When Tom Mace left the industry to go back to the academic world at Cal Poly SLO, I had him do a complete full out EI of multiples of all my shaft designs and flexes so I would be able to compare the EI curves to see their relationship to our Bend Profile software's progressive beam length frequency graphs. While the shape and orientation of the EI curves were different, in relation to each other by each different shaft, they were the same as what we output in our bend profile measurement work. I've always agreed that our BP measurements were NOT actual stiffness measurement, but with this correlation check to EI, I am satisfied they are valid for shaft to shaft comparison of relative stiffness differences in shafts.
TOM -----Original Message----- From: owner-shopt...@mail.msen.com [mailto:owner-shopt...@mail.msen.com] On Behalf Of Dave Tutelman Sent: Thursday, June 04, 2009 9:00 AM To: ShopTalk@mail.msen.com Subject: Re: ShopTalk: Flex Board At 10:10 AM 6/4/2009, john wrote: Hi Dave, Once upon a time I ran a frequency profile of a shaft and then ran force/deflection profile of the same shaft just to see what I would get. I ran the deflection (actually I did differential deflection) as I shortened the beam length exactly as I had done with the frequency profile (the Wishon/kaufman/Hoefling/PCS approach). The plots looked remarkably similar. OF COURSE THEY DO! I said so in both my articles on profiling (< http://www.tutelman.com/golf/shafts/profiling.php> and < http://www.tutelman.com/golf/shafts/profiling2_plot.php>). The issue here is NOT frequency vs deflection. It is HOW you vary the clamp and the load to do the profiling. For instance, there is a frequency analogy to method #2 (appended below for context). Imagine a fixed clamp at the butt of the shaft, and a weight that can slide to different stations when you take the frequency. That would produce a plot that looked like the deflection plot of #2. Both of the above plots, deflection and frequency, look very different from either a Wishon/Kaufman/Hoefling/PCS plot or an NF-4 plot. Which, as we both know, do look like one another if the beam length is suitably interpreted. Whether it's frequency or deflection, the most accurate way to do profiling is to load the tip, and clamp off the beam length at varying distances from the tip. That was the point of my post. Cheers! DaveT From: "Dave Tutelman" <dtutel...@optonline.net> Sent: Thursday, June 04, 2009 8:27 AM To: ShopTalk@mail.msen.com Subject: Re: ShopTalk: Flex Board I'd like to point out a few things about profiling here: (1) A flex board IS a profiler. Inherently! Put a weight on the tip, let it settle, and plot the deflection of the shaft at 5" (or 1" if you prefer) intervals. That is the purest form of profile, in that it shows the deflection along the length of a tip-loaded shaft gripped at the butt -- as happens in the swing. True, that particular graph bears no resemblance to a Wishon-style frequency plot or an NF-4 plot (which, by the way, are closely related to one another). But then, neither does an EI plot. Each has its own uses and its own devotees. And they CAN be converted, one to another -- though you need computer cycles to do so. (2) Andre's suggestion of clamping the butt and sliding a weight is also not related to the more common frequency or NF-4 profile plots. The more common plots load the tip and slide the clamp; the graph and what it tells you is quite different. (3) A study by Brillouette (Science and Golf IV) examined all three methods: #1 above, #2 above, and the more common frequency or NF-4 approach (tip load, sliding clamp). He started from the assumption that the goal of profiling is to determine the local stiffness (in other words, the EI) at each point along the shaft. #1 and #2 were found to be rather inaccurate, except close to the butt. The usual approach did much better over the length of the shaft, including near the tip. If you believe this, and I do, then the best way to make a flex board into a profiler is to open the end of the butt support so the shaft can slide, and keep the weight at the tip. (4) I don't know how to evaluate Andre's most recent suggestion: support butt and tip, and slide a weight. What measurement do you take? Deflection at the weight? A full deflection plot (like #1) for each position of the weight? I'm sure the latter would give more accurate results (as I understand the Brillouette study). I'm not sure what the former would tell you. (5) Finally, none of this tells you how to implement "differential deflection", which you need in order to compensate for things like the shaft's diameter profile and any residual bend of the shaft. You would have to measure the deflection both before and after the weight is applied, and use the difference. Hope this puts it to rest. DaveT -- Shoptalk ** Sponsored by the new Aldila Voodoo. Learn more at http://aldilavoodoo.com/
