November 2008 Golfsmith Clubmaker Back to Main
shaft talk
GD Flex and MSI
by: Dana Albert
Brand Specialist, Graphite Design

Editor’s note: For almost 20 years, Graphite Design International has been manufacturing top-quality golf club shafts and driving technological innovation in the field. Clubmaker recently asked Graphite Design to share some of their production techniques with our readers.

What is GD Flex?

When we design a new shaft for our OEM or aftermarket partners, there are multiple target specifications for each bend profile. Different tip and butt diameters and taper rates are chosen for different trajectory goals. There are thousands of different designs with thousands of different bend profiles and balance points.

Once the initial parameters are identified, a mandrel is chosen to provide the core of the material rolling. Mandrels are solid steel staffs, typically about 63" long for wood shafts. Iron shaft mandrels vary, and for constant weight profiles, there are individual mandrels for each length and weight.

The pre-preg composite materials are hand rolled onto the mandrel, the resin content acts like glue, and once heated, the material becomes malleable. The pre-preg is cut into flags that are typically triangular in shape. Different flag sizes predict where the shaft will bend or not bend. The bending is created from the taper rate. Most tubes bend very little if they are perfectly parallel.

The stiffness of the material and target weight of the shaft will predict different types of feel through impact. The feel through impact is the “unloading” of the shaft. The amount of load or bending is first targeted as a “GD” flex. The GD Flex measures the bending stiffness of the entire shaft, which includes the tip and butt stiffness.

Frequency measures stiffness in the first 20"-25" of the butt section of the shaft. Take, for example, two shafts that have identical frequencies but have a wide variation in tip stiffness. These shafts may appear to be the same in an assembled golf club, but the difference in tip stiffness will have a huge impact on the trajectory of the golf ball. Typically, a weak-tip shaft will produce a higher trajectory than a stiff-tip shaft in the same loft clubhead. With today’s larger heads, tip stiffness translates into increased stability on off center hits. When we design the tip structure of the shaft specifically for a particular shaft type, the golfer receives the maximum accuracy and distance benefit.

What is MSI?

Material Stiffness Integration, or MSI, is the design concept by which Graphite Design develops shafts. We believe that by combining materials of different stiffness and fiber volumes, we are able to reduce unwanted vibrations while promoting enhanced feel.

Composite materials consist of two components: fiber and resin. The stiffness of each fiber type has an impact on how much vibration, or feel, is transmitted up the shaft. The resin acts more like a sponge, absorbing vibrations. By integrating materials of different stiffness and fiber/resin percentages, we can promote better feel. Using low-resin-content materials equates to more fiber, which means higher-strength shafts with better feel and distance. Graphite Design is one of the largest consumers of low-resin-content composite materials.

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