Questions about SW and MOI.

[Fade]

I have some curiosity about the swing-weight (SW) and moment of inertia (MOI) of golf-clubs, and the way they are typically defined:

 

What justifies the position of the fulcrum (typically 14" from the butt of the club) on the SW-scale?

 

What justifies the position of the axis of rotation (typically at the butt of the club) for the MOI measurement?

 

In both cases, my question basically is: Why there?

[Stuart_G]

Good question.

I'm no expert on the history of how the SW measurement came to be but my understanding is that it was determined from a "trial and error" approach to find that 14" point. Possibly a reversed engineering approach that started with set that was considered a 'good' match and experimenting with different measuring balance points (and possibly methods) that quantitatively showed they did in fact match. That could be just supposition. I do know, at one point there were also different SW scales that used 12" fulcrums so I assume there was some contention (or refinement) about where that point really should be. For whatever reason (whether actually more helpful or better marketing or something else), the 14" scale "won out" in the long term.

[Stuart_G]

Sorry one other thing. I suspect Fade might know this but for others. If you are wondering why the SW balance point was moved away from what is "obviously" the point around which the club really rotates during the swing and down toward the head of the club, it was because it was an attempt to try and come close to an MOI based representation in a much simpler and easier to use balance based mechanism. It's not that they didn't know about MOI back then, it's just that it wasn't something that was easy or possibly just not convenient to measure (it's still not really convenient or requires expensive gear). MOI is calculated based on length squared while balance is just a function of length to the first power. By moving the fulcrum point toward the head, you increase the contribution of the head weight to the result in a balance measurement (hopefully) in a "close enough" manner to what happens with an MOI based measurement. The question then becomes how far to move it to see results that are somewhat similar to MOI matching - which brings us back to the original question.

[Fade]

[quote name='Stuart G.' timestamp='1427274036' post='11211305']
Good question. [/quote]

Great answers. Thank you.

I was trying to find some theoretical reason for the 14" fulcrum of the swing-weight scale, and was not able to come up with one, but I can believe that the swing-weight scale is a rather practical solution for club-makers trying to provide a set of clubs that feel like they match when swung.

[Stuart_G]

No problem. Interesting read here on the history of the SW scale. Most likely the original source for my answers even if I didn't recall the source when I wrote the answer. If I had remembered, I would have just posted the link instead of doing all that typing :-) A bit more interesting info on the 12" vs 14" SW scales.

[url="http://www.tutelman.com/golf/design/swingwt1.php"]http://www.tutelman....gn/swingwt1.php[/url]

[Fade]

I will repeat, then (hopefully) clarify my second question:

[i]What justifies the position of the axis of rotation (typically at the butt of the club) for the [color=#FF0000][background=rgb(255, 255, 0)]MOI[/background][/color] measurement? (Why there?)[/i]

The axis of rotation for MOI measurement/adjustment is typically chosen as the butt-end of the club. Together with the goal of MOI matching (to make all clubs feel the same when swung), this suggests that the cub is swung on a circle with the butt-end of the club as its center and the length of the club as its radius. This is obviously not the case throughout the entire swing, but is this somehow valid for the most important part of the swing?

[Stuart_G]

That one I'm leaving to Tom (or someone else more knowledgeable with the history of MOI matching than I am). I've asked myself the same question but never found any references with an answer. Swing mechanics analysis does say the rotation point is at the hands but I don't recall seeing anything that gets more specific for a location than that. I would have guessed at least a few inches down would have been more accurate representation of the actual rotation axis but can only (again, another complete guess) consider that maybe the exact axis used (from the stand point of club matching, not absolute MOI values) is not enough to worry about.

[TomWishon]

[quote name='Fade' timestamp='1427248210' post='11209811']
I have some curiosity about the swing-weight (SW) and moment of inertia (MOI) of golf-clubs, and the way they are typically defined:

What justifies the position of the fulcrum (typically 14" from the butt of the club) on the SW-scale?

What justifies the position of the axis of rotation (typically at the butt of the club) for the MOI measurement?

In both cases, my question basically is: Why there?
[/quote]

I can answer this for you because I was the guy who in combination with my engineering mentor/teacher in the early 2000s developed the concepts and the equipment with which to measure the MOI of golf clubs and perform MOI matching as an alternative to swingweight.

As to your first question about the 14" fulcrum on a swingweight scale, this most definitely was an arbitrary decision made after experimentation with several other means to measure the relationship between headweight and the overall weight/length of the club. I even have an old swingweight scale in my collection of stuff marked in A, D, C, D increments that had its fulcrum placed at the end of the grip. Credit for the development of the 14" fulcrum swingweight scale is given to a Robert Adams of Woburn, Mass, who simply was a "tinkerer" and came up with the 14" fulcrum after experimentation with other forms of head weight to club weight and length measurement. Why this 14" scale took off and was embraced by the golf companies from then on is not known for sure and open to speculation. More than likely this happened simply because Adams took the time to manufacture his scale in the form of a very professional looking piece of equipment which attracted the attention of the golf companies who at the time were open to having a means to set up the head weight relationship of their clubs for a standardized form of measurement.

As to the choice of the MOI being defined about the axis of the end of the club, when we were first working on coming up with a means to do MOI measurement and matching of clubs, we very much did look into two different axes of rotation. We considered the spine at the base of the neck as the axis of rotation for MOI measurement because golfers do make their swing by rotating about the spine. So this very much was a viable axis of rotation for the MOI.

But we decided to go with the end of the grip as the axis of rotation for our MOI measurement work because we considered the release of the club as being very important to the execution of the shot and the delivery of the club to impact. It is the release that triggers the achievement of the golfer's maximum possible clubhead speed and it is the release that has a great deal to do with the face angle and the angle of attack of the club coming into the ball.

Again, we could have chosen the spine axis, but when all things were considered we just felt for being able to define the MOI for the purposes of achieving a similar swing feel for all clubs in a set, the release was more appropriate to that goal.

As to why the very end of the grip for the axis of rotation and not an area on the grip between the two hands, we chose the end of the grip because this really is the pivot point or axis in the release as per the wrist of the upper hand in the grip. Both hands are together on the grip during the swing as ONE UNIT. There is no flexing between the two hands on the grip because the rigidity of the shaft and grip prevent that. So when the golfer releases the club, the "hinge" is really at the wrist of the upper hand. And thus it just made more sense to define the end of the grip as the axis of rotation for the MOI of the club in our goal to find a different and potentially better way to duplicate swing feel of the clubs - or rather to be able to say that the MOI of the club controlled the effort required by the golfer to release the club to impact.

Hope this helps

[Fade]

[quote name='TomWishon' timestamp='1427294765' post='11212445']Hope this helps[/quote]

It certainly does. Thank you for your elaborate reply. Before reading your reply and Tutelman's page that Stuart linked to, I hadn't considered separating the release action from the rest of the swing (instead I had been thinking that the overall motion of the club would be be more important). This gives me a lot of food for thought. I love the idea of a matched set and this may go quite a way towards me buying into the idea. And I am looking forward to going to the range to find out if I can feel the swing (or release) of the club the way you explain it.

[TomWishon]

[quote name='Fade' timestamp='1427332442' post='11216941']
[quote name='TomWishon' timestamp='1427294765' post='11212445']Hope this helps[/quote]

It certainly does. Thank you for your elaborate reply. Before reading your reply and Tutelman's page that Stuart linked to, I hadn't considered separating the release action from the rest of the swing (instead I had been thinking that the overall motion of the club would be be more important). This gives me a lot of food for thought. I love the idea of a matched set and this may go quite a way towards me buying into the idea. And I am looking forward to going to the range to find out if I can feel the swing (or release) of the club the way you explain it.
[/quote]

Please do understand that there are most definitely compelling arguments for setting up an MOI Match about the spine axis. No question about that. In a perfect world, we would have created both methods, put them both out there for long term testing, and watched what happened. But we couldn't do that for various reasons, not the least of which would be confusion among clubmakers and among golfers. And the surest way to kill something new that is flying in the face of 90 yrs of swingweight matching use would be to introduce a new way to match clubs that brings a level of confusion right from the get go.

So we felt we had to decide on one method and our thought process and experience led us to go in the direction of the MOI match about the axis of the release.

One also must keep in mind that there are a number of other issues all related to a goal of trying to make all clubs in the set demonstrate the same exact swing feel to try to offer an improvement in swing and shot consistency among all clubs in the set. Truthfully, if one wants each club to duplicate every possible swing feel factor imaginable, the only way to do that currently is to make all clubs in the set to have the same length, same total weight, same headweight, same balance point, same exact shaft stiffness, same lie to ensure the same stance and posture, etc, the same everything.

But at this point in the game, single length sets are a little bit outside the realm of acceptability for the majority of golfers because the concept of incremental length clubs is just so completely predominant. Not to mention the fact that single length clubs bring with them another set of challenges to have to be overcome to make such a set really work as well as a perfectly fit set of incremental length clubs. Not insurmountable by any means, but a definite challenge.

So for us, when we wanted to dig into a different way to go about trying to improve the concept of making the clubs in a set to have a BETTER swing feel consistency than swingweight matched clubs, MOI Matching was the way to do this. Because the whole concept behind MOI matching is the fact that when the MOI is matched, this means each club requires the same effort to swing the club ABOUT ITS AXIS OF ROTATION. BUt we also felt that our work in pioineering MOI matching of clubs had to be done within the norm of sets in which the clubs were made to different lengths because that is just such a predominant manner of making clubs in a set.

Therefore, that does not mean every club will swing with precisely EVERY SINGLE ASPECT OF FEEL because when you do make clubs to different incremental lengths in a set, you do bring about the fact that even in an MOI Matched set, the clubs still are of different total weights, different lies and a little different balance point. But no question, MOI matched clubs DO swing in a way that requires the golfer to use the same exact amount of effort to swing the clubs about its defined axis of rotation.

Could there be other ways to make clubs in a set so they can still be of different incremental lengths and demonstrate more of the duplicatible swing feel factors? Probably. Possibly by different weights put in different areas of the shaft. But that brings with it another set of challenges not the least of which would be how would you put weights in different areas of the shafts that all can have different inside core diameters, as well as the calculations to know how much weight, and where in each shaft, and all that.

Anyway, just some more fodder for the discussion there. . . . .

At least we do know that from 12 yrs now of monitoring and listening to clubmakers' experiences from now thousands and thousands of MOI match jobs for golfers, we do feel pretty good that this current form of MOI matching is superior to swingweight matching for being able to offer little improvements in swing consistency, shot consistency.

And we or someone else will move it on from there to a next level of improvement over the next several years, perhaps.

[Fade]

[quote name='TomWishon' timestamp='1427380956' post='11219851']Anyway, just some more fodder for the discussion there. . . . .
[/quote]

I [b]really [/b]appreciate how much you are willing to share in this thread. Thank you again. It has provoked some thoughts of my own, but I won't be able to write them up until this weekend.

[weihiluo]

Where MOI is concerned, it simply does not matter where you choose the standard.
This is because of the fact that if you know the MOI of a body about an axis, you can calculate its MOI about any axis parallel to the one you know.
This is known as the parallel axis theorem:
http://en.wikipedia.org/wiki/Parallel_axis_theorem

So, there are are some obvious axes to choose: center of mass, grip end of club, head end of club, etc.
I think the choice of grip end is the best choice as it is the one that is physically easiest to realize.
That is to say, it is simplest to build a jig that holds clubs by the grip and align with the end of the grip in the same place each time.

But, the reality is the choice does not matter.
You can transform your number to any reference point you like with a simple calculation.
It is a lucky mathematical accident of the definition of MOI.

[Fade]

[quote name='weihiluo' timestamp='1427431248' post='11225551']
Where MOI is concerned, it simply does not matter where you choose the standard.
This is because of the fact that if you know the MOI of a body about an axis, you can calculate its MOI about any axis parallel to the one you know.
This is known as the parallel axis theorem:
[url="http://en.wikipedia.org/wiki/Parallel_axis_theorem"]http://en.wikipedia....el_axis_theorem[/url]
[/quote]

The context of this thread is choosing the proper axis, so that - for example - in a set of 8 irons of identical MOI, all irons require the same effort to swing (or release). For that reason, the location of the axis must be appropriate for the swing (or release) motion.

[Fade]

[quote name='TomWishon' timestamp='1427294765' post='11212445']
As to why the very end of the grip for the axis of rotation and not an area on the grip between the two hands, we chose the end of the grip because this really is the pivot point or axis in the release as per the wrist of the upper hand in the grip. Both hands are together on the grip during the swing as ONE UNIT. There is no flexing between the two hands on the grip because the rigidity of the shaft and grip prevent that. So when the golfer releases the club, the "hinge" is really at the wrist of the upper hand. And thus it just made more sense to define the end of the grip as the axis of rotation for the MOI of the club in our goal to find a different and potentially better way to duplicate swing feel of the clubs - or rather to be able to say that the MOI of the club controlled the effort required by the golfer to release the club to impact.
[/quote]

I am not saying that the choice of the axis of rotation at the butt-end of the grip (/ at the wrist of the upper hand) was unwise, but I think some of the assertions in the above quote are worded too strongly and not entirely logical. Some golfers might release the club with both hands working to manipulate the club around an axis located between their hands: The rigidity of the shaft does nothing to prevent this, in fact it makes this possible, and the human body is certainly capable of performing the action. Perhaps this would not be the best use of the golfer's body to move the club, but it is certainly possible to do so.

[Fade]

[quote name='TomWishon' timestamp='1427380956' post='11219851']
Please do understand that there are most definitely compelling arguments for setting up an MOI Match about the spine axis. No question about that. In a perfect world, we would have created both methods, put them both out there for long term testing, and watched what happened. But we couldn't do that for various reasons, not the least of which would be confusion among club-makers and among golfers. And the surest way to kill something new that is flying in the face of 90 yrs of swingweight matching use would be to introduce a new way to match clubs that brings a level of confusion right from the get go.

So we felt we had to decide on one method and our thought process and experience led us to go in the direction of the MOI match about the axis of the release.[/quote]

Yes, I can see how different golfers will perform and feel their swings differently, and how in an ideal world they might be fitted for the axis of rotation most appropriate for them. It would be pretty damned difficult to get that judgment right though, and it would complicate the work on the clubs and equipment needed to provide the match as well. Your approach to keep it simple, your focus on the release, and your choice for the position of axis of the release all seem very reasonable.

However, since I personally had trouble seeing the reasons behind the current choice of MOI axis, and the focus on the release action, I wonder whether the word "swing" should be avoided when talking about the current method of MOI-matching, it sure seems to have led me in the wrong direction when thinking about this. Therefore, I am tempted to think that golfers might benefit from the following minimal 'instruction manual' for using their MOI matched clubs, that emphasizes the word "release" instead:

[i]Congratulations. You are now the owner of a MOI-matched set of clubs. The axis of rotation of MOI was chosen as the butt-end of the grip (at the wrist hinge of the upper hand). If these clubs are released around this axis, the release action will require the same amount of effort for each club, thus feel the same, thereby promoting consistent performance throughout the set.[/i]

Heck, this might even improve golfers' technique!

[Largechris1]

[quote name='Fade' timestamp='1427651540' post='11240165']
[quote name='TomWishon' timestamp='1427380956' post='11219851']
Please do understand that there are most definitely compelling arguments for setting up an MOI Match about the spine axis. No question about that. In a perfect world, we would have created both methods, put them both out there for long term testing, and watched what happened. But we couldn't do that for various reasons, not the least of which would be confusion among club-makers and among golfers. And the surest way to kill something new that is flying in the face of 90 yrs of swingweight matching use would be to introduce a new way to match clubs that brings a level of confusion right from the get go.

So we felt we had to decide on one method and our thought process and experience led us to go in the direction of the MOI match about the axis of the release.[/quote]

Yes, I can see how different golfers will perform and feel their swings differently, and how in an ideal world they might be fitted for the axis of rotation most appropriate for them. It would be pretty damned difficult to get that judgment right though, and it would complicate the work on the clubs and equipment needed to provide the match as well. Your approach to keep it simple, your focus on the release, and your choice for the position of axis of the release all seem very reasonable.

However, since I personally had trouble seeing the reasons behind the current choice of MOI axis, and the focus on the release action, I wonder whether the word "swing" should be avoided when talking about the current method of MOI-matching, it sure seems to have led me in the wrong direction when thinking about this. Therefore, I am tempted to think that golfers might benefit from the following minimal 'instruction manual' for using their MOI matched clubs, that emphasizes the word "release" instead:

[i]Congratulations. You are now the owner of a MOI-matched set of clubs. The axis of rotation of MOI was chosen as the butt-end of the grip (at the wrist hinge of the upper hand). If these clubs are released around this axis, the release action will require the same amount of effort for each club, thus feel the same, thereby promoting consistent performance throughout the set.[/i]

Heck, this might even improve golfers' technique!
[/quote]

I asked the same question as OP to Dave Tutelman 3 years ago - he kindly replied that the fulcrum varied through the swing, the centre of rotation could arguably be taken as 12 inches above the butt of the shaft, or lower down the grip, depending on your interpretation of high speed photography of shaft positions and where the most important 'feel' elements were in the swing.

He advised checking out the book 'physics of golf' by Jorgensen that includes a method of perfectly matching irons with weights mounted both in the head and mid way down the shaft., as per Tom describes above. I would like to build a set that way sometime, but boy the mathematics are complicated.

[@@@]

Great thread, got me thinking I wonder if anyone has done any type of fitting based on the balance point of the club. ie if 2 clubs have the same total weight but one is more in the head vs the grip and shaft that would obviously have an effect on swingweight and MOI. It would be interesting to see how matching balance points across assembled clubs effects feel and consistency and I suppose across different lengths whether a match relative to the head or butt or % across length felt more consistent

[TomWishon]

[quote name='Fade' timestamp='1427651540' post='11240165']


Yes, I can see how different golfers will perform and feel their swings differently, and how in an ideal world they might be fitted for the axis of rotation most appropriate for them. It would be pretty damned difficult to get that judgment right though, and it would complicate the work on the clubs and equipment needed to provide the match as well. Your approach to keep it simple, your focus on the release, and your choice for the position of axis of the release all seem very reasonable.

However, since I personally had trouble seeing the reasons behind the current choice of MOI axis, and the focus on the release action, I wonder whether the word "swing" should be avoided when talking about the current method of MOI-matching, it sure seems to have led me in the wrong direction when thinking about this. Therefore, I am tempted to think that golfers might benefit from the following minimal 'instruction manual' for using their MOI matched clubs, that emphasizes the word "release" instead:

[i]Congratulations. You are now the owner of a MOI-matched set of clubs. The axis of rotation of MOI was chosen as the butt-end of the grip (at the wrist hinge of the upper hand). If these clubs are released around this axis, the release action will require the same amount of effort for each club, thus feel the same, thereby promoting consistent performance throughout the set.[/i]

Heck, this might even improve golfers' technique!
[/quote]

The terminology we use in our explanations of what MOI matching is and what it may help a golfer to achieve is to say that MOI matched clubs allow the golfer to use the same [b]effort[/b] to swing the club to impact. Yes we use the word "swing" but the focus is really on this matter of the clubs requiring the same effort because scientifically that is what MOI matching is all about. If the MOI is the same, then under the science of what MOI is, they do require the same effort, but as you say specifically, same effort to release the club.

At any rate, I guess what may be more pertinent for me to say is that after reflecting on the years of feedback from clubmakers who have been using MOI matching as an alternative to swingweight in all their fitting work as well as from golfers who have had it done to their clubs, overwhelmingly the consensus is positive. No, it's not more important than getting any of the other key fitting specs like length, shaft, total weight, lie, etc., right for the golfer. When custom fitting results in definite improvement for the golfer, MOI matching is one part of the whole fitting experience. Is it the most important? For some it might be, for others perhaps getting a better length, shaft, total weight, lie, etc. could be key because one or more of these were badly fit to them previously.

But my point is that with the positive reports we have gotten since we introduced MOI matching to the clubmakers in late 2003, far more seem to think it is a little bit to a lot better than who do not. One clubmaker from England who is in the top 5 in the world in fitting knowledge/experience IMO and who has done this exclusively on the clubs he has fit and sold since 2004 has told me that since then, he has had one golfer come back to have his clubs switched back to a swingweight match. None of the others he has fit in the last 11 yrs have switched back. So regardless of the axis of rotation we declared for our work in MOI matching, it seems to be worth thinking about doing for assisting in swing consistency, on center hit consistency, swing repeatibility.

[T.Beau]

[quote name='TomWishon' timestamp='1427735201' post='11245879']
[quote name='Fade' timestamp='1427651540' post='11240165']
Yes, I can see how different golfers will perform and feel their swings differently, and how in an ideal world they might be fitted for the axis of rotation most appropriate for them. It would be pretty damned difficult to get that judgment right though, and it would complicate the work on the clubs and equipment needed to provide the match as well. Your approach to keep it simple, your focus on the release, and your choice for the position of axis of the release all seem very reasonable.

However, since I personally had trouble seeing the reasons behind the current choice of MOI axis, and the focus on the release action, I wonder whether the word "swing" should be avoided when talking about the current method of MOI-matching, it sure seems to have led me in the wrong direction when thinking about this. Therefore, I am tempted to think that golfers might benefit from the following minimal 'instruction manual' for using their MOI matched clubs, that emphasizes the word "release" instead:

[i]Congratulations. You are now the owner of a MOI-matched set of clubs. The axis of rotation of MOI was chosen as the butt-end of the grip (at the wrist hinge of the upper hand). If these clubs are released around this axis, the release action will require the same amount of effort for each club, thus feel the same, thereby promoting consistent performance throughout the set.[/i]

Heck, this might even improve golfers' technique!
[/quote]

The terminology we use in our explanations of what MOI matching is and what it may help a golfer to achieve is to say that MOI matched clubs allow the golfer to use the same [b]effort[/b] to swing the club to impact. Yes we use the word "swing" but the focus is really on this matter of the clubs requiring the same effort because scientifically that is what MOI matching is all about. If the MOI is the same, then under the science of what MOI is, they do require the same effort, but as you say specifically, same effort to release the club.

At any rate, I guess what may be more pertinent for me to say is that after reflecting on the years of feedback from clubmakers who have been using MOI matching as an alternative to swingweight in all their fitting work as well as from golfers who have had it done to their clubs, overwhelmingly the consensus is positive. No, it's not more important than getting any of the other key fitting specs like length, shaft, total weight, lie, etc., right for the golfer. When custom fitting results in definite improvement for the golfer, MOI matching is one part of the whole fitting experience. Is it the most important? For some it might be, for others perhaps getting a better length, shaft, total weight, lie, etc. could be key because one or more of these were badly fit to them previously.

But my point is that with the positive reports we have gotten since we introduced MOI matching to the clubmakers in late 2003, far more seem to think it is a little bit to a lot better than who do not. One clubmaker from England who is in the top 5 in the world in fitting knowledge/experience IMO and who has done this exclusively on the clubs he has fit and sold since 2004 has told me that since then, he has had one golfer come back to have his clubs switched back to a swingweight match. None of the others he has fit in the last 11 yrs have switched back. So regardless of the axis of rotation we declared for our work in MOI matching, it seems to be worth thinking about doing for assisting in swing consistency, on center hit consistency, swing repeatibility.
[/quote]

Hi Tom,
i can see where MOI matching can be relevant if you are matching a set of irons. but what about the woods? wedges? wedges are often swung in diff manners and at diff speeds, and woods are woods...they are pretty much longer than the irons so i think that would bring other dynamics into play. also the sizes and shapes and balances are all different. so do you try and match everything up, or just match the irons, or match woods to woods?
in tennis swingweight is your version of moi matching. a racquet is mounted on a rdc machine and is swung on a horizontal axis which produces a numeric output. it's pretty revealing until you are trying to match say 6 frames for an advanced player and then it becomes pretty convoluted and not of much value even though the length of all the racquets are identical. you could have 6 racquets of identical swingweight which perform and feel quite differently (depending upon a players sensitivity to specs).

what really helps is if the racquets arrive w. tight tolerances to begin with..makes matching much easier and more successful. to that end, i bet your stuff comes to you w. tighter tolerances than the hugely mass produced stuff. i would think head specs being on target is most impt since the head is located at the end of the stick

i know that moi is also measured for hockey sticks.....and i bet for baseball bats, and who knows what else in the world of sports

[TomWishon]

[quote name='T.Beau' timestamp='1427738181' post='11246243']

i can see where MOI matching can be relevant if you are matching a set of irons. but what about the woods? wedges? wedges are often swung in diff manners and at diff speeds, and woods are woods...they are pretty much longer than the irons so i think that would bring other dynamics into play. also the sizes and shapes and balances are all different. so do you try and match everything up, or just match the irons, or match woods to woods?
in tennis swingweight is your version of moi matching. a racquet is mounted on a rdc machine and is swung on a horizontal axis which produces a numeric output. it's pretty revealing until you are trying to match say 6 frames for an advanced player and then it becomes pretty convoluted and not of much value even though the length of all the racquets are identical. you could have 6 racquets of identical swingweight which perform and feel quite differently (depending upon a players sensitivity to specs).

what really helps is if the racquets arrive w. tight tolerances to begin with..makes matching much easier and more successful. to that end, i bet your stuff comes to you w. tighter tolerances than the hugely mass produced stuff. i would think head specs being on target is most impt since the head is located at the end of the stick

i know that moi is also measured for hockey sticks.....and i bet for baseball bats, and who knows what else in the world of sports
[/quote]

I am aware that there has been a device for swingweight measurement on rackets for some time. I don;t watch it much, but I do see that one of the industry's leading clubmaking machinery makers, golfmechanix.com, does make a new form of such a machine for rackets. I also have spoken with guys who are in the hockey stick and bat business and am aware that they too pursue a form of MOI measurement and fitting their participants to a specific MOI. Haven't spoken to them to the point to ask about specifics on that though as I do not have that close of contact with those guys in my day to day doings.

I do recall way back in the early to mid 90s when driver heads compression molded from graphite had a few years of popularity, one factory I worked with that made our comp molded graphite heads was chiefly a racket maker because the process for manufacturing rackets was also compression molding. I visited this factory on one of my many trips over to Taiwan at the time and had the chance to see the complete process of racket production. This factory was a major supplier to Wilson for rackets at the time and in fact when I was there, they were finishing up a big number of rackets that they had made for Pete Sampras. I forget the model name of the racket but they were finished in a cobalt blue paint, in case you may remember which one it was from that era.

Anyway, my point in mentioning that is the fact that from what you say about racket variations in weight distribution, I can now relate to what you say. One of the big things that struck me in watching them mold the frames that seemed "odd" was how they just "crammed" the sheets of the composite pre preg into the molds. In other words, it did not seem to me at the time that things were all that precise in other words. Not precise in the sense of how precise graphite shaft makers are to very carefully cut identical sheets of pre preg for each shaft design for each wrap step in the procedure.

I certainly try to keep tolerances as tight as I can on the heads I design. Most of that in our business is determined by what factories you choose to work with, AND how much you prove to them that you are watching specs on each production run. The better head making factories most definitely have tighter tolerances built into their production procedures, machinery, worker training, etc. And for this, you pay more because it costs them more to do all those things. It also is good to beat on them whenever you may catch a small number of heads that either are a little too close to the outer range of tolerance for a spec(s) and send them back to them. That definitely puts the factory on notice that they do need to watchdog your stuff more. The squeaky wheel does gets greased all over the world in other words.

But in terms of weighting for MOI matching, that's something that is real hard to do if you do not design your heads with internal weight addition capability. since 97, every driver, wood, hybrid, iron, wedge I have designed is made with a weight bore down at the bottom of the shafting bore. The weight bore can accept little epoxied in weight plugs from 1g to 9g when necessary to achieve a specific swingweight or MOI for the built club. I have to do that in my designs because we sell only to custom clubmakers who will be custom assembling the heads with all ranges in shaft weight, to a variety of lengths, with a variety of grip weights, to a variety of swingweights and MOIs. And some of my head designs have a 2nd such weight chamber on the head when the head shape, size, design lends itself to being able to put a 2nd weight addition location in the head. You can't possibly be in the custom business without such weight change capability because of all the ranges in length, shaft weight, grip weight, swt/MOI that clubmakers will need to custom build custom fit clubs.

With the OEMS, they don't tend to do this because their heads are chiefly being used to build clubs to one series of standards for length, shaft weight, grip weight and swingweight. So they simply calculate what final head weight is needed for each club to have the factory manufacture the heads to that headweight with no internal, specific weight change feature. Yes, some OEMs will shoot sticky glue in their driver,wood,hybrid heads when they need to add weight, which is fine. Or use tip weights in the shafts, which is also fine. But again, they build only to one set swingweight for their stock clubs so as much as possible they try to weigh sort their heads upon arrival from the factory to avoid the extra time consuming step to shoot glue inside the head as much as possible.

Either that or many of them just have the head production factory do the stock assembly of their clubs to save money. That's become more and more of a process done outside their companies. so anything custom they get orders for would get built in house, but as many have found, when you ask most OEMs for custom lengths, shaft weight, they are very limited in what swingweight they can hit because of this.

[T.Beau]

[quote name='TomWishon' timestamp='1427744406' post='11247085']
[quote name='T.Beau' timestamp='1427738181' post='11246243']
i can see where MOI matching can be relevant if you are matching a set of irons. but what about the woods? wedges? wedges are often swung in diff manners and at diff speeds, and woods are woods...they are pretty much longer than the irons so i think that would bring other dynamics into play. also the sizes and shapes and balances are all different. so do you try and match everything up, or just match the irons, or match woods to woods?
in tennis swingweight is your version of moi matching. a racquet is mounted on a rdc machine and is swung on a horizontal axis which produces a numeric output. it's pretty revealing until you are trying to match say 6 frames for an advanced player and then it becomes pretty convoluted and not of much value even though the length of all the racquets are identical. you could have 6 racquets of identical swingweight which perform and feel quite differently (depending upon a players sensitivity to specs).

what really helps is if the racquets arrive w. tight tolerances to begin with..makes matching much easier and more successful. to that end, i bet your stuff comes to you w. tighter tolerances than the hugely mass produced stuff. i would think head specs being on target is most impt since the head is located at the end of the stick

i know that moi is also measured for hockey sticks.....and i bet for baseball bats, and who knows what else in the world of sports
[/quote]

I am aware that there has been a device for swingweight measurement on rackets for some time. I don;t watch it much, but I do see that one of the industry's leading clubmaking machinery makers, golfmechanix.com, does make a new form of such a machine for rackets. I also have spoken with guys who are in the hockey stick and bat business and am aware that they too pursue a form of MOI measurement and fitting their participants to a specific MOI. Haven't spoken to them to the point to ask about specifics on that though as I do not have that close of contact with those guys in my day to day doings.

I do recall way back in the early to mid 90s when driver heads compression molded from graphite had a few years of popularity, one factory I worked with that made our comp molded graphite heads was chiefly a racket maker because the process for manufacturing rackets was also compression molding. I visited this factory on one of my many trips over to Taiwan at the time and had the chance to see the complete process of racket production. This factory was a major supplier to Wilson for rackets at the time and in fact when I was there, they were finishing up a big number of rackets that they had made for Pete Sampras. I forget the model name of the racket but they were finished in a cobalt blue paint, in case you may remember which one it was from that era.

Anyway, my point in mentioning that is the fact that from what you say about racket variations in weight distribution, I can now relate to what you say. One of the big things that struck me in watching them mold the frames that seemed "odd" was how they just "crammed" the sheets of the composite pre preg into the molds. In other words, it did not seem to me at the time that things were all that precise in other words. Not precise in the sense of how precise graphite shaft makers are to very carefully cut identical sheets of pre preg for each shaft design for each wrap step in the procedure.

I certainly try to keep tolerances as tight as I can on the heads I design. Most of that in our business is determined by what factories you choose to work with, AND how much you prove to them that you are watching specs on each production run. The better head making factories most definitely have tighter tolerances built into their production procedures, machinery, worker training, etc. And for this, you pay more because it costs them more to do all those things. It also is good to beat on them whenever you may catch a small number of heads that either are a little too close to the outer range of tolerance for a spec(s) and send them back to them. That definitely puts the factory on notice that they do need to watchdog your stuff more. The squeaky wheel does gets greased all over the world in other words.

But in terms of weighting for MOI matching, that's something that is real hard to do if you do not design your heads with internal weight addition capability. since 97, every driver, wood, hybrid, iron, wedge I have designed is made with a weight bore down at the bottom of the shafting bore. The weight bore can accept little epoxied in weight plugs from 1g to 9g when necessary to achieve a specific swingweight or MOI for the built club. I have to do that in my designs because we sell only to custom clubmakers who will be custom assembling the heads with all ranges in shaft weight, to a variety of lengths, with a variety of grip weights, to a variety of swingweights and MOIs. And some of my head designs have a 2nd such weight chamber on the head when the head shape, size, design lends itself to being able to put a 2nd weight addition location in the head. You can't possibly be in the custom business without such weight change capability because of all the ranges in length, shaft weight, grip weight, swt/MOI that clubmakers will need to custom build custom fit clubs.

With the OEMS, they don't tend to do this because their heads are chiefly being used to build clubs to one series of standards for length, shaft weight, grip weight and swingweight. So they simply calculate what final head weight is needed for each club to have the factory manufacture the heads to that headweight with no internal, specific weight change feature. Yes, some OEMs will shoot sticky glue in their driver,wood,hybrid heads when they need to add weight, which is fine. Or use tip weights in the shafts, which is also fine. But again, they build only to one set swingweight for their stock clubs so as much as possible they try to weigh sort their heads upon arrival from the factory to avoid the extra time consuming step to shoot glue inside the head as much as possible.

Either that or many of them just have the head production factory do the stock assembly of their clubs to save money. That's become more and more of a process done outside their companies. so anything custom they get orders for would get built in house, but as many have found, when you ask most OEMs for custom lengths, shaft weight, they are very limited in what swingweight they can hit because of this.
[/quote]

thanks for all the info tom. interesting stuff. so this explains why you can get two of the same drivers that dont feel close to the same soundwise? a friend of mine had 2 ping rapture drivers...they both swung the same to me, but the ball feel was seriously different....i thought maybe they made a mid model spec change or something, but sounds like one driver was hot melted to bring it up to spec and the other was not. i liked the more muted feel of the sticky glued one, but sure wouldnt add that to a head that was already heavy enough. they were like playing two diff clubs. easy matter to add weight to a head, but hard to remove....for the tennis racquets the pros used....oem would make a lighter run for the pros..we would then shoot the handles w. varying amounts of silicone (which dampened the shock and added static weight) and lead up the heads under the bumper guard to get them to swing a certain way....the weight ended up being most concentrated at both ends of the racquet which did seem to make for the most effective use of the weight (have no idea why)..i mostly just playtested. (maybe a similar analogy would be a ping iron w. cushin insert as those have those weight ports in the head). never had much success w. counterweighting. sounds like your heads come in to you lighter too.

as to the Sampras racquet. pretty unusual, but he played the same racquet model from his junior days until he retired. wilson pro staff ps85. black in colour. while that model he used ended up being made in China, his personal racquets never were. originally they were made in chicago (they all were) and then the island of St Vincent (go figure). they always flew the black pro staff graphics like the chinese verson. those cobalt blue ones were prob some sort of pete sampras autograph model that were being sold at wal-mart for 29.95. likely a reason why they just stuffed the prepreg into the mold the chinese were just telling you stuff as they are prone to do anyway, likely more info than you wish to process...

related to golf, racquets like Sampras used were also known as 'blades' (thin beamed, low powered, heavier, harder to flush hit) , and the same types of 'discussions' happened in the tennis forums as here about the magic of the blade federer used the sampras model for much of his career (last of the mohicans). when he switched to something less demanding, all the blades controversy went away and the tennis forums seem to be a much more peaceful place

[TomWishon]

[quote name='T.Beau' timestamp='1427749796' post='11247623']

thanks for all the info tom. interesting stuff. so this explains why you can get two of the same drivers that dont feel close to the same soundwise? a friend of mine had 2 ping rapture drivers...they both swung the same to me, but the ball feel was seriously different....i thought maybe they made a mid model spec change or something, but sounds like one driver was hot melted to bring it up to spec and the other was not.
[/quote]

Couple of possible reasons for this. One is most definitely the +/- tolerance in the COR as happens because of variations in the face thickness primarily. It's most definitely possible within a run of just about any company's driver heads to see some come off the line with a COR up around 0.825 and some down around 0.810-815. Very good players with a refined sense of feel can note such differences due chiefly to the +/- tolerance in face thickness.

The other one can be the sticky glue injected into all heads that is chiefly done to catch any rattles that could come about after the head is put into play. That glue when injected is more viscous so until it begins to semi-cure and lose its viscosity to stay put in one place inside the head, it is possible for the the head to be put in a position that allows the glue to flow and set up on the back of the face. Which can affect the sound and impact feel for a sensitive player.

As to the actual COR of a driver, the very best way to know what you have in terms of final COR of your driver is to go hit shots on a good launch monitor like a TrackMan or FlightScope and watch for the smash factor for any shots you hit on center. Smash factor is directly related to COR so if you have a driver with a high COR close to the limit, the smash factor will be 1.48-1.49-1.50. If the COR is lower, so too will the smash factor for on center hits.

[Dan Drake]

The leader at the NCAA Championships this week plays his 3i-LW all at 37.5" so that he can stay in the same posture.

https://vimeo.com/121580539

I'm quite sure they are MOI matched as well.