Fly rod guide selection

[Merlin]

Hi Gordy

There is a difficulty in measuring the stiffness at right angles which is due to the spine of the blank. I did that for a tip section of one of my rods and there was 7% stiffness difference in between planes. This difference results from both spine and guides effects, which where placed in the NBP.

So spine can have an effect equivalent to guides in amplitude, and more than that likely (I measured sets of sections with up to 21% difference in stiffness).

If one looks after pure guides effect it is necessary to locate the spine of the blank and place the blank in exactly the same position with and without guides.

Frequency measurements appears to be more difficult since you can get a whirl. In that case the rod vibrates along two different combined frequencies. Some kind of nightmare, you see.

Merlin

[Paul Arden]

Hi Merlin,

I think that whirl is pretty common actually but also because we rarely bend the rod on a single plane. That’s actually a pretty significant difference with regards spine. I know it must be there because we can feel it. However I thought that the ring alignment created its own “spine”.

Lasse, that’s a lot of work. Did you epoxy between the tests or simply strip and rewhip?

Cheers, Paul

[gordonjudd]

This difference results from both spine and guides effects, which where placed in the NBP.

Daniel,
Did you fine the neutral bending plane (NPB) by placing the tip in a spine finder so it would roll to the NPB when the tip was deflected to some point. Then the guides were placed on the inside (bottom) of that bending curve as noted in Dave Tutleman's article on golf shafts?

The shaft is not only a spring; more specifically, it is a flexible beam. Note that I didn't say, "Perfectly symmetrical flexible beam." We're talking about spine and FLO here, so we are exploring what happens when the cross-section of the beam is not symmetrical. That leads us to a few more facts that engineers know about flexible beams, even asymmetrical beams:

If you deflect the shaft and measure the spring constant (the stiffness), then deflect it in exactly the opposite direction (that is, exactly 180º away), you will get the same spring constant. It is equally stiff in both directions.
If the cross-section of the beam is not perfectly symmetrical, then the beam may have a strong plane (the direction of highest spring constant) and a weak plane (the direction of lowest spring constant). Clubmakers refer to the strong plane as the spine and the weak plane as the Natural Bending Position (NBP) -- or at least they should if they are using the right measuring instruments.

Thus his Nomenclature gives the spine and the neutral bend planes as
'Spine' Strong plane Direction of highest spring constant
'NBP' Weak Plane Direction of lowest spring constant

Thus finding the NBP would mean the spine (strong plane) was 90 degrees away from the NBP.

From Tutleman's golf shaft conclusions I am assuming a better way to align guides would be to align the guides along the flat line oscillation (FLO) axis as he describes in this article.

I would imagine that the angle difference given with the NBP found in a spine finder and the FLO axis would give an indication of how much different the spring constant was in the two directions but I could not figure out how to calculate it.

Gordy

[Torsten]

Hi Daniel,

have you simulated that? I'd love to try that with an FEA tool, what were your design parameters for this comparison?

Thanks,
Torsten

Hi Paul

I tried a more accurate approach with recoils single foot and snake guides (not the light versions). I confirm a 1% difference in between guides systems for the stiffness of a tip section of a 905, the snake version being the stiffer.

If I compare a blank tip to a section with guides, I find that guides increase the stiffness of the tip section by 2.5% to 3.5%. You should be able to find that if you measure a tip only. For a full rod it should be less.

Making a CCS type of test on the tip section shows a very small difference in mass at tip level in between the two guides systems: 1 grams among a total of 80 to get the 33% deflection.

Merlin

[Merlin]

Gordy

I'm using the same nomenclature than Dave.

Identifying FLO is necessary if the rod section has a whirling behavior under vibration tests. This was not the case with the tip section I used (I know the design of this discountinued rod). I checked the NBP with a hand rolling test. Here is the scheme of the test and the outcome (red arrows show the location of guides):

guide position.JPG (32.6 KiB) Viewed 2251 times

If I use the configuration on the right hand side, the stiffening of guides is nil and I just can see the effect of the bending assymetry. Furthermore it was stiffer than the normal position (left hand side), and consequently I cannot deduct the stiffening effect of the guides.
If by chance guides had been positionned in the stiff plane (90 degrees from this one), it would have been risky to conclude that the stiffening was only due to guides. The difference would have cumulated assymetry and guides stiffening. I just got that for the mid section of that rod and the stiffness was 21% higher in that case.

Merlin

[Merlin]

Hi Torsten

I use a 31 element FEA file of my own (checked against pro software). I define the length of elements holding guides using their footprint. There is no problem to evaluate the stiffness due to guide foot, but it is not the same story for the loop of the snake guide. I am using a single spring coil to simulate that. My best guess is that the loop stiffness is about 14% the one of a single straight wire of same diameter, same overall length.

For the calculation I made, there are four guides and a tip top. I then defined 5 specific elements and had to adapt the others to get the same description of the blank (I could match 99% of blank stiffness). Adding guide sets (single foot, snakes), increases the blank stiffness by a few percent (4% to 5%). The single foot set of guides appears to be the stiffer by 1%.

I would say that both sets are equivalent and increase tip stiffness by a little. This difference is likely smaller for a tip mid section, negligible for a mid butt section, and nil for a butt section. For a full rod that could be pretty hard to see if you carefully position the blank sections with and without guides, otherwise the bending assymetry will prevail.

Merlin

[Paul Arden]

So I have a couple of questions!

We have our spine which is the carbon overlap. Are the two planes of bending always at 180 to each other or does it depend on the amount of overlap? Is it not possible that the length of overlap can cause the planes of bending to be greater or lesser than 180 degrees?

The second question is is the spine always straight or does it not curve slightly up the blank? This will no doubt depend on how the cloth is cut.

Thanks,
Paul

[Merlin]

Good questions Paul

The spine can curve (I studied that), and the two main axis can rotate consequently. Axis (and planes) are 90 degrees apart, not 180.
I have written a paper on that, maybe I should read it again and send it to you. It is a bit technical if I remember well.

Merlin

[Paul Arden]

Thanks Merlin. Another thought, I see you are measuring the stiffness of the snakes. Would not the two epoxied feet plus snake wire in between be stiffer yet again?

Cheers, Paul

[gordonjudd]

I checked the NBP with a hand rolling test.

Merlin,
In my experience it is even better to use a spine finder so that its roller bearings can roll to the neutral bending plane (NBP) since the end of a blank section may not be round and can affect the hand rolling test.

Regardless of how you find NBP with a static test I find that when you oscillate the rod along the static NBP the tip will still whir. I have often wondered why that is the case as discussed in a thread on the old board, but suspect it has to due with the differences in the shape of the static bendform of the rod as compared to its mode shape when it oscillates.

Dave Tutleman's approach to finding the flat line oscillation plane (FLO) is a good one for finding the dynamic spine axes and even provides a way to estimate the the differences in the the k spring constant value in the dynamic NBP and spine planes. He is adamant that it is important to use the FLO plane for golf shafts since the club head will still tend to twist if it is aligned on the static NBP axis. Phil can probably appreciate the difference since the initial ball flight is primarily determined by the direction of the club face.

I will do some tests and start a new thread on how to apply his approach to measuring the amount of spine in a fly rod.

As an aside I would still mount the quides on the NBP since the rod will not tend to twist in your hand when fighting a bigger fish with that alignment. The saltwater rod manufacturers are very careful to use that alignment as well since a big fish can put a lot of twist on a standup rod when fighting a Tuna.

Gordy