Tuesday, November 1, 2011

Can you pleasew explain the terms "bend point" or "flex point" in regards to shafts?

Bend Point/Flex Point are terms from the "old days" which we really wish would just die and go away, never to be seen or heard of again. They evolved from a very old mechanical test done on shafts in the 1950s which had absolutely no relevance to how a shaft actually bends during a swing. The old bend point test involved fixturing a shaft so you could apply a pushing force inward from both ends of the shaft. The shaft bowed in response to this and the highest point of deflection was considered the bend point. Problem is that there is never a time during the swing in which a force is transmitted up the shaft form the tip and down the shaft from the butt. So the test and term is not relevant at all and needs to be discarded completely.

Then the industry moved to doing their bend point test by hanging a weight from the tip end (normal deflection test) and noting the point of maximum deviation from a straight line drawn from the tip to the butt. While this form of bending of the shaft was more relevant, the problem here is that if you do this test on every shaft you'll find the difference between the highest and lowest bend point is less than 2inches.

What we have instead are different bend profiles, or rather, differences in the distribution of stiffness over the full length of a shaft. This gives rise to generic terms like "tip stiff", "tip flexible", "butt stiff", "butt flexible" and so on. As generic terms, these too are not worthwhile because they are not specific enough to allow anyone to use them to compare shafts accurately from a fitting standpoint.

Which moves us into the graphs that are the key element for shaft comparison in the Bend Profile software where over 1200 shafts have been tested all along the length of the shaft every 5 inches. Something like this is FAR more relevant for comparing the stiffness design of shafts so as to know more about how the shafts differ in stiffness design, WHERE they differ on the shaft and by HOW MUCH.

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