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Spline Alignment: Does it matter?

Discussion on tenkara rods

Re: Spline Alignment: Does it matter?

Postby jd_smith » Mon May 06, 2013 9:16 am

rmcworthing wrote:Hmm. That's interesting.

I'm not a rod builder, but this is different than the explanation of tenkara rod construction I received from two major Japanese manufacturers. They explained that there is no true spine in a tenkara rod. There is, I was told, a false spine created by the carbon fiber layering process, which the manufacturers seek to eliminate. However, I was told there is no structural spine, as would be found in a Western fly fishing rod, spincasting rod, baitcasting rod, etc.

One manufacturer told me that some tenkara rods were made with a sinusoidal or spiral structural spine variation, but this was not the rule.

Daniel, could you clarify? Would you classify the spine you describe on Tenkara USA rods as a false spine or structural spine? Or am I just way off on my understanding?


Hey Rob,

I'm not always the best at describing things but let me take a stab at "what is the spine and what is the false spine".

When checking for the spine of a rod blank, there is a point when the blank is being rotated under stress that you will feel the blank sort of hop upward and then quickly rotate to a relaxed position. This relaxed position is commonly known as the relaxed curve. The exact opposite of the relaxed curve is known as the spine, and is more rigid and resistant to stress.

The description Daniel gave of overlapping cloth leaving a thicker wall or a thinner wall depending on what side you're looking at is correct and is in direct correlation to the spine effect. More material in one location creates more resistance to stress.

What happens sometimes but not every time with a rod blank is when you do the same stress test to determine the spine, the rod blank will hop or exhibit resistance to stress in two different locations. One of the locations will not be in the exact opposite position of the relaxed curve. This second location that exhibits a stiff spine or resistance to stress is known as a false spine because it is not located in the direct opposite position of the relaxed curve.

So to be clear, every rod blank has a spine and some also have a false spine as well. It is my experience that rods built on these blanks are harder to build and are of a lesser quality because the manufacturer paid less attention to how the cloth was cut and laid on the mandrel creating two noticeable thick spots (spine and false spine).

I don't think that any rod manufacturer (fly, spin, casting, boat or any other) actually adds a structural spine into the blank, or actually tries to create a thicker side of the wall thickness by overlapping more material on one side than the other. I think the overall goal is to minimize this effect as much as possible. I may be wrong about this "structural spine", I don't think I am, but I have never heard of it.

I think that what was described to you by the Tenkara rod manufactures is correct but possibly slightly misinterpreted. This is my interpretation. A tenkara rod is assembled in a randomized extension of its pieces with no thought given to the structure or "alignment" of the individual spine of each segment. Thus it has no "structure" of the spine in the overall length of the rod. When adding guides to a fly, spin, casting, or boat rod blank, there is often an effort to "structure" the rod to have the guides in line with the spine, whether they are placed on the spine e.g. casting or boat rods, or on the relaxed curve e.g. fly or spin rods. Thus having a structured or aligned spine throughout the overall length of the rod..


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