@DrDave, Bob Jewett - valid deflection test?

Meucciplayer said:
dr_dave said:
A test like that can be valid if the shooter aims consistently, hits the CB in the same place with every shot (and with the same cue elevation), uses a consistent CB speed, and does a large number of trials. It is difficult to verify these things from the video.

An easier and more reliable way to test and compare shafts is to measure the natural pivot length using the simple procedure starting at the 4:22 point in the following video:

NV J.12 - How to Select a Pool Cue, Cue Ball Deflection, Carbon Fiber, Revo vs. Cuetec

Regards,
Dave

PS: FYI, guidelines that should be followed when doing shaft CB deflection tests are summarized here:

Rules of CB Deflection Testing
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Thank you very much, DrDave. Yes, I know your deflection tests and have used them myself already. For me personally, it was more of an exercise to find out my personal pivot point, as others have stated. A little curiosity might also have been involved WRT the deflection properties of my Meucci shafts.

I used another test you recommended before your last videos. Back then, your set-up consisted of a ball lying about 1 diamond from a corner pocket in a 45 degree angle. You had to ensure you could accomplish a perfect stop shot and then do the same stop shot with varying pivot lengths and English to find out the natural pivot length. I suppose you now prefer the new method with the cueball passing between the 2 balls in the jaws of a pocket? (Well, the old method worked for me to find out my natural pivot length). I suppose your new method has a little less margin for error.
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The new test (shooting into a pocket with "sentinel" balls, with less distance and more speed, with the cue as level as possible) is much more reliable. The older stop shot approach requires aim adjustment for object ball throw, so it doesn't yield the true natural pivot length.

Meucciplayer said:
So, I guess it is safe to say that your current method of determining deflection/natural pivot length is way superior to the method shown in the [older] video.
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Yes.

Regards,
Dave
 
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Thank you again, DrDave. Your website has always been a treasure trove and I would not know a lot of (scientific) approaches to pool without you. I only wish I could remember all the wisdom included there and then apply it. But I am working on it.
 
Bob Jewett said:
I see a technical issue with the test that might be a problem.

It looks like the distance of the shaft from the cushion is set by the thickness of his finger if his finger is tight against the nose of the cushion. It is good to control the left-right position of the cue stick. The problem though is that you want to control the other side of the shaft -- the one that hits the ball. (More exactly, it would be a point a little inside the other side of the shaft where the actual contact point on the ball is.)

Imagine a 2-inch diameter shaft. The bridge will force him to hit almost on the wrong side of the cue ball. That is an extreme case just to show you the direction of the influence. This points out that if the shafts are different diameters and the bridge does anchor the side of the shaft to the rail a systematic error is introduced.

When I demo squirt I show the shot I originally proposed to measure squirt: play a 90-degree cut shot with a ball frozen on the center of the far end rail by hitting rail first and using extreme inside english. I ask the student to estimate where my stick is actually pointed on a shot that makes the ball, such as for what looks like a full-ball aim or even aim on the wrong side of the ball. (I try to be near the miscue limit.)

Of course I should hit the ball at the same speed and with the same spin for each cue stick I do the demo with and maybe I come close to such control. For the purpose of demoing squirt and the fact that different cues have different amounts of squirt, that's not so important. In fact, I may have a similar error as the OP test for shafts of different diameter if I'm setting up the middle of the shaft in the same place -- I will have less side spin for thick shafts.
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My unscientific deflection test just to compare whether one shaft deflects more/less than another shaft:

Take a brightly colored easy to see the edges object ball like the 3-ball or 5-ball and freeze it to the center end rail where you rack the balls. Set the cue ball directly on the headspot on the opposite end of the table. Keeping the cue as level as possible throughout the stroke to eliminate any possible swerve, apply maximum L or R spin, attempting to pocket the object ball in the corner pocket (right corner if using right spin to the left edge of the object ball or left corner using left spin to contact the left edge of the object ball) by contacting the ball and rail at virtually the same time, with a medium paced stroke. You'll need to do this about 10 to 15 times until you are locking in on exactly how much deflection to compensate for in your aiming in order for the cue ball to contact the rail/ball at the correct angle to pocket the ball in the corner.

Then switch to the other shaft and do the exact same thing, making sure to use the exact same amount of spin and shooting the shot at the exact same pace. Do it for 10-15 attempts, but you should almost immediately be able to tell the difference between the two shafts as to whether you're needing to compensate more or less in order to lock in on where you need to aim to pocket the object ball.

I recently did this test with my Mezz EXPro shaft and my Mezz WX900 shaft, and realized virtually immediately on the first few attempts that the WX900 shaft deflects far less than the EXPro shaft. I'm certainly not saying this is an easy shot or one that you would ever attempt during a match, but once you lock on your shaft and the amount of deflection you need to compensate for in your aim, you might be amazed at how often you can successfully pocket this shot, or come very close to pocketing it.
 
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Bob Jewett said:
When I demo squirt I show the shot I originally proposed to measure squirt: play a 90-degree cut shot with a ball frozen on the center of the far end rail by hitting rail first and using extreme inside english. I ask the student to estimate where my stick is actually pointed on a shot that makes the ball, such as for what looks like a full-ball aim or even aim on the wrong side of the ball. (I try to be near the miscue limit.)

Of course I should hit the ball at the same speed and with the same spin for each cue stick I do the demo with and maybe I come close to such control. For the purpose of demoing squirt and the fact that different cues have different amounts of squirt, that's not so important. In fact, I may have a similar error as the OP test for shafts of different diameter if I'm setting up the middle of the shaft in the same place -- I will have less side spin for thick shafts.
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I like that test because it translates well into the “how much deflection is there” question. You can see if the ball went off-line an inch, or a full ball, etc.

Dr. Dave’s pivot-point test is good too, especially if you use an intenti9nal pivot aiming system, but doesn’t translate well to that real-world “how much deflection is there” if you don’t think in terms of pivot. And I’ve tried it on low-deflection shafts and find that I end up with an unnaturally long bridge length.

How about this for another possible test: Set up the impossible cut shot, say, from half table away, and then use a back-hand pivot for the english. Then see where you’re aiming prior to the pivot: At the ghost ball, half the object ball, 3/4, etc. As long as you’re consistent with the bridge length and pivot etc., you should be able to compare cues.
 
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