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The Best Way to Make Graphite Shafts

With the advancement of composite technology and the recent defense industry build down, we find more shaft makers applying new methods to make graphite shafts.

There are three commonly used methods to produce graphite shafts: the tested and proven sheet lamination process, the seamless filament winding process, and the resin transfer moulding process, that is frequently used to mould irregular-shaped parts.

The question that faces clubmakers is which one makes the best performing graphite shafts. Before an answer can be found, we need to examine in detail the design and production process behind each one of these approaches to shaft making.

In the sheet lamination process, unidirectional ply and angular ply of graphite prepreg (i.e. a thin and flat sheet of graphite fiber bonded together with epoxy resin) are laminated over a steel mandrel to achieve the desired level of strength, stiffness, torque, weight, and kick point.

In the filament winding process, the steel mandrel is held on both ends in the winding machine. The mandrel is then spun at a rate controlled by the machine. Simultaneously, a graphite tow is wound over the mandrel at the angle and density controlled by the designer. In the resin transfer moulding (RTM) process, the shaft maker first needs to design a graphite sleeve braided with a multi-axial braiding machine. The mandrel is then inserted inside the sleeve, and placed inside a two part mould, and when clamped together creates a female cavity of a shaft. Finally, epoxy resin is injected inside the mould with 135 psi pressure, and the shaft is heated to cure.

All three of the processes have their respective strengths and weaknesses. The challenge for any shaft maker will be to determine what kind of material to use, how the material should be used, how to design the tooling, and finally how to control the production process as to produce the optimal shaft at the lowest cost.

Sheet Lamination

Some suggest that sheet laminated shafts are not seamless, and hence, not as good. Designers at Harrison beg to differ. A good shaft designer knows how to design a sheet laminated shaft that demonstrates the same frequency uniformity as a filament wound or a RTM shaft. Even in Dynacraft's "The Modern Guide to Shaft Fitting", several laminated shafts have been tested as having frequency variance of less 3 cpm vs, 2 cpm for the top of the line filament wound shafts. Why should anyone pay more money for a tiny 1 cpm difference?

Filament Winding
Filament winding process also has its own weakness. The most significant one is the lack of control over proper resin content that is inherent in the machine. Therefore, filament wound shafts are commonly made 10% oversize so that the excess graphite can be ground off to produce a shaft with proper outside diameter. This grinding process does not change the fact that the resin content is too high. The shaft is not as strong as laminated shafts, which have a much higher graphite to resin ratio.

The torque rating tested under 1 foot pound static environment may come out the same between a laminated shaft and a filament wound shaft. A shaft with a much lower fiber content definitely will not demonstrate the same torsional stiffness in a 80-90 mph dynamic environment. Naturally, the shaft recovery rate can not be expected to be as fast as a laminated shaft.

Resin Transfer Moulding
The RTM process using braided sleeves is a process that is ideal for making irregular-shaped product. When it comes to designing tubular product, the RTM process is not as versatile as the lamination process. The resin distribution is also not as even as the lamination process. The bottom line is when you can use lamination or filament winding process to make a cheaper and better shaft, why would you use RTM?

Harrison is aggressively seeking new and better ways to design and produce graphite shafts. At the present state of technology, the sheet lamination process is still the most versatile and consistent way to make a golf shaft. We will keep you posted on any new break through in the shaft making process.