from The Wise Fisherman's Encyclopedia
Selection. There is no known method of infallibly appraising bamboo without using
elaborate testing equipment. Two factors, however, are readily apparent:
(1) weight, and (2) appearance of the end grain. A culm of bamboo 8 feet long and
13/4 inches average outside diameter should weigh approximately 4 pounds. This
figure represents the upper limit for stock that was cut low, near the ground (the
butt portion), and seasoned for perhaps from six months to a year in a dry location
(the attic in the case of amateurs).
In viewing the end grain, notice in particular the character of grain and fiber structure at the outside edge, just -under the enamel or cuticle. In most cases this is an exceptionally dense, close-grained substance. Taking note that the cut end does not occur in the immediate vicinity of a node, this dark amber-colored layer should extend, with very slight diminution in density, inwardly at least 1/8", preferably more, say 3/16". Now examine the other end. Here again the compact fiber layer should represent possibly one-third or more of the total wall thickness. Since but two areas can be examined, one must hope that the material between is not of greatly differing character.
If it is at all possible, examine a number of culms in order to gain a good degree of perspective. It is far simpler to isolate a single excellent specimen from a number of fair ones, than to appraise a single culm without reference to others. Straightness, although desirable, can be sacrificed to a degree in favor of weight and fiber disposition. This not mean that crookedness is to tolerated, for if the culm is to be split the strips will then be quite crook difficult to work, and will require considerable straightening during gluing.
If the culm is to be sawed into strips the path of cut is a straight line, crossing the grain throughout the bent area. It is the writer's opinion that if the angle so produced does not exceed a ratio of one to twenty, i.e., a divergence of the grain lines from the sawn edge in the amount of 1/4" in a running length of 5", no noticeable ill effect will manifest in the finished product either from the standpoint of strength or action.
A final consideration is the appearance of the outside surface. Freedom from stains, watermarks, etc., appeals only to the aesthetic sense and has no functional value at all. However, a close examination must be made to determine the extent of surface damage such as pin holes, locally crushed spots, diseased or decomposed areas, knife slashes, etc.
PLASTIC IMPREGNATED BAMBOO
The initial pioneer work in the plas impregnation treatment was done A. J. Stamm and R. M. Seborg of U. Forest Products Laboratory at Madison, Wisconsin. The "IMPREG" process, it is named, was originally developed to prevent excessive swelling and shrinking of wood due to variations moisture content. The wood is impregnated with resins which serve as block, preventing the entrance of moisture into the cell structure of the wood.
Methods. Two methods of treatment are in current use. The first is a simple
immersion in the plastic solution, liquid diffusing through the fibre structure. The
second method involves a closed tank. Wood immersed in a trough inside is
subjected to an a pressure of 20 to 75 pounds per sq inch, forcing the liquid into the
fibre structure. This procedure is usually employed only when relatively thick
pieces are to be treated.
The plastic ordinarily consists of phenolformaldehyde mixed with water such proportions as to add 80 or 40 per cent of resin, by weight, to the measured dry weight of the wood. After soaking, the impregnated pieces are placed in a kiln and heated at approximately l50 F for several hours to drive off the excessive moisture. The temperature is then raised to 200 F, or more, to set (polymerize) the resin.
Purpose. The primary function of the process is to deposit a waterproof solid throughout the fiber structure, as well s along the wall surfaces of the wood or bamboo cells. It is not intended that the coarse open grain be impregnated completely, as this would merely add weight without rendering additional benefits from the waterproofing standpoint. All that is apparently necessary is a complete covering of the inner fibers and cells; and in bamboo, at least, weight deposit (measured after drying and curing) of 20 per cent is considered adequate. Although figures are not available regarding changes in the strength of bamboo as a result of plastic impregnation, some information is given on the effect in other woods. Maple, for example, when impregnated with 20% phenolformaldehyde is increased in compressive strength by 18%. Tensile (tension) strength is increased by about 8%, and resistance to crushing is increased tremendously to nearly 70%. The author believes that it can be safely assumed that bamboo will respond in like fashion. Bamboo strips can be processed prior to gluing into sections, or the glued up section may be treated. Aside from imparting water and weather-proof characteristics to the cane, undoubtedly the most outstanding feature of impregnation lies in the appearance of the finished product. Ordinary finishing operations impart a surface of extraordinary beauty -satin-smooth and dark mahogany in color-and any further treatment would simply "gild the lily," from both the functional and the aesthetic viewpoints. Disadvantages. Minor drawbacks do exist with this process, however. First, is the increase in weight. Some rod makers prefer to use cane of a more dense fiber concentration, that is, bamboo possessing a naturally heavier growth. Secondly, the "Impreg" process cannot make good bamboo from poor stock. Superior cane must therefore be selected if a superior product is desired, and the extra impregnating and curing operations obviously increase the cost of production. Finally, the relatively long time and high temperatures required to harden the resin is, in the opinion of some rod manufacturers, damaging to the bamboo fibers. There are, however, two schools of thought on the subject and any opinion expressed here would be challenged.
STRUCTURE OF BAMBOO
Wood. The principal points of differentiation between bamboo and ordinary wood are in the basic structure of the materials. Wood, in the usual sense, is a relatively homogeneous structure composed of hollow irregularly shaped cells. These occur in a quasi-regular vertical and horizontal disposition. Characteristic cells are composed of cellulose and generally are considerably greater in length than in breadth. The average size of any individual group of cells depends somewhat upon its position in the log. Between annular or growth rings, the structure is quite open, the cells being relatively large. In the region of the annular ring itself, the density is considerably greater. A sample taken near the center of the timber is normally more open-grained than one taken near the surface slightly below the cambium, the sap layer just under the outer bark.
Bamboo. The growth structure of bamboo is entirely different than that presented by wood. The coarse, open cell structure so characteristic of the various woods is totally absent. In its place are found bundles of microscopic fibers laid parallel to each other, much like the strands within the sheath of a bridge cable. The spaces between adjacent bundles or cords of the bamboo are filled with a thermoplastic resin. Toward the outer surface of the hollow shell the number of these fibrous strands increases rapidly. Just below the outer protective enamel, bamboo is composed almost entirely of these cellulose fibers. Thus, considered from the innermost surface outwardly, the fiber structure, density, and strength of bamboo vary enormously. From the standpoint of use as a rod-building material, this inherent characteristic is most desirable.
Advantage of Bamboo. When cut into strips, mitered, and glued to form a rod
section, this varying density, in effect, locates the strongest portions of the bamboo
along the outside of the rod, and those not so strong about the centerline. The rod
can then be visualized as a many-sided shell under which exists a continuous
bulkhead which serves to prevent collapse or bulging walls.
Under normal conditions the strongest possible beam-and a rod is one form of a beam-is one built in the form of a thin hollow tube. In actual practice, however, when such a beam is bent sufficiently it will fail at a load less than that which it could theoretically support. The failure is caused by collapse of the wall. Anyone who has ever bent a tube or pipe is quite familiar with this effect. In order to render the thin cylinder less liable to this type of breakdown, a brace or bulkhead must be installed inside. A single such brace would serve only locally and create a critical condition elsewhere in the tube. Therefore, a number of bulkheads must be incorporated to maintain the wall in its proper circular state. Obviously, to realize the ultimate in beam strength, a great many of these closely spaced partitions are needed inside the tube.
In the manufacture of tubular rods, a compromise is drawn by decreasing the outside shaft diameter and increasing wall thickness. This effectively lowers the liability of failure due to collapse of the shell. Bamboo, by its very nature, disposes its structure efficiently, which is most fortunate for those who use this material in the construction of their rods. Although inferior to most metals and glass in absolute tensile strength, the bamboo compares very favorably in actual use due primarily to its relatively low specific weight. An approximate strength-weight comparison is made in the following table:
Bamboo vs. Glass. Indications, then, from the figures given before are that, for a given weight, a glass fiber rod of tubular construction will be two and two-thirds times as strong as a comparable weight of six-strip split bamboo The truth of the figures cited is contingent on several variable factors as follows:
It follows, therefore, that to realize the advantages of high strength materials, a high degree of precision and quality control must be rigorously pursued throughout the entire manufacturing process.
In an endeavor to circumvent the vagaries inherent to the physical properties of natural rod-making materials, engineers have long sought to manufacture a substitute. Strength characteristics of all structural materials have been of common knowledge for many years. The ultimate goal represents, therefore, material with the highest strength to weight ratio possible. Glass is one of these substances. It possesses fantastically high tensile and compressive strength, is extremely elastic, and has an almost infinite fatigue life-all most valuable assets insofar as fishing-rod material is concerned.
Because of its brittleness, it is impossible to make a usable rod out of a simple stick of glass. Therefore, it not until a process of drawing glass filaments to microscopic diameters evolved that the use of this material fell into the realm of possibility. By virtue of the extremely small size of these slender fibers, brittleness was eliminated.
Once this process was developed, a long series of experiments was conducted to unearth a satisfactory means of bonding the necessary multitude of tiny fibers into a strong and compact rod. Phenolic impregnated paper and cloth products had enjoyed considerable success in bus commercial fields, including the anufacture of aircraft propellers. The reinforcing fabrics were, however, easily wet or "soaked" with the impregnating fluid, resulting in an extremely homogenous end product. Therefore the search was for a thermosetting plastic material that would wet the smooth surface of each fiber and maintain intimate contact throughout the curing cycle.
The first successful rod of the plastic bonded fiber glass combination was announced shortly after World War II. This example, currently sold under the name of Wonderod, is built by laminating glass fiber about the outside of a wood filler. In this way the basic structure of bamboo is more or less duplicated - a continuous, low weight bulkhead extending through a circular outer layer of working fiber.
Other rods soon followed, the first types being of hollow tubular construction, and eventually a bait casting version of solid plastic-glass fiber was fashioned. This differs in that a glass fiber fabric is employed rather than the floss characteristic to the others. Several turns of the fabric are taken about a very precisely tapered mandrel, and the plasticizing agent is caused to completely fill the spaces between the individual threads of the fabric. The application of heat hardens or sets the plastic matrix, bonding the whole into an exceedingly durable mass. Sections of this sort are being marketed for those who wish to assemble their own rods.
Disadvantages. If, then, the physical properties of fiber glass rods are so
outstanding. what are its drawbacks? In the first place, the high strength, elastic,
tireless character of the glass fiber base is not a trait of the plastic bonding agent.
Fatigue life of the filler material is a point of cardinal importance. If the glass is to be
expected to flex ten million times without failure, then the matrix must be able to
cope with an equal number of flexings without breaking down. Most plastic
materials when subjected to stress reversal gradually show evidence of
microscopic cracking, which appears under a microscope somewhat maze-like or
mosaic in pattern. This cracking continues with use until the entire plastic
structure has broken down and is held in place only by the fibers extending through
the individual particles. Archers will recognize this as a symptom of old and
useless bows. Urea plastic bonding agents are apparently susceptible to such
breakdown, as early experiments with urea bonded glass fiber met with failure.
A second important phase of glass-plastic rods regards the dimensional accuracy
attending the fabricating processes. By the very nature of its high strength, great
pains must be exercised in the symmetrical distribution of the glass fiber material.
An assymetrical disposition results in a definite stiffness in one plane, or knock as
it is termed among professional rod makers. This is one of the most troublesome
problems of this form of rod construction, especially through the small tip sections.
Excellent examples of both cored and hollow types have come to hand, proving that
it can be done. Until such time as the knock can be consistently held to
insignificant proportions, the makers of bamboo rods need feel no qualms about
their future, at least not from this quarter.
Thirdly, at this writing there appears to be some difficulty in mounting ferrules permanently to the glass-plastic rod sections. It is suspected that the nature of the plastic itself is the offending factor. When installed, properly fitted ferrules are pressed onto the rod end with, perhaps, a .002-inch tight fit between the metal sleeve and the plastic-glass shaft. This places a relatively high compressive stress upon the plastic. This stress causes the plastic to yield (cold flow) enough to relieve the stress. A zero clearance condition-neither tight nor loose - then exists, with only the adhesive properties of the ferrule cement holding the pieces together. Resin base ferrule cements, while extremely tacky when warm, are quite frangible when cold, and protracted use of the rod under such circumstances will reduce the cement to powder. Several elastic adhesives have been developed that apparently will tolerate indefinitely this semi-loose condition. These substances do not harden, but when properly cured take on a ligament-like toughness with an ability to yield slightly under stress, and to recover fully the moment the stress is removed. At least one fiber glass rod manufacturer