On Thu, October 9, 2003 at 6:34 pm, Dave Tutelman sent the following > At 04:41 PM 10/9/03 -0700, David Rees wrote: >> >> Isn't it possible for a material to have different compression and >> tensile strengths? > > Possible, yes. Does it actually happen? Worth discussing.
<snip> Summary - steel has the same elasticicity in tensile and compressive modulus, graphite is very close to the same </snip> Thanks for validating what I assumed was true, but wasn't sure of. > A few comments: > > (1) You don't need 2-d measurements but they would be interesting, > and for EXACTLY the reason you suggest. The spine and NBP planes will > show all the force in the direction of the bending, and no > perpendicular component. Other planes will show a perpendicular > force, which is why FLO works to find spines and NBPs. Yep. I'm getting the hang of it now. > (2) You need to be careful to measure the DEFLECTION of the shaft, > not the POSITION. That is, you need to measure the DIFFERENCE in > position between zero load and full known load. Even more accurate is > to measure the difference between a small load and a bigger load, > where the load difference is known precisely. If you just measure the > POSITION of the shaft under load, you will still be fooled by shaft > bend, because the starting (no-load) position is different for > different orientations. Isn't that what I said? ;-) > The NF2 does not do difference measurement, so it is fooled by bend. > Dan has designed a way to solve this problem -- a reversible front > bearing -- and I think it is on the NF2 web site. But nobody except > Dan has built one of these. It also involves arithmetic (subtracting > two deflection readings for each shaft position), which has turned > off at least one clubmaker to whom I proposed the solution. (That is, > the solution of an NF2 for difference-deflection measurement to find > the true spine.) He is now using the FlexMaster, which can do the > arithmetic internally. I googled FlexMaster and found some information on it. Seemed like their proponents were intent on bashing frequency analyzers as "old technology", but then go on to say that they double check all their work with one. Seems to me now that you would be able to use either tool effectively, though the only benefit of the FlexMaster is being able to measure how bent the shaft is. But it seems that the bend of the shaft doesn't matter unless it's REALLY bent! > BTW, the difference-deflection measurement is essentially what John > Kaufman did in his testing to show that all shafts are really Type 2. I'll have to go read up on that again. <i'm back> The more I read the more I convince myself that the tried and true method of aligning the N-plane along the target line is the way to go. NBP-CG has still piqued my interest, though. There's a good pic showing the stiffness of your typcial shaft around it's cross-section on John K's site here: http://www.csfa.com/tech35.htm Really helps to visuallize the problem at hand. I wonder if NBP-CG seems to work well because the typical angle of attack of a solid swing is a few degrees in-out and aligning the CG of the head tends to align the NBP very close to this angle (at least in the irons). Thinking about it a bit more, has anyone tried aligning the stiff-plane with the CG? Thanks, -Dave
