Hi Tom, It depends on what theory you believe in. If you believe that a spine finder can find the correct NBP location as I do, then you absolutely can get the NBP exactly at the COG.
Bernie's post on NBP to COG alignment contained a quote from an experimental set I made up. I did not have any high expectations for that set when I made it up. Let me tell you that I was shocked by the difference in the results. The results continue today after months with this set. I continue to hit the best irons of my life. Now this set was a combination of new things for me. First, I used a new shaft, PC Mach 22's, with R+, S- and S shafts in the set. I used my NF2 to tip trim them to a matching profile of .010" deflection between clubs, never having to trim more than 1/2" tip to do so, and the find the NBP locations. Then I made up the clubs with a 3/8" change between lengths, for a poor man's MOI match. Finally I assembled them using the NBP (N1) to COG alignment. It could have any of those factors, or all of them that led to these results, but I was literally shocked by how much better they played than any set I've used. It was the most difference I have seen in at least 10 years of experimenting with clubs, different lengths, different shafts, flexes, torques, components, you name it, I've tried it. I can't ignore results like that, regardless of how tenuous the theory. Dan Neubecker [EMAIL PROTECTED] >-----Original Message----- >From: tflan [mailto:[EMAIL PROTECTED] >Sent: Wednesday, October 08, 2003 12:04 PM >To: [EMAIL PROTECTED] >Subject: Re: ShopTalk: NBP-COG > > >Dr Tutelman: > >A question, por favor. When this subject was broached several >months ago, >and the thread unwound for about 3 weeks, I asked a question >that got no >universally agreed upon answer. The question was; is the spine >found at the >top of the shaft or at the bottom of the shaft when testing in >Dick's spine >finder? Responses were equally, and passionately, divided. > >I then asked another question; if when one finds the spine, >the "hard spot" >via the use of our arguably primitive methods, how can one >accurately mark >and then place the hard spot in a specific position? As I recall, you >responded, correctly, that we'd be lucky to get the spine >situated to within >3 to 4 degrees. You mentioned the circumference of the .335" tip, when >reduced to 360 degrees, would be virtually impossible to set >accurately. I >agree. An assembler would need to identify the spine at the >shaft tip by >marking it with a needle, then mark the hosel in the precise finished >position. Then he'd need to mark the ferrule so the entire >assembly could be >stuck together in one operation. That's nearly impossible given the >workplaces of most assemblers. > >So, this thread re; placing cog/spine in some specific location with >accuracy is theoretically interesting but in practice its pretty much >useless. I'm not knocking anyone, just making a point that's been made >several times in the past. > >TFlan > >----- Original Message ----- >From: "Dave Tutelman" <[EMAIL PROTECTED]> >To: <[EMAIL PROTECTED]> >Sent: Tuesday, October 07, 2003 10:49 AM >Subject: Re: ShopTalk: NBP-COG > > >> A few points I'd like to make concerning things that were >brought up in >> this thread: >> >> (1) As Alan Brooks and John Kaufman and I have said in the >past, every >> shaft will have the stiffest directions (that is, spines) at 180* >> intervals. Similarly with the most flexible directions (that >is, NBP). If >> you measure anything else, there is something wrong with >your measuring >> equipment. (Others have already noted that residual bend >affects a spine >> finder's reading. That is probably the most common thing >that is wrong >with >> your measuring equipment.) >> >> (2) FLO is important!!! It is not important because of >anything the shaft >> may be doing during the swing (unlike a fishing rod), but it >is one of the >> more reliable ways to find the REAL spine, untarnished by things like >> residual bend. In other words, FLO is a more reliable >spine-finder than >> Colin's or Dan's. Slower perhaps, but it finds the real spine. >> >> (3) There are three theories that I have seen about why >spine alignment >> matters. NBP-COG is one of them. Here's the reasoning behind it: >> * At the moment of impact, the major force bending the shaft is >> centrifugal force. (That is probably true, but not >universally accepted. >> But let's proceed on the assumption that it is true.) >> * That force will bend the shaft in the plane of the CG of >the clubhead, >> because centrifugal force acts through the CG of the clubhead. (In >essence, >> it is pulling the CG of the clubhead straight away from the hands.) >> * If the shaft bends in a plane where the forces due to >bending are not >> in the same plane as the bending, there will be spurious >torque on the >> clubhead; you don't want that. >> * But the only planes where the force and the bending are >aligned are >the >> NBP and the spine plane. In other planes, there will be some >small angle >> between the bending and the force in the shaft. So you need >to align one >of >> those planes (either the NBP or the spine) with the CG of >the clubhhead. >> >> (4) If you build your clubs with nearly spineless shafts >(like SK Fiber, >or >> the new Harrisons, or many filament-wound shafts), then it >makes little >> sense to say, "I used NBP-COG alignment [or any other >alignment] and it >> worked GREAT!" You were aligning an effect that probably >didn't matter one >> way or another. >> >> Hope this helps, >> DaveT >
