Failure from overload and failure from fatigue are different yet similar, at least insofar as one ultimately has an effect on the other. All materials weaken over time from a variety of factors - use cycles, environment, age, etc. Focusing on cycles let’s say you have a new rod blank that can withstand 20 pounds of load before failure. After 900,000 cycles it might only withstand 19 pounds of load before failure because each cycle has infinitesimally damaged it.

What Joe is getting at, and he’s not the first to suggest it, is that when a rod is flexed off the spine, and even though no actual twist occurs, there are torsional forces working internally to cause and/or accelerate the damage done to the rod blank during each cycle. Conversely, however, for any given load a rod will flex more deeply when flexed on the spine than when flexed off the spine, causing more damage per cycle. Want to guess which one causes the greater damage per cycle?

As I’ve said many times, however, most of these type discussions are wasted academia because the number of cycles required to cause any practical weakening or failure in a graphite rod blank, whether the rod is built on the spine or off, is of no real concern to the rod builder. We don’t and can’t cast and fish a rod on a single specific axis so to worry about the minute strength or durability differences of building on or off the spine is a waste of time.

Within the scope of what he wanted to know, I think Adam gave Paul the most practical answer in this entire thread.

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i can not believe this subject has 4 pages

some one is playing here ???

Bill - willierods.com

I thank you all for your input, I didn't know it was such a volatile subject. Oh and since it has 2 spines I am going to build it on the straightest axis which doesn't align with either spine.



Edited 1 time(s). Last edit at 12/11/2012 03:39PM by Paul Luechtefeld.

Paul,

If it managed to help you in any way, then it was worth it.

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There was a post a while back that a builder was told that if you don't build on or with the spine of the blank on a spinning rod that has the guides at the 180 the guides would tend to go - Get This ( up ward ) ya I know it sounds crazy

I could not stop laughing

Check the Search Function up above and you will find Many Many posts on this

Bill - willierods.com

Actually, Cam Clark, editor of the old Rodcrafters Journal, told me that - he said that under pressure the rod would turn until the guides spun to the top.

Over time, of course, the Rodcrafter people changed their stance on rod spine and decided it could not be used to stop rod twist.

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Tom

I read a lot of posts here

You are not going to tell me that this is possible - Are you ?????

With a fish on - How would this be possible

Bill - willierods.com

It won't happen, no.

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Bill,

Rest assured, those blanks wont flip.

Tom,

Your test with loading the rods and torsion still has me thinking a bit. I'm still curious as to the average angular displacements between the on-spine and off-spine blanks. Another useful number would be ratio of the bending load at the time of failure to the average minimum dead lift capacity. If the bending load is close to the maximum that the rod can handle, I would expect the overload failure to be the dominant mode of failure in the test.

Another question is how many full 360 degree rotations does it take to cause a torsional failure in the blanks used in the testing. Your response to Mr. Finch seems to imply that it is greater than 360 degrees, but not how much more. Do most of them fail within the 360-720 degree range, or higher? If they fail in the 360 degree to 720 degree range, then they are routinely loaded to 25% to 50% of their elastic limit. The reason I ask is that most blanks (particularly the freshwater blanks I build) are very rarely stressed anywhere near their elastic limit. Casting, retrieving and fish fighting, even though many of the blanks can withstand much more, they are typically loaded with a couple pounds or less. This puts the average loading cycles of both bending and torsion on equal footing both in the depth and number of cycles.

When discussing blank failure, you often note (and everyone should agree) that the outermost fibers in the blank are the ones that provide hoop strength (also the outermost longitudinal fibers do most of the load bearing), and that once these fibers are damaged, the rod becomes compromised. It is these outermost fibers that provide hoop strength that are the fibers that are also responsible for handling torsional stress. I would expect that once a relatively small number of these fibers fail with the rod under load that the break would proceed as an overload type of break when the rod is flexed fairly deep. Once the hoop strength begins to drop, then there is little to keep the longitudinal fibers in the resin, and the fracture should continue much like an overload.

The line of questioning is not for the purpose of being argumentative. Yes there were a couple points that I disagreed with pretty strongly, and started the discussion. It's mostly because I can't convince myself that the spine should be dismissed as easily as we dismiss it these days.

I can buy the argument that when used normally without abuse that the spine orientation doesn't matter as the blank can withstand a great number of load cycles without showing significant signs of wear, but not because the torsional stresses don't matter, but because both the longitudinal and torsional stresses are well within the blank's elastic region. Yes, I know the blank will see significantly more flex cycles closer to the elastic limit in bending stress, but with respect to wear, the average depth of cycle for torsional and bending stresses are on equal footing.

Joe

Several years ago - at one of the original ICRBE's in Charlotte as I recall Don Morton had a contraption that demonstrated that the "spine / spline" of a blank was actually different along the entire length of the blank (although there was a predominant 'soft side' when measured along the entire length). With the changes in blank design over the past few years using multiple "flags" of scrim; multi- pattern material designs of scrim and using nano-particles in the resin(s) and differing the pressures applied the discussion about spine is more irrelevant than ever before. I also doubt that in a fishing situation I (or anyone else) is going to rotate a fishing rod 360 degrees.

Ken,

The spine isn't a physical attribute of the blank - it's an effect caused by about a half dozen manufacturing anomalies. Therefore it tends to shift or spiral a bit as you flex the blank deeper and deeper. Adding guides to a blank will change the location of the "spine." So does the overlap on a multi-piece rod.

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Joe,

For any given cycle, a blank will flex more deeply on the spine than off, taking it closer to the edge of the elastic limit on each cycle. Would torsional stress when flexed off the spine do equal damage to that done when flexing it deeper? Due to the manner in which similar structures are generally orientated to offer the most strength and longevity, it's not likely to be the case. But to convince yourself you'd have to run a blank through a specified number of constant cycles to see if the blank would withstand more or less cycles before failure when flexed on or off the spine. As interesting as such an experiment would be it requires equipment that most of us don't have on hand. I suspect there is a tubing manufacturer somewhere, however, that would already have that answer.

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Tom -
Agreed.

Ken,

The new techniques in blank making are definitely for the better, and producing lighter, stronger, more durable blanks than before.

Tom,

I agree there have to be people out there with the answers to the questions I'm asking. Maybe someday we'll have an answer. The equipment needed and the time for the tests are definitely beyond the needs of the custom builder.

Joe

Joe, have any aerospace engineer friends? Maybe even someone in the golf club area could help.

Russ in Hollywood, FL.

Ken,

Oops forgot to mention, I agree a 360 degree rotation is outside of realm of reason for a fishing situation. I put the practical max at 270 degrees for when a conventional wrap twists to put the guides on the bottom, and then a fish makes a run to the side pulling the guides further around. Even then you aren't likely to make it all the way to 270.

Russ,

One or two people come to mind, but it's been a while since I've talked to them. If I get some good info, I'll share.

Joe

The comment in my previous statement about how structural components are generally oriented, was based on an earlier career which involved structural design and not once did I, nor did I see anyone else, orient a component in such a way as to put anything less than the maximum structural resistance in line with the expected or intended load. While overly simplified and certainly not exactly the same thing, a guy building a deck would be using poor design principles if he oriented his 2x6 floor joists so that the thicker cross section was horizontal rather than vertical. A poor analogy perhaps.

Another thing comes to mind about how far you can actually twist a rod blank in actual use. It would be rare to actually have a rod blank twist 180 degrees. Once the line passes below the rod blank, no further twist occurs, I think. Before I lock into that statement, however, I need to either wrap my head around it a bit more (working on a magazine deadline at the moment) or go try it.

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

From a practical point...I have seen heavy roller guide rods twist. I have never seen them twist 180 degrees. Maybe a light blank would. I suspect...unless the line became fouled on a guide......that once the fish moved in the opposite direction the tip would flip over and rotate the other way.

Totally agree that it would be beyond silly to orientate on the weakest axis. That alone was enough for me to dismiss the notion of building on the spine when it was first advanced decades ago. Interesting to note that many who once swore by it latter reversed their stance. Still it lingers on as a hottly contested idea....no doubt the sports mag writers are partly to blame.

Russ in Hollywood, FL.

Russ and Tom,

My mind went to what the worst case scenario would be, and I envisioned a guy in a fighting chair with the rod locked into place with a gimbal, and a large fish surging to the side at the boat. After thinking a little more, I'll have to play with a few rods to see if I can replicate the situation. It do think it would likely take some exceedingly rare circumstances to get the blank past 180 degrees. I may have thought a little too hard on that one. We'll see.

Joe

Another thing that strikes me, and one I never see mentioned by others, are forces when casting. I'll assume I'm not the only one that rotates a baitcaster 90 degrees when casting. I can tell you I have broken 20# test line test casting 3 ounce sinkers. At that moment the blank is under a lot of torque. Strip out 2- 3 foot of line and tie it off to an unmovable object. Then rear back on your rod, rotated 90 degrees from normal, violently enough to snap that line. That is what can happen in a cast yet nobody suggests that is capable of harming a blank. Factor in that you have a twist in one direction, followed by a return to normal, than one in the other direction. I think you are getting a good 180 degree twist here. My experiences suggest casting causes a type of stress condition more likely to exceed the elastic range than any fishing condition.

Russ in Hollywood, FL.



Edited 1 time(s). Last edit at 12/14/2012 06:18AM by Russell Brunt.

Russ,

No doubt about it, the cast and hook set are a couple times when the rod gets placed under high stresses for short amounts of time. That's what I had in mind when thinking about the average depth cycles for bending and torsional stress. It is surprising when you think about the forces required to change the momentum of an object in a short period of time. Was that 20lb. line mono or braid? The lack of stretch in the braid makes the high impulse loads more of a factor. The reasons many over line their rods in bass fishing are not so much for fighting the fish, but for abrasion resistance and to handle those high impulse loads of casting and hook setting.

I tend to worry about the hook set on my rods, as many bass fishermen have a habit of setting the hook with a fair amount slack in the line, and particularly on short line presentations where there isn't more than 20'-30' of line out. The worry here is both the angle of the rod, as it puts the rod at risk of receiving a shock load while high sticked, and the sudden stop if the hook buries into a heavy immovable object. It's also the reason we hear, well the rod broke on the cast, or it broke when I set the hook on a 1lb. fish. Once enough damage is done, it will fail on the next shock/high impulse load.

Of course, I think a lot of bass fishermen learned the hard way about the stresses involved in casting when they tried casting the new fangled Alabama Rig on their regular rods. There's no doubt that the stresses in casting can exceed the elastic limits of the blank when the lure/bait is too heavy.

I worked on casting with the rod rotated when I was learning bait casters and using old Millionaires and Garcias, but after switching to the low profile reels, I leave the reel on top. Casting with the reel rotated never felt natural to me. With at least 2 bearings supporting the spool shaft, no bushings, and the lower inertia spools, I feel the differences are minimal whether the reel is rotated or not.

Joe