Dear sammy,
The numbers I have seen for putter impact times range from about 0.005 seconds (1/2 ms) to 0.001 seconds (1 ms). This is what
Dr Norman Lindsay says:
"A recent paper in Science and Golf IV by Professor Ieuan Jones of Flinders University presents convincing evidence that when you hit a golf ball, the force and duration of the impact obey the Hertz theory very accurately. Jones studied ball impacts over speeds corresponding to a gentle Ôtap inÕ with a putter and up to a full drive down the fairway. Over this range of speeds the impact duration varied from 0.85 milliseconds for a gentle tap-in to 0.37 milliseconds for a drive. So the rule is, the faster the swing speed, the shorter the dwell time.
The Ôdwell timeÕ for a drive is just less than half that for a gentle putt, even though the ball speed off a driver is about 50 times faster than a tap-in. On the putting green, the variation in dwell time for different putt strengths is very much less. For example, on a level green, with the same putter and the same ball, a 10-foot putt will have just less than 15% more dwell time than a 40-foot putt.
The Jones study focussed on how accurately the Hertz theory predicts impact dynamics of one type of golf ball. The ball-hitting implement used in his experiments was made of stainless steel but was very much heavier than a putter head. Replacing this with an average weight putter head would reduce the values he obtained by about 6%. However, different weight putter heads do not change dwell time by much. The dwell time for a 450 grams putter head is only 3% greater than for a head weight of 250 grams.
The property of balls and putters that makes the most difference to dwell time is their hardness. Balata covered balls and elastomer face inserts give longer dwell time than harder materials such as Surlyn or steel, but even these soft materials do not increase dwell time significantly. The Hertz equations use basic elastic constants (YoungÕs modulus and PoissonÕs ratio) whereas golf balls and putter inserts are usually specified in ÔShore HardnessÕ scales measured by a hardness tester called a ÔdurometerÕ. This makes it difficult to apply the Hertz equations directly.
What we do know is that with any flat metal-faced putter, the dwell time is almost entirely determined by the ball material so there is no measurable difference between the dwell time from ÔsoftÕ metals like aluminium or copper and ÔhardÕ metals like stainless steel. This is because metal putter faces are much harder than golf balls and all the impact deformation occurs in the ball. The Hertz equations also tell us that replacing a metal putter face with an insert made of the same material as the golf ball cover increases the dwell time by only 32%.
Since The Rules of Golf prohibit inserts that are softer than a golf ball, it is very unlikely that ÔlegalÕ inserts could increase dwell time by more than 40% to 50% compared to the value obtained with a steel face and a balata covered golf ball. A way of getting round the rules would be to produce a very soft-covered golf ball - much softer than alata - but his would be almost unplayable. To prevent this anomaly, a specification that face inserts must be no less than 85 on a Shore A durometer scale is included in A Guide to the Rules on Clubs and Balls. "
Here are five graphics relating to "dwell time":
A Durometer to measure surface hardness:
The Zwick Durometer:
Lindsay: dwell times for different ball cover hardness (C-Groove putter with 10-foot putt on balata (0.8 ms) and on surlyn covered (0.6 ms) balls):
Lindsay: dwell time for different face insert hardness (Taylormade Nubbins" insert with a 10-foot putt on a balata ball (just under 1.0 ms) and a Fisher soft-insert with a 10-foot putt on a balata ball (just over 1.0 ms)):
Fisher putters: dwell time from soft insert (2.2 ms versus metal face at 1 ms):
Lindsay says these Fisher measurements are exaggerated.
Summing up, putts from 10-feet to 40-feet on typical greens using standard Titleist Pro V1 balls with no special inserts probably have dweel times that range from 0.85 ms to about 15% shorter dwell time for the longer putt (roughly 0.12 ms less, or 0.63 ms). However, using balata balls and also using soft face inserts can nearly DOUBLE the dwell time of a 40-foot putt up to above 1.0 ms. This is hardly insignificant.
This added dwell time makes several differences. First, it feels different in terms of vibrations, sound, putter deceleration and rebound on impact, and duration. Second, increased dwell times translate to increased "impulse" which is increased "work" during impact, and this means more energy is transferred during impact so the ball rolls farther, and this means a smoother, slower blow goes as far with one of these added-dwell-time impacts than otherwise. Third, increased time-of-contact between ball and putter means it is more likely that changes in face angle during contact will effect the line and / or launch angle of the ball, for good or bad, instead of the shorter dwell time confining the physics more tightly to the initial putter face orientation with less time to change things.
Personally, my preference over time with different combinations seems to settle on a metal-face putter and a standard ball cover perhaps fairly softer than a surlyn covered ball. The added dwell time seems to be to open the door to problems more than it solves problems. I don't really believe added dwell time affects distance consistency much, as the golfer can get used to whatever he is using, but it is useful to point out that soft inserts, by increasing dwell time and impulse, do not necessarily send the ball on a shorter total roll than metal-face putters for the same blow, as this is counter-intuitive.
Again, the ball-putter physics suggests that the least velocity of the putter head at impact that the golfer can use is probably a good thing.
Cheers!
Geoff Mangum
Putting Coach and Theorist
PuttingZone.com
Golf's most advanced and comprehensive putting instruction.