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Sloppy Rod

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Paul Arden
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Re: Sloppy Rod

#71

Post by Paul Arden » Mon May 03, 2021 7:00 pm

Hi Merlin,

You could also look at that picture and ask yourself how is it possible to break rods on snags? I’m sure that most of us have broken rods on snags. I don’t know how many I’ve broken through casting. At least 50 (but less than 100!). Some new, some old. I think modulus is very important. Tim can bend some of his rods butt to tip. I’ve seen him do it, there is even a picture on Sexyloops of him doing this in a car park in Idaho Falls. But I don’t think you can bend all fly rods butt to tip!

I think it’s a lot harder to break a softer rod than it is a stiffer rod. Same applies to non stretch mono and stretchy mono. That rod that Tim has could very well behave like one of the ones this topic is about.

Cheers, Paul
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James9118
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Re: Sloppy Rod

#72

Post by James9118 » Mon May 03, 2021 7:07 pm

Daniel,

I've just measured the broken section for you. The OD was ~8mm. Interestingly the wall thickness varied from 0.45mm to 0.65mm, I wonder if this rod had a distinct 'spine' due to its construction (or whether the 'thin' bit spirals up the blank).

I too was surprised at the failure occurring at such a low deflection. I suspect a 4 point bend test would lessen the localised pressure, however I didn't have that jigging to hand.

The problem with a 3 or 4 point test that goes to a large deflection is that the beam under test effectively starts rolling down on the supports as the centre jig drives downwards. This causes the length of the rod between the supports to lengthen and this could make it appear that some softening has occurred. This would be a false assumption. The best way to determine ovalisation is to place an array of strain gauges on the test piece, however I'm not going to go into that level of detail.

The best test is to have the rod clamped horizontally and to pull on the tip as previously suggested. I've seen plenty of film of such tests but no raw data - perhaps someone with contacts can request it?

I still think you're barking up the wrong tree with ovalisation during casting leading to a feeling of the rod softening - I think there's enough casters on here saying it doesn't happen to them - it's just that the rod is not as stiff as they'd like when it comes to putting the power in.

James

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Merlin
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Re: Sloppy Rod

#73

Post by Merlin » Tue May 04, 2021 7:24 am

Thanks for information about the sample James, my guess was not that far. The graphite case is clear for me, a rod can break with a small amount of ovalisation and without any external sign of loss in stiffness. I would like to be sure that this remains the same for glass. If we can confirm that a sample can break without signs of weakness it will definitely put the assumption of an ovalisation effect out for the sloppy rod feel. That would put the end to a myth at the same time, the story I heard when I was young about the comparison between glass and cane.

In my virtual tests the ovalisation of a glass rod makes its stiffness profile with load more linear (the rod is already on the butt action side at start). With 600 grams at tip, the ovalisation at butt end is 3.5% and decreases quickly along the shaft. The rod is tilted 45 degrees upwards in this test.
Glass rod 45deg test.JPG
Glass rod 45deg test.JPG (19.64 KiB) Viewed 234 times
If those calculations are realistic, then you get no sign of drastic change in stiffness with load, despite a significant ovalisation at hand level (which you may feel or not). What I am after is an actual test which could confirm that a glass rod never changes to the point it becomes a soft spring because of ovalisation linked to load. In my virtual example the rod remains a hard spring.

I recently read a Chinese article about a bending test of a metallic hollow tube. The tube exhibits a maximum moment value with load (increase then decrease) as its shape changes. It does not break even after the upper and lower parts get in touch under ovalisation due to bending. We are not under such conditions with a fly rod made of orthotropic material.

To me, the sluggish feel is linked to the value of torque at the hand level. I aim at eliminating the ovalisation question, the fact that a rod is rather soft should be the single reason allowing to explain the phenomenon.

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

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Re: Sloppy Rod

#74

Post by sms » Tue May 04, 2021 2:59 pm

James, I think there might be a problem with 3 or 4 point bending test that is trying to compress the blank at the point contact.

We would need one end supported like the handle supports the blank without creating high stress concentration. And we would need to pull from the other end in 90 degree angle for example. Log and/or plot the force and distance.
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Re: Sloppy Rod

#75

Post by James9118 » Tue May 04, 2021 3:41 pm

Hi Sakari,

Yes, however I was wanting the blank to compress as I was looking for a softening mechanism that could possibly be associated with ovalisation, from the results I obviously did not record any softening. I found it interesting that after the initial break (at ~100N) the beam actually stiffened up to the point where it 'creased' and folded. Lasse is asking to see if data is available from the Echo rod tests.

Incidentally the wall thickness measurements surprised me - 0.45mm to 0.65mm seems a very big range to me, enough to be obvious by eye.

James

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Re: Sloppy Rod

#76

Post by sms » Tue May 04, 2021 5:04 pm

For ovalization I would try to make the contact area larger so that it would not localky crush the blank surface - if that is where it broke from.
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Merlin
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Re: Sloppy Rod

#77

Post by Merlin » Tue May 04, 2021 6:56 pm

What I am after is an actual test which could confirm that a glass rod never changes to the point it becomes a soft spring because of ovalisation linked to load. In my virtual example the rod remains a hard spring.
That’s what I said yesterday. Now skip the words “because of ovalisation linked to load” and ask yourself if some rods could exhibit a soft spring behavior in some conditions which could be met at the end of a cast.
And the answer is:
soft hard example.JPG
soft hard example.JPG (32.74 KiB) Viewed 159 times
I shall elaborate on that later but you can imagine that there is an input field which can cross the “soft zone” for some time. Instead of an increased resistance the rod gives up and bends more until it finally recovers.

Surprising isn’t it? Fanciful physics? Just adequate conditions and a slow butt action glass rod of simple taper.

That involves the design of the rod. The softness is due to the upper sections which are too weak for the power used by the caster. One has to wait to be “facing the butt resistance” to come back to a responsive rod.

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

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Re: Sloppy Rod

#78

Post by James9118 » Tue May 04, 2021 7:49 pm

Merlin wrote:
Tue May 04, 2021 6:56 pm

Surprising isn’t it? Fanciful physics? Just adequate conditions and a slow butt action glass rod of simple taper.
Daniel,

In your chart above what is the percentage difference between your ovalisation model and non-ovalisation model? Is this difference enough to cause the caster to determine the rod has become 'sloppy'? I'd also suggest there is no sudden discontinuity in the stiffness of the rod that relates to the phenomenon being discussed, your own model suggests there may be a marginal softening which would be barely noticed by the caster. I can carry 85ft + of a MED#5 on a rod rated #5 and I can do the same on a rod rated #10, I don't regard the #5 rod to be sloppy.

Physics is always fanciful if it doesn't reflect real life.

James.

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Paul Arden
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Re: Sloppy Rod

#79

Post by Paul Arden » Tue May 04, 2021 8:55 pm

For me at least, it would be completely impossible to tell the difference. I know that there has been measurements showing (almost) constant force/acceleration being applied during the cast, but I don’t think this applies to long distance casting. The moment when the rod feels “soft” for me is when I spike the force or “hit it”, ie around or after MCL. If it happened by applying constant acceleration then it should be possible to notice an actual softening, but that’s not what’s going on when it occurs (at least for me). Rather it’s during the dramatic step up in force when the results are unexpected.

Cheers, Paul
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Re: Sloppy Rod

#80

Post by Merlin » Wed May 05, 2021 8:45 am

When I experienced the phenomenon, there was no competition casting, just a longer than usual for fishing, it was just like if the rod was saying, sorry, too much for me, and then the cast failed. I never met that with a graphite rod.

Three assuptions:
* the ovalisation myth: I read that glass rods could ovalised, it could be that
* I failed to cast the rod properly: likely since I'm not more than an average caster.
* there is something wrong with the rod, too soft maybe but I do not really know.

One can chose not to investigate.

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

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