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Fishing rod spines, splines and guides

December 9, 2010

Rod sections are not always equally stiff in all directions. They sometimes have what is called a ‘spine‘ or ‘spline‘. There is an ongoing debate amongst rodmakers, and some confusion, about where guides should be placed relative to this spine or spline and where in fact the spline or spine is located.

For the most part this is pretty much a debate of little consequence but in certain instances, where a rod has a pronounced spine, getting the guides in the wrong orientation can make the rod twist in your hand when fighting a fish or casting a long line. Clearly it is important therefore to consider where to place the guides in these instances.

I am of the school of thought that the guides should NOT be placed on the spine or at 180 degrees to it but rather at 90 degrees to it. I am often told this is ‘counter intuitive’ but to me it makes sense. This is my reasoning:

If you used an ordinary measuring  ruler as a fishing  rod, on which side of the ruler would you mount the guides – on one of the wide sides or on one of the narrow sides? Answer – surely one  of the wide sides. Why? Because the ruler bends naturally over the wide sides. It would twist in your hand ‘trying’ to bend over a wide side when casting or when fighting a big fish if the guides were mounted on a narrow side. Why does it bend naturally over the wide sides? Because it is has less material to prevent bending and is less stiff in that plane.

So from the ruler example we can derive the principle that, in order to prevent twisting, we should “orientate  the guides in line with the less stiff plane”.

The same principle can be applied to a round section rod with unequal stiffness planes.  Orientate the guides in line with the less stiff plane. Which is the less stiff plane?  One that is perpendicluar to the stiff plane NOT in line with it – think again of the ruler.

Some of the confusion comes, I think, from the use of the term ‘spine’ or ‘spline’ . To me the word ‘spine’ suggests ‘backbone’ and therefore indicates ‘strength’ and ‘stiffness’ . For me, the ‘spine’ is therefore in the stiffer plane (it in fact causes the stiffer plane). A graphite rod has unequal stiffness planes, and a ‘spine’,  because the cloth out of which the rod is made has to overlap itself. The wall thickness is thicker along the overlap and this makes the rod relatively stiffer in that plane. The overlap is the spine. See this illustration

When, as Wayne Cattanach suggests,  one supports a hex bamboo rod section in one hand and rolls the ferruled end on a surface to establish the point at which it ‘kicks’, the kick occurs  as the rod moves off the stiff plane (spine)  onto the next flat which has a less stiff plane. The guides technically should therefore be placed on the flat on which the rod ‘lands’, not the one that it kicked off (the spine). I say ‘technically’ because in reality, with a well made bamboo rod, I don’t believe the spine is pronounced enough to induce twisting, which is after all what we are primarily trying to avoid.

As a further explanation consider these questions:

1)  Do you agree that if you put the guides on the narrow flat of a rectangular rod, the rod will want to twist when you fight a big fish or cast a long line?

2)      In which of the following 2 scenarios would you say the spine/spline is more likely to be directly on top of, or directly underneath, the rod ( i.e. facing the ceiling or facing  the floor) ?

Scenario A – You clamp the grip of a rod blank on a table with the end cantilevering out. You hang a weight on the tip and the rod deflects, say,  1 foot.

Scenario B – You rotate the rod through 90 degrees and re-clamp it to the table with the end cantilevering out the same amount. You hang the same weight on the tip and the rod now deflects, say, 2 feet.

3) In which of the scenarios in question 2 would you recommend placing the guides facing the ceiling or floor?


1) I think you have to agree. If you don’t, try this experiment.  Place a cuphook in the narrow side of a long thin rectangular section of timber at one end. Clamp the other end of the timber to a table with the cup hook end cantilevering well off the table. Hang a heavy weight from the cuphook and see what happens. Roll the section through 90 degrees, reclamp, re hang the weight and see what happens. I guarantee the timber will try to bend over the wider flat in both instances and will twist to do so if necesary.

2) If you answer ‘A” then we are in agreement about what the term ‘spine’ or ‘spline’ refers to and which plane it located in the stiff plane. if you answer ‘B’ we have different meanings for the word ‘spine’ and we may well still agree on where the guides should be placed in principle

3) If you agree with question 1 and answered ‘A’ to question 2 then you have to answer ‘B’ to question 3 – because the rod in the scenario could be a rectangular one – and we are then in agreement that the guides should NOT be orientated in line with the ‘spine’ or ‘spline’

That’s the way I see it. I may very well be wrong. After all , the rods I build tend to have negligible spines, if any, and that may be why I have not had an issue with twisting. Whilst I believe my reasoning is sound I would welcome a convincing argument or explanation to the contrary.

3 Comments leave one →
  1. Ron Hossack permalink
    December 10, 2010 9:53 pm

    Well this is nice thought about how and where to apply the guides.

    My method is different (probably wrong too) but I use a table and place the tip under the table edge and rotate until it jumps and I mark that spot.

    Now if I place the guides on the mark I can cast farther and if on the opposite side I can pick up the fly off the water easier …

  2. September 20, 2011 3:37 pm

    Makes sense Steve …


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