At 02:29 PM 8/15/2007, Richard Kempton wrote:
DaveT (& Tflan)
Just wanted to query something you both said below.
Unless Tom Wishon has misquoted SAM Puttlab's research (or I've
misinterpreted what TW wrote) in his 'Commonsesnse Clubfitting' book, it
seems that is is, in fact, possible to 'launch' a ball off a putter face at
an upward angle relative to the green, with topspin and without the hands
significantly trailing the clubhead.
On p. 389-390 he says:
"[Sam PuttLab's research] ... has determined that the ideal roll performance
for a putt is achieved when the putt is struck with a putter head of 1º loft
RELATIVE TO THE GROUND with a stroke that generates a 3º to 4º upward angle
of attack .."
(BTW, the CAPS above are mine, not TW's)
If my understanding of that is correct, it means that if the putter loft at
impact RELATIVE TO THE GROUND is plus 1º, then RELATIVE TO THE UPWARD PATH
OF THE PUTTER HEAD it is between minus 2º & minus 3º (thus applying
topspin). Unfortunately, maths was never my strong point, so I may have that
wrong, although it seems logical. Anyone?
Three diagrams follow on p. 390, the last of which shows the ball taking off
on a slightly upward path, BUT WITH TOPSPIN (the putter face impacts the
ball just BELOW the equator, but the force vector appears to pass through a
point directly ABOVE the ball CG). The caption reads as follows:
"When the net loft of the putter is less than the angle of attack, the force
is applied above the CG of the ball and topspin is generated for a better,
more consistent roll of the ball on the green."
Comments?
Sure!
That's a good observation, and it makes
reasonable sense according to physics. But it's
not Wishon's bottom line, when you read the whole chapter.
He agonizes a bit about whether a clubfitter
should "fix" the golfer's swing before fitting
clubs. He decides against it for himself, but
remains agnostic on the question in general.
So, if you take his route, you are fitting to the
angle of attack that the golfer putts with NOW.
And even if you do give them a putting lesson....
A 3-4 degree positive angle of attack is pretty
extreme -- and it's what the SAM stuff says is
optimum. So you are probably working with between
1* and some negative angle of attack.
Moreover, the hands may be ahead of the clubhead
in the putt -- or, for that matter, behind it.
That may be adding or subtracting effective loft at impact.
The bottom line (on p391) is, "In general, what
you are shooting for is an EFFECTIVE LOFT of 4
degrees at the moment of impact. In the absence
of [SAM equipment] that seems to be a good
compromise." In the context of the rest of the
paragraph, his EFFECTIVE LOFT (Wishon uses
italics, I used caps because email doesn't do
italics) seems to be the algebraic sum of:
*** the loft of the putter.
*** the angle of attack.
*** the delofting/lofting effect of the golfer's stroke.
In very few cases does that work out to a negative loft for the putter.
_______________________
Getting back to the convex-face putter (Spherical Blade or Teardrop)...
Even if this analysis says you SHOULD have a
negative loft, you should have the right negative
loft for you. NOT some random loft depending on
how high above the ground the putter was this
particular stroke. How much random loft variation could we expect?
The Werner-Greig study I cited in my previous
post says that the putter height variation is
about 0.3 inch for a scratch golfer and almost
0.5" for a bogey golfer. If we assume a 5" roll
radius (that's about what it looks like in the
picture), then a scratch golfer would have a 3.4*
loft variation and a bogey golfer more than 5*.
That does not sound like the right way to build a putter.
Hope this addresses what you were asking.
DaveT
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