This time there were at least two. I'm responding here to:
* John Kaufman's statements about spine and bent shafts.
* Charlie Badami's invitation to comment about bent shafts.
* An unspoken but underlying question about NeuFinders as spine finders.
At 09:56 AM 12/24/02 -0600, John Kaufman wrote:
I just stick a shaft in my Club Scout clamp and check the frequency. I then loosen the clamp and rotate the shaft a few degrees. If the frequency goes up I'm moving in the wrong direction so I immediately rotate the shaft in the other direction. I keep doing this until I get FLO in the minimum stiffness (frequency) plane. I don't tweak it forever to get it down to 1 degree alignment. This is the old process of measuring with a micrometer and cutting with an axe.That's a little faster than me. Takes me about a minute. But it gives the REAL spine, not an indeterminate combination of spine and "geometric imperfections". Bernie, when I used that term earlier, bend was uppermost in my mind. But out-of-round will also spoof a bearing-based spine finder. I suspect bend is the most likely culprit, though I'm not sure.
...I took a pretty crummy shaft a few minutes ago and found the plane I was looking for in 15 seconds. It's not a big deal.
And what John says about not needing alignment to a single degree makes a lot of sense.
YES!!!We talk a lot about type 1 shafts, I prefer to just call them bent.
I've been saying this ever since spines were first mentioned on RSG. Probably something like 6 years. I'm delighted to hear another engineer, and a very knowledgeable one, speak up. Hey, Reed, what about you?
My position is that any structural beam (like a golf shaft in bending) is either equally flexible in every direction or has two axes of flat oscillation, a hard one and a soft one. This has the following interesting properties, assuming the tensile and compressive moduli are similar (which they are in shaft materials -- and just about identical in steel):
* The hard and soft planes are at right angles.
* The two planes are the planes of the highest and lowest frequencies that the shaft will vibrate.
* Deflection stiffness is THE SAME IN BOTH DIRECTIONS in each of these two planes.
The last point is the one that says what John just said. If you have an NBP in one plane and no NBP 180* away from it, then you don't have a real NBP. Same for a spine. Every structural design book I've ever seen says so, and it's not hard to derive from the first couple of weeks of any structural engineering course. But it's counter-intuitive to the point of unbelievable for anyone who hasn't gone through such a book or course.
As for empirical evidence, look at the "bow tie" graphs that John plotted in his tech notes, http://www.csfa.com/techframe.htm. These are shafts that looked like type 1 on spine finder and deflection board, but showed behavior consistent with the theory when the differential deflection was measured rather than the absolute deflection. (The differential deflection measures stiffness; the absolute deflection measures stiffness plus bend.)
What I'd like to hear about is some testing that indicates aligning an otherwise very uniform stiffness shaft that is simply bent ( generally all steel shafts) has any effect on the clubs performance. I know of three sets of tests that indicated no effect on performance from alignment of a type 1 shaft but I've not seen any data on tests that indicate alignment did improve performance.That's certainly what I'd expect offhand from the very small out-of-straight of typical commercial shafts. But it's not what Charlie reports in the very next ShopTalk post. And Charlie is an ultimate empiricist with a very sensitive measuring instrument.
At 09:59 AM 12/24/02 -0500, [EMAIL PROTECTED] wrote:
I agree with your descriptions of shaft alignment and the results but as you know no shaft is perfectly straight and that is why I also check the shaft for straightness and align it accordingly. Steve Boccieri is perhaps one of the most knowledgeable people I know of as far as shaft geometry goes and we have been discussing this alignment thing for the past three years and he definitely says that it has effect and was interested in the results of the blind test I had done which had confirmed his suspicions.Double-blind? Definitely not.
Single-blind? Maybe. I didn't see the test. But Charlie is a very expressive individual (I know you won't dispute that, Charlie), and Rich has been working with him for a while. So I'm not at all sure that Rich didn't "know" -- perhaps even subconsciously -- when the club was "supposed" to be good. That why "really blind" means "double blind" in serious human factors experiments.
But Rich is the "sensitive measuring instrument" that Charlie uses to test such things. He can feel differences, or detect them in performance, that I wouldn't expect a golfer to be able to.
Anyway, I don't know how "blind" the test was, nor how consistently the result was duplicated. It was certainly based on only one golfer. So the results are intriguing but not yet conclusive.
I ran into Dave T at the range while working with one of my players and we had the discussion on shaft curve and I know he will be able to explain it better than I. Arnie, about your comment on shaft manipulation, Rich hits a predominate straight ball although he is able to work the ball both ways on command, when I see a club continuously leave the ball hanging in one direction or another I believe that the shaft is not in a neutral position and am looking to place that shaft as neutral as I can so that he can do whatever he deems is necessary for each particular shot.We really did just "run into one another at the range". And it's a public range, not a private club where you expect to see your friends. (BTW, that suggests that we're enjoying plausible weather for late December in NJ. We are; I golfed twice in the last 5 days. Well, I went out with clubs on the course anyway. It's artistic license to call it golf. :-)
The "neutral position" makes a certain amount of sense, if you assume that small a bend has any effect at all. I wouldn't have guessed it, but Rich claims to feel it. My explanation below is based on intuition, and a mental exaggeration of the bend to something much larger. Since we all know by now how misleading intuition can be when discussing golf physics (for instance, see "Type 1 = bent" discussion above), let's not assume this is actually correct, but rather just a first hypothesis:
The most violent motions of the clubhead during the downswing occur in the last fraction of a second (probably about 50 milliseconds) before impact. Particularly in a good swing, the clubhead is "releasing"... that is, it is actually pulling the shaft into a forward bend. The wrist usually can't uncock fast enough to keep up, so a light grip does the least damage. So let's look at what is probably happening during this critical period. And we'll imagine a seriously bent shaft, just so we can visualize it more easily. Unfortunately, the actual effect with a small bend may be qualitatively different. Also, this argument doesn't quantify the effect enough to know if anybody -- or maybe anybody but Rich -- is affected by the actual bend one experiences in real shafts.
Late during this release time, when the clubface is square to the ball, the bend may be described on the clockface for a right-handed golfer, as we often do when talking about spines. Let's look at the cardinal points of the clock for bend:
12 o'clock: clubhead wants to pull the face shut.
3 o'clock: clubhead is unstable; might "jump" either way.
6 o'clock: clubhead wants to pull the face open.
9 o'clock: clubhead wants to pull the face straight ahead, square.
I'm pretty sure Charlie said he found that the 9 o'clock position was the "neutral" one. This agrees with the hand-waving I've done above -- and it is still in the realm of hand-waving as far as I'm concerned. We didn't have time to discuss the specific results of the other compass points; Charlie, does the explanation correctly predict what you observed?
One last comment. (BTW, I hope that NeuFinder discussion groupies are also ShopTalkers, because I'm not cross-posting this.)
The discussion above about bent shafts strongly suggests that the NeuFinder does not find a true spine as a spine-finder, but is spoofed by geometry. I believe that to be completely true. But you CAN use a NeuFinder as a spine-finder if you do it right. Unfortunately, this process is more tedious than what Bernie and John and I attribute to finding spines with a frequency analyzer.
You have to find NOT the direction of minimum dial reading, but minimum difference in dial reading for a known change in deflection. That means you have to take two dial readings at each interesting rotation, and compute the difference in readings. The direction with the smallest difference is the NBP.
John explains in his tech notes how he did this with a V-block added to his inverted flex board. Dan has designed a reversible bearing to to the same thing more conveniently. I'm sure he'll post it if there is enough interest in going to this precision.
Have a happy holiday, all!
DaveT
