A Few Words on 4/5/6 Strip Rods
from The Practical Fly Fisherman
By A.J. McClane, pub. by Prentis-Hall
A fly rod has to bend and work equally well in any direction -up, down, sideways, across the flats or across the corners. You may think that only a round rod will bend in this way; so did the early rodmakers-they rounded off the corners of their rods, but this cut away the most valuable part of the bamboo. The idea of building rods of several strips of bamboo is quite old. They have been built from two to as many as twelve strips. For one reason or other, most of these rods had an even number of sides-four, six, eight, and so on. But the odd angles didn’t get much attention until Robert W. Crompton of St. Paul, Minnesota, analyzed the situation and concluded that the five-strip construction was superior in nearly every respect. Crompton laboriously planed a set of sticks by hand, following the taper of his favorite six-strip rod. Finally it was finished. Trial proved the new five-strip rod much too stiff. Both rods had the same amount of wood, the very same taper, but the pentagonal type felt, as he expected, much stiffer. A great deal of interest was aroused when this fact was brought to the attention of his rodbuilding friends, Dr. George Parker Holden and Perry Frazier, but finding the right tapers for this construction was to evolve over a period of fifty years. He pointed out the five-strip’s merits; no continuous glue line through the center as in evensided rods. The shearing stress or working strains were borne by the bamboo fiber. Then there was about 15 per cent less glue. He pointed out that if a rod were made of a great number of strips, it would consist principally of glue, and glue is no substitute for bamboo. He explained the unusual stiffness by sketching a pentagon-the cross section of a five-strip rod-pointing out the fact that the five corners were opposed by flat sides. These corners were in effect, little backbones that ran the entire length of the rod.
It’s this “backbone” theory that caused conventional rod makers to pop their buttons, and at the same time brought five-strip adherents into a common bond of understanding. But before the argument against, let’s examine the case for the five-strip idea more closely. The leading modern exponent of pentagonal construction is Nat Uslan of Spring Valley, New York. Nat is an old friend of the late Robert Crompton, a master rod builder, and by far one of the keenest artisans in his trade. In the Uslan school of design, the argument against evensided construction is that corners are opposite corners and flats are opposite flats. The corners, in the five-strip rod, act as backbones extending the length of the rod, but in four- and six-strip rods they are in the same plane-that is, directly opposite each other. Since there are three pairs of flats, it follows that the action, or bending, will occur in one or more of these three planes. In theory, if the fisherman forces a corner to take some of the load, it simply “shrugs” the load over to one of the adjacent flat sides, with the result that the cast doesn’t go exactly where he directs it. This is an inherent characteristic of all rods having an even number of sides according to the pentagonal theorists.
A five-strip rod doesn’t respond in such a manner. In this case each “weak” flat has a reinforcing backbone on the opposite side. Naturally, the strengthening is greatest right at the five corners. At points slightly to one side or the other of these corners the effect diminishes slightly only to increase again to full value as the center of the bordering flat side (remember that there is a corner opposite this flat) is reached. A four-sided rod prefers to bend up and down and sideways. To use shooters’ parlance, it wants to swing directly from twelve to six o’clock or from three to nine, but it resists bending slightly more in any other combination. By the same reasoning a rod of six-strip construc-tion will flex easily from twelve to six, from two to eight, and from four to ten. It, too, is reluctant to bend in any other direction. The five-strip rod is no exception to this tendency to follow paths of least resistance. But where are these paths and how many of them are there? According to Nat Uslan they’re not at corners because these regions are strongest; nor are they at the flats because, as pointed out before, there is always a corner opposite a flat. Then these “flexing planes” must necessarily lie somewhere between a corner and the next flat. Since there are ten such combinations of corners and flats, we can assume that the five-strip rod doesn’t care which way you shoot your cast. This is the essence of pentagonal design, and right or wrong, there’s no question but that Nat Uslan makes a fine fly rod.
The six-strip or hexagonal fly rod is the traditional construction among rod builders the world over. Ever since a gunsmith by the name of Samuel Phillippe, of Easton, Pennsylvania, began playing with bamboo strips back in 1845, speculative rod makers have championed every possibility, from two strips to twelve. But Mr. Phillippe’s six-strip rod caught on, and it remains today as the crème de la crème of even-sided building. Now the proponents of Phillippe’s school have some sound arguments against five-strip theory, and the two things they talk about in comparing the five and the six are weight and stiffness. The weight depends on the area of the cross-section, so when you compare cross-sections of these two rods you are really comparing the weights of the five and the six. So if the two cross-sections are of the same area, this indicates the same weight. The other factor, stiffness, is measured by what an engineer calls the “moment of inertia” of a cross-section. (The moment of inertia of a circular cross-section varies as D4, or the diameter to the fourth power. Thus a circle one inch in diameter is IxIx1x1=1. A circle 1.1 inch in diameter is 1.1x1.1x1.1x1.1=1.45 or almost 50 per cent stiffer.)
This is the point on which rod builders of the two schools really disagree. The fact is that if the cross-section is made up of any number of equal triangles with their inner points on a common center, their outer points on one circle and their outer flats on another circle-the rod will be equally stiff in every direction. And that holds true whether the cross-section is a triangle, a square, a pentagon, a hexagon, a septagon, an octagon, or in fact a figure with an infinite number of sides-a circle.
All fishing rods which have guides and reel attached tend to cast in a preferred plane, because the center of gravity of the whole outfit is offset from the center axis. If you bend a piece of hexagonal split cane in your hands, it will feel stiffer bent across corners, because the pressure applied to your hands, in pounds per square inch, by a corner is greater than that applied by a flat. You get exactly the same false impression by bending five-strip “flat-up” and “flat-down”; the latter feels softer.
Any construction consisting of a regular polygonal crosssection having four or more sides will have the same deflection for a given load irrespective of the plane in which it is bent, whether across corners or across flats. Richard Walker, well known British angling writer, even took this problem to Cambridge University to get a precise, mathematical explanation, and this is what he concluded in a recent letter to me:
The rigidity of a rod depends on the moment of inertia of its crosssection, and the values for various constructions are as follows:
Having come thus far in this mathematical orgy, you may be disturbed by my clinical treatment of this precious thing called a fly rod. No doubt you care not a fig for analysis, so long as the rod gives you pleasure. But before we can set forth in straight-forward speculation about fishes and their ways, we must first see to our tools in order that we are not left in the frivolous ranks of gullible anglers. Our rod engineers are arguing, and now, to some extent we know what they are arguing about. At this point I would like to offer my own opinion and say that I own four-strip, five-, six-, and seven-strip rods, and all but the seven-strip construction is good. I think all these didactic discussions have no future because the most important ingredient of a rod, and one which is never discussed, is its taper. In finding the perfect rod with any kind of cross-section one must find the perfect rod for that length. This is purely a rod builder’s problem, and one in which we won’t get lost. Let’s offer this thesis to posterity so
that when historians dig among our ruins a hundred years hence they will find some kernel of controversy which they cannot disprove. So now we’ll look at other forms of construction, ignoring the strips and considering the material.
© 1975 Prentis-Hall