Prestressed Shaft and Impact Deceleration

[jmessner]

Actually, bowing up of the shaft was a reference to a vertical frame of reference- that is the Sweetspot is out on the clubhead somewhere- not at the end of the shaft- so the shaft has to bend up or I think Maltby or someone referred to it as clubhead droop. If you have that going on and are looking at it from an angle as in those photo's above-then that alone would look as if the clubhead was ahead of the grip- or bowing forward when really it was just bowing up.

Of course, you bring up a good point- that if the center of gravity of the clubhead is behind the shaft- due to the construction of the club - then that would create a situation for the Swinger who is using centrifugal force- where by during the swing/release -the shaft would be bowing forward.

In that regard, again the Hitter and Swinger are going to have different shaft motions- due to their acceleration methods- and that's why you have the Pre-stressed shaft for the Hitter and the Wallop of Centrifugal force.

For the swinger using centrifugal force (bowing up- to the degree the sweetspot is out away from the end of the shaft i.e. the longer your clubhead the more the shaft will have to bow up or the more the clubhead must droop down)for the Swinger. Likewise, the wider the clubhead/face the more the center of gravity is moved back in relation to the shaft and the more the shaft would have to bend foreward to line the center of gravity up with the #3 pressure point.

Here is the important distinction to make- for the swinger using a driver where the center of gravity of the clubhead is behind the shaft alignment based on the construction of the club. During release centrifugal force will want to line the #3 pressure point or grip end of the clubshaft with the center of gravity of the clubhead i.e. the longitudindal center of gravity of the club itself- thereby creating a situation where the shaft would bow forward. But that wouldn't mean that you don't have a lagging clubhead- if you're pulling/pulling/pulling and creating centrifugal force, you would have clubhead lag- in fact based on the construction of the club- if the shaft was straight and not bowed forward- that would be a situation where you did not have lag if you were Swinging the club!

P.S. pulling/pulling/pulling is more a mechanical description and not a procedural description- because I just invision someone trying to pull/pull/pull to make their movement- so don't go out and do that.

Mike O - Ok, yes I think we're talking about the same thing - and you're right, clubmakers call it droop. I know nobody here gets Golf Digest, but the latest has a good picture of Camilo Villegas on the cover at impact from up the line that shows this. Put a straightedge on the handle and see how much the tip of the shaft has bent downward.

Also, your point on camera angle is well taken. However, I would say that if you could get an image with the head say 6 inches or so before impact the droop would be pretty much invisible (because it's directly perpendicular to the camera angle) to a camera viewing face-on and you'd be seeing the forward or backward bending predominantly. That's why the deflection curves generated by strain gauges that indicate the kind of shaft behavior I described are somewhat more convincing to me. Still, the images I have seen with that just by chance have clubhead very near the impact point have not shown a lagging clubhead - but you never know.

Anyways, I think I've kind of beat this subject to death, but while I'm somewhat clear on the difference your referring to with swinging and hitting (longitudinal vs radial), I don't think I understand why the centrifugal (centripetal) force of the clubhead on the shaft would be much different between the two. I'm probably missing the point here but from my college physics days, the centrifugal force would be equal to the clubhead mass times the clubhead speed squared all divided by the radius of the circular motion of the clubhead (at high clubhead speeds it turns out to be quite a large force). None of these factors would seem to be dependent on swinging or hitting given the same clubhead speed(maybe radius slightly?). Maybe TGM is using the term centrifugal force differently than the literal scientific meaning. I'll have to go look at the book again.

BTW, I'm not sure I've been very clear on this, but I wasn't suggesting that there was never clubhead lag in the swing - there certainly is and it is lagging for most of the downswing until the point the clubhead reaches a speed where the centrifugal force overwhelmes any pushing or pulling acceleration on the shaft and drives toward the center of gravity alignment we discussed. Maybe you're saying the same thing in your last paragraph before the PS? Good discussion.