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Rod Design & Construction - an overview

Our May 2001 contribution from Terry Lawton

A fly rod propels the fly, the business end of the tackle, to the trout. Without a rod that will cast a good line, it is impossible to fly fish for trout or salmon. Fishing rod design and manufacture has progressed a fantastic amount over the last 50 years and the modern fly rod is a very advanced and highly technical piece of sporting equipment. Terry Lawton looks at the design and manufacture of fly rods in this article which is an introduction to a forth-coming series on home rod building.

"The rod makes the 'angle' and, without it, a fisherman is not an angler."

It is the rod that propels the fly, the business end of the tackle, to the trout. Without a rod that will cast a good line, it is imposible to fly fish for trout or salmon. Fishing rod design and manufacture has progressed a fantastic amount over the last 50 years and the modern fly rod is a very advanced and highly technical piece of sporting equipment.

BLANKS

Carbon fibre or graphite rods have revolutionised fishing. The introduction of this material was accompanied by a new term: modulus of elasticity. Modulus is simply the measure of stiffness per weight of material: its resistance to bending. Carbon fibres are simply much stiffer and lighter than either fibreglass or bamboo. Hence carbon rods are lighter for a given line size and length than any other rod. Manufacturing rods from carbon fibre gives them a consistency of action and performance.

Carbon fibre is available in different grades and rods are being made from ever higher modulus carbon fibres. A typical modulus of elasticity for a mid-performance rod is about 35,000 psi while a high modulus fibre would be 45,000 psi, or even more. A high modulus material has a higher resistance to breaking as well as its increased resistance to bending. High modulus graphite rods can be lighter, with a faster recovery and smaller in diameter.

Graphite is normally made in long rolls with all the fibres running the length of the roll. It is coated with a bonding resin. The fibres have to be reinforced and there are two ways of doing this. A small amount of fibreglass can be added to give hoop strength and the second is to wrap additional graphite fibres spirally around the blank. The latter method is the most versatile and produces a blank of 94 to 96 per cent graphite, a higher figure than can be achieved by adding fibreglass. The balance of material is the bonding resin.

Rod blanks are made on tapered steel mandrels. It is the design of the taper/mandrel, whether a straight taper or a complex one, that determines the performance of a rod. The choice of material is secondary: good materials will not make a badly-designed rod cast better. Mandrels are made to a precise design of taper as it is this that produces the correct action and size of rod blank. The rod designer's skill lies in designing a taper that will produce the desired result in terms of action and casting performance, by balancing the diameter of the rod shaft and its wall thickness to produce the desired result. Although it is possible to make a rod blank on a long mandrel and then cut it into the correct lengths, this is not the way that a quality rod is made. Each section of such a rod is made on a mandrel specific to that section.

The carbon cloth is what is known as a pre-preg: it is impregnated with a resin that is cured by baking in an oven at a set temperature. A precise pattern is cut from the sheet and rolled round the mandrel. This can be done under pressure or a shrink tape is wrapped round the outside of the carbon cloth on the mandrel. The mandrel is now baked in an oven at a precise temperature and for a precise length of time to cure the resin. The cured blank is removed from the oven and the mandrel is withdrawn.

The ribbed effect left by the tape is removed by grinding the blank. The better the quality of the blank the smoother the finish. Matt-finish blanks are left unvarnished, or varnished with a matt or satin varnish. Carbon fibre is usually dark grey: the colour that we associate with carbon rods. Rods, or blanks, which are a different colour have been painted. This is done by passing the blank through a reservoir of paint in one continuous movement to ensure a smoth and complete coat of paint.

It is the final alignment of the edges of the carbon cloth and minute variations in the pressure applied by the shrink tape that result in rod sections having a more or less distinct spine ie they are stiffer or more resistant to bending in one plane than another. The relationship of this spine to the rings plays a major role in the casting performance, and thus enjoyment, of a rod. As the design and manufacture of rod blanks advances, the influence of the spine is being reduced and some manufacturers claim to be producing rods with no discernable spine.

FERRULES

A ferrule is more than simply a means of joining two or more sections of a rod together. Ferrules have an important effect on the overall action of a fly rod. They must be as light as possible for efficient transfer of energy through the rod when casting yet strong enough to withstand maximum rod loading when playing a fish. The best design of ferrule will have the least affect on the action of a rod.

The early multi-piece travel rods were unsuccessful because they had too many metal ferrules: they spoilt a rod's action and added too much weight, particularly near the tip. Improvements started to be made when the first all-fibreglass ferrule come about. This eliminated the weight of metal ferrules and the hinging effect. These early ferrules were the tip-over-butt style which is still used today.

All ferrules create some change in a rod's diameter and a badly designed one can break a rod tube from the leverage applied to the inside of the tube. This can happen just as easily with a two piece rod as a multi-piece one.

Internal or spigot ferrule

Many of the leading rod makers use the internal or spigot ferrule. A spigot is glued inside the butt section; the spigot is a perfect fit inside the top section. To prevent the walls of the top section from splitting, the tube is reinforced with layers of graphite fibres which run perpendicular to those in the blank.

Proponents of this type of ferrule maintain that it provides the most efficient transfer of energy, have a consistent taper through the ferrule and add very little weight. When assembled there is a slight gap between the sections, to allow for wear, and some rod designers do not like this discontinuity of action across the change in diameter.

Sleeve ferrule

The sleeve ferrule has a short graphite or carbon sleeve glued over the bottom end of the top section. The butt section fits into the sleeve. The ferrule is the opposite of the internal or spigot.

There is a continuous taper inside the ferrule which is arguably the strongest type. Critics feel that the sleeve adds too much mass and stiffness, particularly in smaller rod sections, which can interrupt the transfer of energy, and that too much reliance is placed on the glue line.

Tip-over-butt ferrule

This is another popular ferrule but each section of a rod must be made on a separate mandrel. Each section tapers to a diameter large enough to accept the male ferrule of the adjoining section. The female ferrule is reinforced by a layer of carbon wrapped crosswise. Rod action at the design stage has to take into account any stiffening effect caused by the thicker section of the rod shaft at the ferrule.

Flared ferrule

American rod maker Gary Loomis designed and patented this ferrule which is based on the tip-over-butt style. Instead of having a gradually-increasing taper, the rod shaft has a flare at the ferrule, into which the butt section is inserted. The result is a minimum length ferrule.

It is probably the best tip-over-butt style of ferrule and Loomis maintains that rod taper and energy transfer are optimised by the short length of the ferrule. Smoothness of rod action through the ferrule and strength are said to be very good.

Terry Lawton is a passionate nymph fisherman who caught his biggest wild brown trout (in the UK) - 4lb 2oz - on a home-tied variant of a goldhead, Sawyer-style pheasant tail nymph.