fished on a single axis, which pretty much renders the spine theory mute.

Any time you flex on a rod on an axis that appears to offer greater resistance, you are compressing a greater amount of material. This does not equate to a rod that is more likely to fail, but rather one that is less likely to fail (on that axis). It offers greater resistance precisely because it is stronger in that particular orientation.

.............

I have built so far about 5 or more light rods from a 2wt fly rod into a spinning rod, to a med light, I never built on the spine just on the straightest axis, and I know like 2 of them the lighter ones I just built them without even checking the spine or the straightest axis, and they are just really nice to fish with. Just though I would out this in here, have a good one!

Two years ago I went to the Gary Loomis seminar at the ICRBE. He said he did not recommend building on the spine. He said what he told people to do is building on the curve, with the curve up so the weight of the guides would make the rod straight. I would have to think that if there was any advantage to building on the spine that Gary Loomis would know about it and use it.

Hi everyone thanks for all the info but it doesn't answer the original question if a rod has 2 spines that seem to be 180° apart should I build on one of them or 90° off.

Russell Brunt Wrote:
-------------------------------------------------------

> You granted that the tension from the line would
> always be stronger than any forces from not
> building on the spine. Given that how can you
> feel that building on the weakest axis would
> equate to a lower failure rate? I could mention
> the SN curves of composites and the fact that many
> here have conventionally wrapped glass blanks that
> have withstood these torsional forces for several
> decades.
>
> Or to put it in another light....if one were to
> look at a load calulation for a cantilever beam
> end loaded....are you suggesting the torsional
> stress in the beam would be different if one
> rotated an I-beam 90 degress (so it went from
> strongest to weakest axis)?

Russ,

If your beam is not uniform, then yes, I would expect the torsional stress to be different on different axes, and that the torsional stress would depend on the irregularities. I don't doubt that a great many blanks can withstand the torsional stress for a great many years, but it is a game of statistics, and you can't always predict when a failure will happen.

Joe

If the rod doesn't twist, then torsional forces aren't harming it. The whole issue of rod spine is a non issue.

...........

Paul,

It doesn't matter. There is no "should" or "should not." Why don't you mock up the handle, tape on guides and then go out and cast, pull, etc., a few times on various axis and then build on what you like the best. Most likely, you won't be able to tell any difference.

.............

Ok thanks will do that.

Tom Kirkman Wrote:
-------------------------------------------------------
> There is no torsional stress on a rod if does not
> twist. Therefore, building on the spine does not
> reduce stress - twist is a matter of where you
> place the guides not spine orientation.
>
> ..........


This is what you said that triggered my response. I agree that there is no torsional stress if the rod does not twist. The phrase building on the spine does not reduce stress is the torsional equivalent of saying that there are no forces acting on a person standing on the surface of the Earth. The amount of torsional stress must go up if you bend the blank on an axis other than its preferred bending axis. I'm not saying that the rod will magically flip around due to the spine orientation, only that if one wants to carefully consider the stresses on their rod that the spine does play a small roll. It may be splitting hairs, as the torque applied at the guides is going to be enough to overcome the torque from spine orientation. In my mind, if one wants to give the torsional stress on the blank the same attention that we give to the shear stress of loading the blank, the best you can do is to build on the spine as a spinning rod or a spiral wrap.

I wouldn't expect a one time load exhibit evidence of torsional stress. I would expect it to show up, if at all, after the load being applied many times.

I'm also not saying that I would expect a rod flexed on a stiffer axis is more likely to fail due to compression. My only concerns are in the long term use of rods wrapped conventionally. If there is a higher failure rate associated with casting rod and the torsional stress from having their tips twisted 180 degrees, then building off of the spine will not do anything to help the situation, and would slightly increase the failure rate.

Personally, I tend to build on the straightest axis, and the spine in the back of my mind.

Joe



Edited 1 time(s). Last edit at 12/09/2012 06:35PM by Joe Vanfossen.

This whole spine issue first raised it's ugly head in an issure of the "Original" Rodcrafters Journal. Back then people were calling it the "SPLINE". I never have been able to figure out where they got that term. I started making arrows before I made fishing rods and the spine was essential in making an arrow that flew true. The spine of the arrow was either against or opposite the bow upright. Anywhere else and the arrow would not fly true. When I first started making rods, I spined them the same as arrow shafts, but I always tried to aligne the spine with the rod being in the straightest position. When making a casting rod I put the guides on top of the curve, and on spinning or fly rods on the bottom of the predonminant curve. This usually followed the spine of the rod.

I have never figured out how the spine affected fishing, especially when the fish is running right or left and not straight down. Should you rotate the rod in your hands so the spine is always perpendicular to the fish? If not, the spine is 90 degrees opposite the fish. I think spine may be able to give a more accurate cast and possibly more distance in the cast, but as far as fish fighting, I have no concrete evidence that it matters one whit!!

That's what i like about rodbuilding, nothings etched in stone. Just do what you want. This whole spine thing is just one confusing area. I'm finding out the they used to say one guide per foot plus the tip top, then changed to one per foot plus one, then the tip top. Now the lastest is see is the fewer guides you use the better. It justs comes down to do whatever you want and make it look good. Way too many variables for the new comer to try to grasp.

Jack, the Microwave guides are reccomended at 9 guides and tip for a 7 foot rod!!! Not fewer is better`!!