On Thu, October 9, 2003 at 2:23 pm, Dave Tutelman sent the following > > SPINE is the stiffest plane of a shaft in bending. NBP is the most > flexible plane. The concept of plane is the first area of > disagreement among the protagonists. Some say that it is possible for > the stiff side to be 180* opposite the flexy side. But the engineers > in the group say that is not so; it is an artifact of an imperfect > instrument used to find the spine. In fact, spines will be 180* apart > every time, hence I talk about "plane". Similarly NBPs will be 180* > apart from one another every time. BTW, that is what John Kaufman > proved. He proved nothing about how to align the spine or NBP when > you make a club, just that the order of things as you go around the > shaft is spine-NBP-spine-NBP at about 90* intervals. This also agrees > with: * Theory that every mechanical and structural engineer learns > in school. * Tests that others have done, including one I've > witnessed involving a FlexMaster.
Not being a mechanical or structural engine who is familiar with the tensile properties of the materials used in golf shafts, I may be way off base here, but here goes: Isn't it possible for a material to have different compression and tensile strengths? For example, we'll use some poor ascii art below depicting a side view of a shaft where one side of the shaft is significantly thicker than the other: -------------------------------- ================================ The top side drawn with the - is the thin side, the bottom side drawn with the = is the thick side. Assume (which is probably a bad assumption but will get the point across) that the material does not compress at all, but does stretch linearly depending on the thickness of the material. If you pull down on the shaft the club will deflect some amount. But if you push up on the shaft the club will only deflect 1/2 the amount as it deflected down. Measured in a frequency meter you will only get one reading as a frequency meter can only measure stiffness in planes, but in a deflection meter you will find the shaft bends different amounts in each direction obviously affecting the position you might want to orient the shaft. It also seems that if the shaft started off bent in one direction or the other, it would affect the stiffness of the shaft in each direction. How much? I don't know, you guys who know materials better than can will probably tell me what I've described isn't possible. ;-) Please do if I'm totally off base. So from what I can tell, the main drawback of a frequency meter is that you can only measure stiffness in planes, when a shaft may actually have a different stiffness in each direction. The main drawback of your typical spine finder (don't know if this applies to the NF2 or not) is that you don't take into account any bend of the shaft. It seems to me that a method which could be used to measure the stiffness of a shaft would be done as follows: Clamp one end of the shaft in a bearing device with no load on the other end. Take 2-d deflection measurements at multiple points around the shaft, making sure that each measurement is made using a constant force. An easy way would be to use a weight free hanging to prevent side-forces from affecting measurements. 2-d measurements may not be necessary if shafts always bend in the vertical plane, but I think if they did, you would always get FLO no matter which way you aligned a shaft. Once you've got this data, you will be able to predict what direction the shaft will flex and how much based on the weight used. The tricky part will then to use that data to align the shaft in the position which most consistently returns the clubhead to the spot the golfer expects it to. I think Dan's NF2 can do all these types of measurements but the 2-d measurements, maybe it can be easily adapted to make 2-d deflection measurements as well. -Dave
