I'm turning my old beach rod into a two-piece.
When I cut it in half the spine on the butt end remained where it was however the spine on the top half shifted almost a quarter turn.
Is this common?
Does it just mean that before there was tension in the blank?
Is this just a characteristic of the construction - the tip end glass wraps were not lined up with the butt end glass wraps? Perhaps poor construction?

I never experienced the rod "wanting" to twist - it behaved fine.

Thank you
Robert

The spine is not a thing - it is an effect. Therefore, you get the effect over the length of the blank you're flexing. Now that you're only flexing the tip by itself, you're seeing the effect as it occurs on that particular length of the blank. It hasn't shifted - you were just getting the effect over the entire length previously.

Fish don't jump out of the water and grab our rods with a fin and start flexing the blank. They can only load our blanks via the line running through guides attached to the blank. For that reason, spine has little to no effect on rod twist. All rods with the guides on top will be inherently unstable and will attempt to twist under load. Rods with the guides along the bottom of the blank will be inherently stable and won't twist under load. The load will always tend to pull the guides under the rod (or in the direction the load is coming from, which in the case of a fish is generally from below).

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

Robert, I believe this to be normal. The spine is an average of the of all the different tensions that result from the manufacturing process (someone else will be able to word that better than me). Therefore the average will be different in different parts of the rod compared to the rod as a whole. For example I make multi piece fly rods. The individual pieces spine differently to when they are joined and spined as a complete rod/blank. Hope this helps John

Robert,
There are half a dozen different things that contribute to the effect we call spine. One of the things that contributes is the alignment of the graphite fibers themselves. When a blank is constructed the edge of the material, called prepreg, is tacked to a mandrel but because the mandrel is tapered as each additional layer is wrapped on the mandrel the fibers become increasingly misaligned. The outer most layers, the ones that contribute most to the blanks stiffness, will tend to spiral up the blank. This results in the spine on many blanks also tending to spiral up the blank. What you have seen is normal for many blanks.
This also causes the spine to tend to move based upon how much the blank is deflected. Often the amount that the spine moves with additional deflection is not much and hardly noticeable but on some blanks it is very noticeable.
My suggestion would be to ignore it and don't worry about it. It isn't going to hurt anything.

I thought I was the first poster, if I had seen Toms post first I would not have posted...explains it way better that I could/did. John