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Old 07-16-10, 11:16 AM   #1
HarveysMinnow
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Default A rudimentary method for measuring rod stiffness

As we can surmise from the prevailing opinions in a recent thread on rod fatigue (or the lack of it), our fishing rods should last a lifetime, as long as we protect them from various forms of abuse. Also, it was asserted by several members that ‘rod stiffness’ or ‘flex resistance’ is not likely to change noticably over years of use.

If these opinions hold true, why bother to measure anything? Well, perhaps there’s a couple other facets of this topic for which some numerical values might be of some benefit to us:

Let’s say we wanted to compare the flexibility or stiffness of two or more of our existing rods. We could do this ‘by feel’ or ‘by sight’ perhaps, but other than subsequently saying one rod is stiffer than the other, we would not have much to hang our hats on. For some folks, that’s enough – they don’t care about any numbers – they just want to catch Bass, and I can’t fault them one bit for that. Others sometimes want to know more, and for those of us who fit that category, or those who just like to tinker with things, it’s sometimes a challenge to figure a way to obtain a number that will mean something. (If nothing else, it’s something to do when it’s just too danged hot to fish.)

Another instance where a ‘flex number’ might be helpful is when we go out to purchase a new rod. Maybe we would like it to be as close as possible to the same stiffness of one of our existing rods. Or maybe we would like to see if comparable rods of different brands are similar in stiffness. Whatever the case, some of us just like to derive our own numbers.

Fishing scales – the type with a digital readout – contain a cheap but functional version of a strain gauge. Not only can these scales weigh Bass, they can also be used to set reel drags to a certain percentage of the line breaking strength. Along these same lines, they could be used to obtain a relative value for the flex resistance of a fishing rod. [When I say ‘relative value’, I just mean that the readings we make don’t relate directly to any standard. We have no way of knowing whether the strain gauge in one unit is calibrated the same as in another unit. Hopefully, they would be close, but unless someone wanted to purchase several of them and test their uniformity, we just won’t know for sure.] This means that one person’s readings could vary from another’s, even on the same brand and model of rod.

In order to make a measurement on a particular rod, we will need some way to secure the handle end, so that we can pull the rod tip across an arc that approximates the range of flex that the rod may experience when a fish is hooked. We can decide on a suitable degree of bending by visual experimentation, but first let’s look at the rod holder.

As you can see in the photo at the end, my rod holder was constructed so that it can be anchored to one of the legs of my workbench, using a sturdy woodworking clamp. The base of the rod is inserted into the 1-1/8 “ hole. The rod also rests against an adjustable block, which can be positioned in the general area of the reel mount (with the reel removed). The resting point where the rod fits against this block becomes the lower end of the flex curve when the rod tip is pulled horizontally. For the setup in the photo, I would pull the rod tip to the right.

To make the actual measurement, you will need one of the digital fish scales mentioned above. Cabelas sells one made by Rapala which has a 0 – 15 lb range and reads in pounds and ounces. Also available, from a company called “Micromark”, is a similar but more sensitive device designed to measure drawbar pull of model railroad locomotives. It’s range is 0 – 176 ounces (11 lb) and it reads to the nearest tenth of an ounce. Just hook your measurement unit onto the rod tip and pull against the block to some arbitrary point where the rod tip is horizontal (or to whatever point you believe is appropriate). You may want to mark this spot, if you want to compare your readings for two or more rods of the same length. (Also, if you are into statistics, you may choose to take several separate readings on the same rod and average them.) Whatever the case, it’s important to pull the rod(s) tips to the same point for each reading, otherwise the numbers will be meaningless.

Some typical values:

Since most of my rods are of the ultralight to medium action variety, I opted for the more sensitive unit mentioned above. Consequently, my values are in ounces, and they are the average of three reps for each rod.

Shakespeare micro-graphite 5’ UL spinner 13.7 oz

Shimano VTS 5.5’ L spinner 13.3 oz

Shimano Sojourne 60M2 6.0’ M spinner 25.1 oz

Diawa Strikeforce (no1) 6.0’ M spinner 21.9 oz
(Two identical rods)
Diawa Strikeforce (no2) 6.0’ M spinner 19.5 oz

Gander Mtn X-factor 6.5’ BC 38.4oz

Field & Stream (IM-6) 6.5” BC 39.6 oz


Now that I’ve done all this, I’m not sure what I’ve learned, if anything. I guess I expected the two bait caster rods to yield higher numbers than they did, based on the way they feel. Other than that, no major surprises from my point of view. I believe the two Diawa rods are virtually the same, within the limits of experimental error. So, I invite comments, critiques, questions, and opinions from you gentlemen. I realize this is a long and involved posting, so I thank you for your time & indulgence.


Safety Considerations: If you decide to try this at home, be careful you don’t whack yourself or someone else in the face by releasing the rod tip abruptly. A flexed fishing rod can hold considerable stored energy, so return the rod to its unflexed vertical position before unhooking the measuring device.

Disclaimer: (This forum member assumes no responsibility for damage to equipment or personal injuries incurred while following this procedure.)

On a lighter note and in view of remarks made in other threads, I fully suspect that someone will decide to wise off about this. So allow me re-emphasize that we’re talking fishing rods here, and that attempting to use this method to measure stiffness of your personal anatomy is not recommended.


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Old 07-16-10, 11:38 AM   #2
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Harvey, I love your approach, and over-analytical nature. (Of course, the guys here knew I would).

I have a couple of comments and suggestions about your method.

First...you have to make sure not to assume a linear strain. On some XF (extra fast) action rods, the rod may actually perform like two different rods. In other words, the rod tip may very well approach horizontal under load, and then the rest of the rod may start to flex. The rod may have a lot more give to it after the rod tip initially reaches horizontal. Just something to keep in mind when trying to interpret your results.

Second...I have envisioned this setup many times, and I came to the conclusion that in order to be 100% accurate, the rod should be mounted horizontally, and varying weights hung from the tip. Coming from vertical, there is just too much opportunity to impart a lateral force on the tip. Ideally, when the tip is at 90 degrees to the butt, the force applied should be 100% parallel with the tip. I'm not sure you can get that the way you are currently set up without a lot of trial and error.

Additionally, there is always the rod's spine to consider. there is no reason to assume the builder gets the spine perfectly oriented. So you have two schools of thought on holding the butt end. Grip it in some sort of vice, or put it in something that allows it free rotation. The former will test the rod "as-built", while the latter will give a bit better evaluation of the blank's potential, negating some of the effects of individual craftsmanship of the builder.

Regardless, keep up the good work! Enjoyed the post!
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Old 07-16-10, 11:53 AM   #3
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Harvey, great thread and great idea. When it comes to fishing rods and rating power and action, there is no universal measurement.

There are a couple of ways to put numbers to the power a fishing rod has. One is the Common Cents System. The other is to use the RoD, or Rate of Deflection.

You'll have to do some reading on the Common Cents System cause I'm not to familiar with it.

If you read any of the rod reviews on TackleTour, then there's no doubt you've at least heard of RoD What they do is set the rod up at a 30 degree angle. Then they progressively add to the weight hanging from the rod and measure how far the tip has moved from the original position. Then they graph it. Mostly it is a comparison between rods rather than an actual value put to the power of the rod. But at least it is a consistent and empirical way of doing it.

Here is an example of a RoD Chart from TT.


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Old 07-16-10, 11:59 AM   #4
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Worthwhile responses from both you guys...thanks.

I did say this was 'rudimentary', right ? I'm not sure I could do much better here in my home shop, but at least it provides food for thought.

Obviously I could stand to do some more reading.


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Old 07-16-10, 12:00 PM   #5
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I also like the read and would like to pass on an article that Ive been reading recently on the matter,among others

http://www.common-cents.info/

Very good read.

I see Anthony already brought it up.

Also I believe NF is correct with mounting the rod horizonally...I do this for strength and static testing...Usually at a 45 degrees for the static guide placement and recently about 90 degress for strength testing.....which is still something Im experimenting with as I learn
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Old 07-16-10, 02:43 PM   #6
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Old 07-16-10, 02:59 PM   #7
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Mounting the rod horizontally would certainly solve one of my logistic problems: My shop has a 6'9" dropped ceiling, which means I cannot test any of my flyrods vertically.

Thanks for the reading reference to the Common Cents System. My problem is that I'd rather tinker around than read, but it's still worth knowing about.


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Old 07-16-10, 04:11 PM   #8
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Harv...I'm getting that you're taking your readings from direct hookup at the rod tip. Wouldn't you really want to incorporate the guides, through using line, which will give you a more accurate reading of the entire rod flex? Not sure of the merit, just throwing it out there.
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Old 07-16-10, 04:15 PM   #9
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Quote:
Originally Posted by HarveysMinnow View Post
Mounting the rod horizontally would certainly solve one of my logistic problems: My shop has a 6'9" dropped ceiling, which means I cannot test any of my flyrods vertically.
Oh man, I wouldn't be able to test more than half of my bass rods with a 6'9" ceiling, lol.

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Old 07-16-10, 04:17 PM   #10
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Quote:
Originally Posted by BigBassin144 View Post
Oh man, I wouldn't be able to test more than half of my bass rods with a 6'9" ceiling, lol.

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Old 07-16-10, 04:30 PM   #11
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When i static test rods I put them in a jig at about 45º. I tie a line from the tip to something i can add weight to. This allows me to get a consistent pull and I can add or subtract weight as needed. Not sure if this applies to your experiment but it might add a level of consistency.
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Old 07-16-10, 05:42 PM   #12
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Quote:
Originally Posted by geezer1 View Post
Harv...I'm getting that you're taking your readings from direct hookup at the rod tip. Wouldn't you really want to incorporate the guides, through using line, which will give you a more accurate reading of the entire rod flex? Not sure of the merit, just throwing it out there.

+1 for the Geezer!! ABsolutely interesting theory and fairly well thought out, but for it to truly mean something useful, I have to agree with Geezer on this one.
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Old 07-16-10, 08:00 PM   #13
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Quote:
Originally Posted by geezer1 View Post
Harv...I'm getting that you're taking your readings from direct hookup at the rod tip. Wouldn't you really want to incorporate the guides, through using line, which will give you a more accurate reading of the entire rod flex? Not sure of the merit, just throwing it out there.
Quote:
Originally Posted by Bob Smith View Post
+1 for the Geezer!! ABsolutely interesting theory and fairly well thought out, but for it to truly mean something useful, I have to agree with Geezer on this one.
Geezer brings up a good point. You have to consider what the effect of the guides on the rod are. They can make a rod slightly stiffer...very slightly. However, the placement of the guides can affect rod action quite a bit.

However, I think the point of the OP was to measure the rod's stiffness (power). And I believe he is measuring a rod with the guides already attached. In that respect, the question of line running through the guides or merely tied to the tip (with empty guides elsewhere) will not change anything. This is because he is measuring the rod statically. If he were measuring how fast the rod loaded (I mean time-wise, not referring to action), maybe the friction of the line through the guides it could conceivably make a difference there.

Still, I am one for re-creating real world conditions during testing whenever at all possible. Sometimes there are just stupid things you never could have forseen that have profound impacts on the results. Perhaps he could also put a reel on the rod and string it up for a 100% realistic test!
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Old 07-16-10, 08:25 PM   #14
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You know, I might be wrong about the guides not making a difference. I'm scribbling on paper right now and trying to figure it out.

***EDIT***

Nope, I'm sure of it now. No difference. I finally had to do a free body diagram of the string attached to the weight/scale to figure it out.
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Old 07-16-10, 09:50 PM   #15
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Quote:
Originally Posted by nofearengineer View Post
You know, I might be wrong about the guides not making a difference. I'm scribbling on paper right now and trying to figure it out.

***EDIT***

Nope, I'm sure of it now. No difference. I finally had to do a free body diagram of the string attached to the weight/scale to figure it out.
I'm thinking that's also the conclusion that Dr. Whoever came to in his treatise on the Common Cents System for evaluating fly rods.

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Old 07-17-10, 06:58 PM   #16
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I prefer to use the Ron Jeremy Scale
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