RE: ShopTalk: Shaft flex

[Royce Engler]

I've been doing a lot of reading on materials mechanics lately (trying to understand what the hell goes on in a golf swing...), and the following is a summary of a chapter from "The Physics of Golf" by Jorgensen.   Theoretically, the longer shaft is the same flex as the shorter shaft.  It may FEEL softer, but that's not what you are measuring with the frequency analyzer.  The frequency analyzer measures a property of the shaft related to a spring constant of a vibrating rod.  For a given shaft, the frequency that it vibrates when you clamp one end and twang the other is a function of the spring constant (a material property of the shaft commonly called "flex"), the length of the shaft, and the mass of the weight on the end of the shaft (i.e. the clubhead).  For a given flex, and a fixed clubhead weight, increasing the length of the shaft will result in lower frequency.  Likewise, for a fixed length and fixed clubhead weight, a lower "flex" will result in lower frequency.     Think in terms of an FM Precision plot...if you take a shaft, attach a head, measure the frequency, then cut 1/2" off of the length, then repeat the process over and over, you should get a straight line plot of frequency vs. length.  If you match the frequencies of an assortment of shafts that are of equal lengths, then trim them to the lengths you need for the clubs,  and put the same clubhead on each shaft, you will again get a straight line.  If you decrease the clubhead weight by oh, say, 7 grams each as you put them on shorter and shorter shafts, you should again get a straight line, but of a different slope.  The straight lines on the FM Precision plots are based on incremental club weight of 7 grams,  a different increment will change the slope of the line.   In the case you mentioned, there are other factors at work as well.  Increasing the length only will increase the swingweight, which will make it FEEL different.  The stiffness of a shaft can also vary along the length of the shaft, and is a function of the material the shaft is made of, the consistency or homogeneity of the shaft material, the diameter of the shaft, the cross sectional area of the shaft material.  IN GENERAL, the "stiffness" of a shaft is mostly a function of these properties at the tip end and the transition from the gripping area to the tip area (i.e. the so-called bend point).  Depending again on the design of the shaft, it can be made more or less "tip stiff" or "butt stiff".     Does this all make sense? Royce  -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Pat McGoldrick Sent: Wednesday, October 16, 2002 10:28 PM To: [EMAIL PROTECTED] Subject: ShopTalk: Shaft flex Does a 48" long shaft with a 195 gram head play stiffer than a 45" long shaft with the same head? I assume the butt end is the stiffest part of the shaft and whenever you trim the butt end of the shaft, the more flexible the shaft becomes. Is this correct? Then why would the frequency analyzer show the longer shaft with a lower reading?  I have a hard time trying to convince myself of this. Could anyone explain?  Well it's that time for me, be back tomorrow. TIA    Pat McGoldrick On Target Golf