Joe,

There is no "preferred bending axis." The blank doesn't prefer to bend on that axis, that's simply the axis on which it flexes under the least amount of force because it has the least amount of material on the compression side in that orientation. But it does not "prefer" to bend there, nor anywhere else. It resists bending on all axis. I've often heard builders say that a blank "wants" to bend on the spine. No it doesn't. It doesn't want to bend on any axis.

If you orient the spine up on a casting rod, it's still going to try and/or twist. The spine will neither cause nor stop that from happening. Any rod that has guides located along its topside will be inherently unstable.

On a spinning rod or any rod with a spiral wrap, you aren't reducing stress by putting the spine in any particular orientation. Such rods are inherently stable. For the most part, they face the direction from which the load is being applied so any sort of extreme twist isn't going to happen, regardless of where you orient the spine.

Assuming you could actually cast and fish a rod on a single axis (you can't and don't) then the axis that puts the most material on the compression side will withstand the greatest number of similar depth cycles before failure. Building on the spine cannot possibly create a longer lasting nor more durable rod.


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Roll the blank on a flat surface - Or just look down it If there is any bend in it make that go UP mark the top

if a casting rod mark it the same way - Spiral it Guides on top of a blank will ALWAYS want to go down ( gravity ) Spiral no twist Add weight to a spinning rod Does it want to twist No The guides are at the lowest point

Bill - willierods.com

Its only aesthetics. For me its 'Belly to the Bottom' which puts the straightest flattest axis in line with the anglers eye almost every time.

Riley Rods-Hard Core Grips to Go!-----Carbon Fiber - Composite Grip Store-----Capt Mike's Blog-----No Excuses Fishing Charters

Tom,

The blank does resist bending on all axes, and will flex into whichever shape you force it into, but the principle of minimum potential energy says that a deformed body will seek the configuration with the lowest potential energy. That means that the blank will attempt to put the side that bends easiest on the bottom. The blank does 'prefer' to bend on that axis. If it didn't, it wouldn't obey the laws of physics. If you bend it along any other axis, there is a torsional stress on the blank, regardless of whether the blank actually twists or not, because the blank will seek the configuration with lowest potential energy, but it cannot get there because you are applying a load that is forcing it into another shape.

The laws of physics are what they are, and if you apply and interpret them correctly, you will find that the spine is real, and it has some effect on the stresses of the rod blank.

To the fisherman, the spine doesn't matter, but if a rod builder wants to build a rod that minimizes the stresses on a rod, then it does matter.

At this point, we may have to agree to disagree.

Joe

Bill,

Gravity is not the reason that the guides on a conventional wrapped rod go to the bottom when under load. It's a combination of the torque applied to the rod blank by the direction and magnitude of the load on the end of the line.

Joe

Good point

Bill - willierods.com

I`m getting a little confused so I will not bring up the possibility of a blank having three spines.

Bill

whew, 3 pages of spine, spline...
the data are on the rodmaker magazine published a few years back but some still argue about spine, and some still continue to call it spline.
some builders are stubborn as goats and some dont wnat to admit they are wrong even if the data proves them otherwise- this is especially true to "old" builders, they think they've built 1,000 rods and they thought what theya re doing si right. it hasnt sunk into their brains that they';ve just been doing it wrong 1,000.



Edited 1 time(s). Last edit at 12/10/2012 01:25PM by ridge orjalesa.

Randolph, i was referring to larger type spinning guides not micro guides. I read at one site they said the more and bigger guides you use adds weight and effects the action. They said to use the least amount of guides in the smallest size after the reduction and choker guides to accomplish what you want. And that is to have the line follow the curver of the flexed blank with equal distant from the blank. Now if that's changed, it would support my last post. Thanks Jack

Bill,

The issue of multiple spines is related to the types of variations in the blank, and how they change along the length of the blank. In the case of 3 spines. You will have 3 minima in your potential energy, with each corresponding to one of the spines. However, one of them will correspond to the lowest possible potential energy, and that is what people refer to as the 'dominant spine'.

Joe

Joe,

If you want to minimize stress on the rod blank, then don't bend it. I find this whole conversation absurd. It is the resistance to bending that makes a rod blank suitable for its purpose. Putting a blank in a position where it offers less resistance isn't making it more durable nor stronger you are simply exposing it to earlier failure.

For the same depth cycle, you are actually putting more stress on the blank when you bend it on the spine than on any other axis because there is less material there to resist the load. If building on the spine resulted in less stress on the blank, it would not fail sooner than when flexed on any other axis.

We know that rods built on the spine will fail sooner when flexed on that axis that rods flexed to the same degree on any other axis. The laws of physics are indeed real, but you have to apply them correctly.

Take a heavy weight and attach it to the tip of a rod blank with the blank butt inserted into a ball bear fixture so you can rotate it freely. Spin the rod slowly 360 degrees. Now increase the weight and do it again. Keep adding weight and repeating until the rod fails. Guess what axis it will be on when failure finally occurs? If you said the spine, you'd be correct. You don't reduce stress when you flex the rod on the spine. You increase the amount of stress per amount of material directly involved.

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ridge, I had to laugh at your post! The old guys who made 1000 rods weren't doing something wrong! They were doing something right!! You don't make 1,000 rods for customers and have them turn out wrong!! How many rods have you made? Over 1,000? I doubt it. I have made over 1,000 rods and have had 2 rods break out of that number. Both were through abuse. 1 was when I made an 8' fly rod blank into a light spinning rod for trout and panfish. The guy put 20# test on his reel and a large treble hook and went snaging large grass carp and tried to horse them to shore. The other was broken when the fisherman accidentally hit an overhanging tree limb on his back cast. Over 1,000 , Many more!! and you tell me and others we were doing it wrong with only two rods broken? How many inovations, creations, ideas on improving rod building have you come up with? I am curious. Let me and everyone else know.

The point, is that there is no right nor wrong way to orient the spine. It is true beyond any doubt that when you build and flex on the spine you are working with the weakest orientation and the blank will fail under fewer cycles and less load than on any other axis, but the fact is that the difference is slight and it is impossible to cast and fish on a single axis along. Therefore it simply makes no practical difference. You cannot orient the spine either correctly or incorrectly.

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Tom, I agree. What works is what works! I just don''t like some whipersnaper saying that all the "old guys" did the same thing wrong for 1000 rods. If that was true, they would never have had 1,000 customers!!! Most of them repeat customers, or refered by the repeat customers!!!!

Tom,

In the test you outlined above, attaching a weight to the blank and slowly rotating it. For the rod to always fail with the weakest axis on the bottom, a blank built on the spine will need to complete a certain number of full revolutions to fail. The blank built off of the spine should require the same number of revolutions + or - the angle between the spine and the axis it was built on. Does the blank fail with a greater or lesser angular displacement than the blank that was built on the spine?

I will not argue that the spine is not the weakest axis in the blank. It is the axis with the lowest dead lift capacity. There is no doubt about that.

The points that I do not agree with are that a blank does not have a preferred axis to bend on, and that an untwisted rod cannot be under torsional stress.

Joe

Blanks are designed to withstand such stresses. Any axis that exhibits greater resistance to bending than another is doing so precisely because there is more material involved to withstand/resist the pressure or load being applied.

If you examine the break when a rod has failed due to overload you will find no difference in the cause and progression of the break whether the rod was built on the spine or off. The rod flexed on spine will simply fail under fewer of the same depth cycles or under less load than rods flexed off spine.

I should not say that a rod could not be under torsional stress even though it was not twisted. I should say that no damage is done unless and until it is actually twisted. It would be virtually impossible to find evidence of a torsional fracture in any blank that was not actually twisted to failure.


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Out of curiousity, how far do you have to twist a rod blank to break it? Is there any set number of degrees?

There is no set number of degrees. It would depend upon a lot of factors, including the length of the blank. What you'd find surprising is just how far you have to twist one to actually cause a failure. It would be rare that 180 degrees would do it. Some of those in our test required more than a full 360 degrees before we were able to induce a torsional failure.

If you plotted a graph showing the progression from the elastic to plastic range for torsional rotation in a rod blank, it would look a lot like the same one plotted for linear flex. You'd have a very long, shallow line through the elastic range followed by a sudden, steep line into the plastic range. There's more to it but from a practical perspective the fact remains that within the elastic range it would take millions of cycles (flexes or twists) to cause a fatigue failure.

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Hi Paul,

Just give the "customer" what they want. If they think spine is important it takes all of 10 seconds to find it before the build.

If torque under load is more important, talk to them about spiral wraps.

But failure from overload and failure from stress fatigue are not the same thing are they?