I build my rods using belly down alignment - not a spine tradition follower.

I am building a heavy weight fly rod and am only concerned about excessive blank loading to the point of failure.

The following two pieces of advice had been sent by Stephen Pratt and Tom Kirkman.

Stephen Pratt: Place the thicker part of the wall section on the inside of the curve. The more material you have on the compressive side of the blank, the better. The compressive side is always the side that will fail in loading.

Tom: Stephen also is right about which side of the blank fails under normal "load to failure" tests. All linear graphite construction blanks will fail first, on the compression side, which is the bottom of the rod blank. If you put the thickest side here, you should get a tad more strength or loading ability out of the blank.

How do you determine which side of a straight blank has the thicker wall?

This post has been edited to remove all question of spine.



Edited 4 time(s). Last edit at 03/22/2007 06:02PM by Bill Stevens.

Bill,
When you look up the definition of spine in the dictionary you conclude that it is the stiffest plane. But as you know, what we rod builders have come to think of as the spine is the axis that the blank will naturally want to rotate to when deflected or the softest or least stiff axis. Several things affect the spine but the material will tend not be the thickest on the softest axis it will tend to be the thickest on the stiffest axis. However, having said that with most blanks where the material is thickest actually rotates up the blank because of the way that the material is wrapped, where it overlaps, on the mandrel when the blank is being built.
As Stephan and Tom point out carbon fiber has a little more strength under tension than under compression so when a rod fails due to being over stressed it would tend to rupture first on the under side of the rod, the axis that was under compression. The rod will also tend to rupture or break where the stress and strain are the highest which can be anywhere on the blank depending upon how the blank is being deflected and the outer most layers of fiber have the largest load on them so they tend to rupture first. All of this says to me that it is virtually impossible to build the rod so that the material will be the thickest on the under side of the rod, where the outer most fibers are aligned straight up the rod and where the stress and strain will be the highest.

Bill,

Another misconception is that if the spine is on top that you have the stiffest axis working against the fish. This is not necessarily so because the opposite of the spine is not the stiffest axis. Rarely do you find a blank that has the softest and stiffess axii 180 degrees opposite each other.

And Emory is certainly correct about the difficulty in getting the "thickest side" of the blank on the bottom of the rod. Although we talk about linear construction, the very fact that we're dealing with a tapered shaft means that many of those fibers won't be perfectly linear so the thickest side isn't really a particular axis at all - it may encompass an general area of some width along the rod blank and one that isn't perfectly straight either.

Generally, the "thickest side" (and remember this a swath moreso than a single axis) will fall in such a way so that when you have the stiffest axis positioned so that the fish is pulling against it (straight down) you will by default have the maximum amount of fibers on the bottom of the rod.

Honestly though, I doubt you're going to see more than a tad bit of difference.

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

Bill,
If you look into the butt end of the rod with some magnification you will see a place where the plys of the blank overlap producing a slight rise. That little rise you see will be the spine of the blank. This is the side the guides go on. That locates the thickest part of the blank down. For your type application this is what you want. It will place the thickest portion of the blank under the greatest compression load. This is how Terry and I do our big game fly rods. A word of note this overlap is only about .003 to .005 in thickness but it's present; on some blanks it's really pronounced on others it's hard to see but it's there.
Michael

The rod blank spine is not a physical thing - it is an effect caused by about 6 or 7 manufacturing anomolies. You won't be able to see it although you can feel it.

The final overlap of the pattern flag can be seen and certainly contributes, but it is not the spine. Nor does that overlap travel along a straight axis.

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

Here we are again,,,,,,,,,,,,,,, with a spine,,,,,,, that has nothing to do with the fish ,,,, only everybody wants to know where it is,,, even tho it has nothing to do with anything in the building of the rod, or fighting the fish !

So said last weeks thread.. amazing that this "spine" thing keeps creeping up.. and even more amazing is what some people think a spine is or what some call a spine.

<*)))><

Yes it is amazing but old myths die hard. The fact is, flexing a blank by hand has nothing to do with, nor does it approximate in any way, what happens when you load the rod by having a fish on the end of your line.

Best bet is to find the straightest axis, put the belly down and build it that way, totally ignoring the spine. This puts the maximum amount of fibers on the bottom of the rod. Generally, the straightest axis, positioned concave, will also be the stiffest axis and have the most fibers on the compression side of the blank.

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Will the typical bend type spine test tell me anything at all? If so which side of the curve, inside or outside, should be placed on the rods bottom? I can not visually detect anything inside the butt - hunting a magnifying glass - This is a one piece 8' 4" CTS 16/18 wt fly blank. If it does fail the failure point will be a long way from the butt.

Looking at the butt of the rod for where the prepreg overlaps and results in the material being the thickest will not tell you much because this thick area will not run straight up the blank. It will tend to rotate up the blank. If you look closely at most blanks that just have clear coat on them you will be able to find a fine darker line that spirals up the blank. That is the edge of the prepreg where outer most layer is over lapping the previous layer. Also any curvature in the blank will also tend to contribute to the effect we call the spine.
I agree with Tom about ignoring the spine and where to place the guides.

Bill,

Flexing the blank by hand will tell you what happens when you bend it by hand. It will not tell you anything about what happens when a fish loads the rod via a line running through guides which are attached to the rod.

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"Best bet is to find the straightest axis, put the belly down and build it that way, totally ignoring the spine."

ok, i'm pretty much done with spine as it relates to graphite, but what about bamboo, a 6 strip blank. if there's a curve to the assembled SPLINES and the spine was checked by the maker and the specific spline was marked, directing me where he felt the guides should rest but there's that little curve, does one follow the maker's direction for placement of guides with a slight bend to the side, or can one rotate the section so, for instance, the slight bend now points up? bamboo being a completely different material, au natural, is there any possible resulting effect one should be aware of?

obviously, one should send the blank back to the maker, but just for discussion's sake... :-)

eric
fresno, ca.

For discussion sake, the spine has the same "bounce" on a bamboo rod as it does on a graphite rod, I suggest you feel for the spine yourself, (checking the maker so to speak) With regards to the "slight bend" that may be a "set" which bamboo is prone to take.
You can straighten the set with heat,,,, I suggest the stream of steam from a tea kettle. Gently putting pressure on the section,,, opposite the bend,, allow to cool, look and see what you have, repeat as often as necessary to have a straight section, it is wise also to work from the ferrule out to the tip section.
There are other makers that like to use a heat gun, iron, etc... I prefer the steam.

There is another school of thought that some makers adhere to and that is to place the guides on the next flat off the spine, and to the side to which the fisherman would be holding the rod while playing a fish.

Any other questions you can email me at : mrparramoure@yahoo.com


<*)))><

Not that you asked, but you can't straighten a graphite blank in that same manner. I'm sure you know that. The effective spine is not the curve of the blank, but an effect that causes the blank to attempt to roll to a particular orientation when flexed by hand. But again, flexing by hand does not approximate what happens when the rod is flexed by a fish attached to a line running through line guides attached to the rod.

The reasons for building on a particular axis or "spline" of a bamboo rod, or a particular axis of a wooden rod, is a bit different than doing so on a graphite rod. Much of it has to do with the set the rod may take in the future. Graphite isn't likely to take a set from being repeatedly or deeply flexed.

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

I don't beleive Eric was inquiring regarding a graphite blank but rather a bamboo blank.

That's why I said that he hadn't asked about graphite and that he probably knew you couldn't straighten one with heat anyway.


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

I can't visualize spining a bamboo blank. In my way of thinking, each of the 6 sections would have to be spined individually. After each section is shaped and glued up there wouldn't be any spine. Unless by chance each piece was properly oriented for spine prior to shaping and glue up. If not , then the spine of each piece making up the section of blank could possibly counteract each other. Therefore it wouldn't have any spine. ( does that make any sense ?) . Or is my vision completely wrong.

Yes, a built up bamboo blank still exhibits a spine effect because you are not going to have exactly the same make up in each individual spline (section) and you will have at least one axis that is softer than the rest. Again, it is an effect caused by a combination of various things. However, on any rod where you stand to have the rod take a set in the direction of deep or repeated flexing, you need to try and counteract that by how you orient the curvature or stiff axis.

Graphite rods are not prone to take a set so the reason for orienting the stiffest axis where we've discussed isn't for the purpose of keeping the rod from taking a set.

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

Take my word for it, bamboo section have a spine,,, I have run across a couple where you really couldn't detect a distinct spine, but usually it is the same as with a graphite rod. It would be very hard to try to spine each segment of the hex, since it is a triangle,, but I suppose it is possible.. but with the glue up of the section, you really kind of make one whole section.

Node placement is more of a concern with bamboo with regards to failure. And there are at least 3 "favorite" separate node spacing systems. And each maker has his own favorite. Some are so fearful of failures that they use strips from 3 separate culms to make up a section. With the thinking that if one culm should have a weak area, the other 2 culms would take up the slack, assuming of course the other 2 are free from defect.

It's a crap shoot really, cause you don't "x-ray" sections and look for damaged power fibers. However I have seen x-rays where a dentist ( who happens to enjoy bamboo fly rods) bought a hollow built rod, and to be sure it was hollow built, took x-rays of it,,, and it was indeed hollow built.

Wonders never cease.

<*)))><

thanks art, but tom's right, i wasn't talking about graphite. i think his clarification really helps those very new to this. i AM just glad we were able to throw in some lines showing the differences between the words spine and spline. it drives me crazy to see people use them interchangeably, or say "there's no difference so who cares."

eric
fresno, ca.

Thanks Art and Tom. I know absolutely nothing about the art of building bamboo fly rods. Got to do me some reading up.
Tom, you said "spine is not a physical thing". Could we say it is a characteristic induced by the manufacturing process whether it be fiberglass or bamboo ?