Spines, Splines & Backbones

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What is a spine, spline, backbone, or whatever it is you call it? This is one of the most often asked questions of novice custom rod builders. Of the three terms used above, the most correct one is"spine". "Backbone" may also be used and is not incorrect, but "spline" is not acceptable. Spine, as defined by Webster is "something resembling the spinal column or constituting a central axis or chief support". Backbone as " the foundation or most substantial or sturdiest part of something. Spline is "a key that is fixed to one of two connected mechanical parts and fits into a key way in the other; also a key way for such a key". As defined above you can see that either spine or backbone may be used.

What we are describing in rod building as the spine is that when a blank is bent or placed in an arc as seen when fighting a fish, the rod will bend along a certain axis naturally, at the top of this arc is the spine. All tubular blanks have a spine to some degree. The perfect blank would not have one, but it would have to be manufactured by some other process than is currently being used.In building a quality custom rod, we have to take the spine into consideration. I remember going out on party boats in the Bay Area before the advent of mooching as the primary way of catching salmon. Trolling a 3 pound ball with a sinker release was the preferred method. Looking at many of the rods in the rod holders, I would see the guides and reels on a great many of these rods sitting at all different angles off of the way the rod was actually bending. If these rods had been built properly, the guides would have been sitting on top of the rod, rather than twisted off to the side.There are a couple of different ways of locating the spine on blanks or rods. First wrap a piece of masking tape around the blank about 1/3 to 1/2 the way up from the butt. Hold the blank as close to the tip as possible with the open palm of one hand and have the butt resting on a smooth hard surface. Press down firmly with your free hand in the middle of the blank. You will notice the blank will roll to a fixed position, mark the masking tape in a line on the top of the blank. (See illustration 1). Now continuing to apply pressure, try twisting the blank away from that position and you will see that it wants to return to that marked position. This is the effective spine of the blank. The reason we call this the effective spine is that if you checked small sections of the blank this way you would see that the spine would be at different angles to the mark that you made on the masking tape. You need to check the spine over the longest length possible to get the average or effective spine.

The ideal distance is from the butt to the tip, or as close to the tip as possible. A better way of finding the spine is with a spine finder, which was invented by Ko Watanabe of Fresno back in 1981. This consists of a tube with ball bearings at each end and mounted at an angle. The butt end of the blank is placed through both bearings, pressure is placed on the tip with your hands or with a weight and the rod will into an arc with the spine on top. (See illustration 2). No matter which method you use, if the rod you are building is a conventional or casting rod, the reel seat and guides will be placed on the outside of this natural curve. If you are building a spinning or fly rod, the guides will be placed on the inside of this curve.(See illustration 3).