Byrne on Stiff Shafts and Squirt

[iacas]

I'm watching the Byrne's DVD #1 (i.e. the VHS on a DVD, basically) and he says a stiff shaft is good because a "whippy" shaft "diverts the cue ball too much when using English.

Just to be clear: he's wrong, right? Stiffer shafts "push through" the ball while the "whippier" shafts "get out of the way" more, right?

These videos are, what, 20 years old or more?

 

[StevenPWaldon]

Sounds wrong to me. The thicker the shaft and taper, the more the cue will squirt (and the less the shaft will deflect). That's a part of the 'magic' behind the Z shaft (11.75 mm)

 

[TheBook]

I think that this debate has been going on for at least 20 years. I think Byrnes even mentioned something about someone that defined the difference between squirt and deflection.

Some opinions are that a stiff shaft will help you develop more consistancy and control. A lot of beginners seem to like the so called wimpy shaft because they seem to think that they can put more stuff on the cueball and all that fancy stuff makes them look like a better player, especially if the opposite sex is looking.

 

[Colin Colenso]

Predator works on the theory that squirt is wholly derived from what I call 'Rotation Induced Deflection' (RID).

While RID is clearly significant, I postulated another mechanism called 'Surface Property Induced Deflection' (SPID) that takes into account the gripping at the tip-CB contact interface, and affects the distribution of forces tranfered from the cue to the CB.

The reason stiff shafts may not deflect as much as the RID hypothesis would expect, could be that the stiff shaft helps to hold the tip onto the ball to achieve better gearing.

Just an idea. More testing is needed I think for more conclusive evidence.

 

[mikepage]

I'm watching the Byrne's DVD #1 (i.e. the VHS on a DVD, basically) and he says a stiff shaft is good because a "whippy" shaft "diverts the cue ball too much when using English.

Just to be clear: he's wrong, right?

Right, wrong.

Stiffer shafts "push through" the ball while the "whippier" shafts "get out of the way" more, right? [...]

This is wrong too.

We're talking about the effect of shaft flexibility on squirt here, but the following argument holds as well for the effect of shaft flexibility on cueball action, i.e., spin. In both cases there is none, or at least none of practical significance. Many pro players, pool-hall prophets, and cuemakers will tell you otherwise, but they too are wrong.

Imagine two diving boards, one set to as stiff as it can go (the fulcrum moved forward) and the other set to as whippy as it can go (the fulcrum moved back). Real diving boards can lift off the fulcrums (fulcra?), but imagine these diving boards are glued to the fulcra.

The stiff board will be harder to displace, will vibrate to a lower amplitude for a given push, and will vibrate at a higher frequency than the whippy board.

Hit the end of each board with a rubber mallet. Both will start vibrating at their respective fundamental frequencies.

Now imagine this in ultra slow motion. For the short time the mallet is in contact with the board, the end of the board may displace only a quarter inch. The end of the board will then continue to displace after the mallet strike is done. Meanwhile the information that it's been hit by a mallet is traveling down the board. Sometime later the board near the fulcrum gets the message about the mallet strike. How long this takes depends on the speed of the transverse wave. I imagine it's a few tenths of a second for a diving board.

Imagine dropping a superball on the ends of the two diving boards. The height of its bounce is the equivalent of squirt. If a board "gives" more, a superball will not bounce as high. Will the superball bounce higher off the stiff board than the whippy board? No, it won't. The superball will not know which is the stiff board because that information comes too late. What, then, will determine the amount of "give" for the boards? It is the mass of the parts of the end of the board that are moving during the short time the superball is in contact. This diving board endmass plays the same role as a shaft's endmass.

If you drill out the first foot or two at the end of a diving board and make it light, the superball will not bounce much off of it.

The sideways squirt part of the stick-ball collision comes from exciting this sort of transverse wave in the stick. We can get a rough estimate of the speed of this information by noting a typical transverse vibrational frequency of a shaft is 40 Hz and a typical wavelength is perhaps one meter. This suggests a speed in the ballpark of 40 meters per second which is the same as 40 millimeters per millisecond. Maybe this is off by a factor of two or three or something, but the basic idea is that for sideways energy transfer, the ball only knows about the first few inches of the stick. It doesn’t know the flex point is 14 inches back. It doesn’t know there’s a stainless steel joint, and it doesn’t know the players rear hand is doing a slip stroke.

The forward energy transfer, on the other hand—the push that propels the cueball forward--*does* know about the back of the stick. That’s because it is the longitudinal compression wave that governs this energy transfer, and the longitudinal sound wave through the stick is much much faster than the transverse bending wave. Instead of moving at tens of mm per millesecond, it moves at thousands of mm per millisecond –i.e., a few stick lengths during the millisecond contact time.

Mike page
fargo

 

[jsp]

post

Very nice explanation Mike!

To give an electronics analogy, your description of squirt and shaft endmass is similar to the characteristic impedance of a transmission line... (Warning, you man not want to proceed reading unless you want to take a nap. )

If you have a very long wire shorting out the two terminals of a signal generator and you perform a voltage step across its two terminals, the signal generator won't see a short-circuit right away, but instead will deliver an amount of current inversely proportional to the characteristic impedance of the wire (if it's a coaxial cable, the characteric impedance will be about 50 or 75 ohms, depending on the type of cable). The voltage step would have to travel all the way down to the end of the wire, reach the other terminal of the signal generator, and reflect back and travel down the wire again in the opposite direction before the input of the signal generator gets information that the other end of the wire is shorted (and thus deliver massive amounts of current through the wire and smoke your generator, unless you have it current-limited of course ).

So, in the electronics analogy, the characteristic impedance of the wire is similar to the endmass of a cue. So I guess if the impact time between cue and CB is much longer than a millisecond or two, such that the wave has time to propogate down to the bridge hand and back, then flexibility of the shafts WOULD matter, and that Bryne would be correct in saying that stiffer shafts would squirt less.

 

[Andrew Manning]

Right, wrong.


This is wrong too.

We're talking about the effect of shaft flexibility on squirt here, but the following argument holds as well for the effect of shaft flexibility on cueball action, i.e., spin. In both cases there is none, or at least none of practical significance. Many pro players, pool-hall prophets, and cuemakers will tell you otherwise, but they too are wrong.

Imagine two diving boards, one set to as stiff as it can go (the fulcrum moved forward) and the other set to as whippy as it can go (the fulcrum moved back). Real diving boards can lift off the fulcrums (fulcra?), but imagine these diving boards are glued to the fulcra.

The stiff board will be harder to displace, will vibrate to a lower amplitude for a given push, and will vibrate at a higher frequency than the whippy board.

Hit the end of each board with a rubber mallet. Both will start vibrating at their respective fundamental frequencies.

Now imagine this in ultra slow motion. For the short time the mallet is in contact with the board, the end of the board may displace only a quarter inch. The end of the board will then continue to displace after the mallet strike is done. Meanwhile the information that it's been hit by a mallet is traveling down the board. Sometime later the board near the fulcrum gets the message about the mallet strike. How long this takes depends on the speed of the transverse wave. I imagine it's a few tenths of a second for a diving board.

Imagine dropping a superball on the ends of the two diving boards. The height of its bounce is the equivalent of squirt. If a board "gives" more, a superball will not bounce as high. Will the superball bounce higher off the stiff board than the whippy board? No, it won't. The superball will not know which is the stiff board because that information comes too late. What, then, will determine the amount of "give" for the boards? It is the mass of the parts of the end of the board that are moving during the short time the superball is in contact. This diving board endmass plays the same role as a shaft's endmass.

If you drill out the first foot or two at the end of a diving board and make it light, the superball will not bounce much off of it.

The sideways squirt part of the stick-ball collision comes from exciting this sort of transverse wave in the stick. We can get a rough estimate of the speed of this information by noting a typical transverse vibrational frequency of a shaft is 40 Hz and a typical wavelength is perhaps one meter. This suggests a speed in the ballpark of 40 meters per second which is the same as 40 millimeters per millisecond. Maybe this is off by a factor of two or three or something, but the basic idea is that for sideways energy transfer, the ball only knows about the first few inches of the stick. It doesn’t know the flex point is 14 inches back. It doesn’t know there’s a stainless steel joint, and it doesn’t know the players rear hand is doing a slip stroke.

The forward energy transfer, on the other hand—the push that propels the cueball forward--*does* know about the back of the stick. That’s because it is the longitudinal compression wave that governs this energy transfer, and the longitudinal sound wave through the stick is much much faster than the transverse bending wave. Instead of moving at tens of mm per millesecond, it moves at thousands of mm per millisecond –i.e., a few stick lengths during the millisecond contact time.

Mike page
fargo

Very well written. Put another way, what we think of as "whippy" or stiff involves how far the end of the cue displaces, not how quickly it displaces, which is to say the inertia of its displacement. The end mass of the stick is what truly affects its inertia with respect to flexing sideways away from the center of the ball, and the contact is too short for the flexibility of the stick to come into play.

However, a useful tidbit of information which would be relevant to the initial question in this thread would be the relationship between shaft flexibility (easy to measure by feel) and shaft end mass (difficult to measure). I would guess that in general shafts with higher end mass are stiffer and shafts with lower end mass are less stiff, since wood density, diameter, and taper seem to affect both stiffness and end mass.

So I'd conclude in general that stiffer shafts do deflect more than whippier ones, even though stiffness isn't directly the reason for this, and there are more factors to consider.

-Andrew

 

[iacas]

Imagine dropping a superball on the ends of the two diving boards. The height of its bounce is the equivalent of squirt. If a board "gives" more, a superball will not bounce as high. Will the superball bounce higher off the stiff board than the whippy board? No, it won't. The superball will not know which is the stiff board because that information comes too late. What, then, will determine the amount of "give" for the boards? It is the mass of the parts of the end of the board that are moving during the short time the superball is in contact. This diving board endmass plays the same role as a shaft's endmass.

From a physics standpoint, the two are not analogous systems: you don't hit the cue ball with the side of your stick, nor is the diving board in motion. They're very different.

I appreciate the attempt, but if you're going to single out a bunch of people as being "wrong," I'd caution you to use better physics...

 

[mikepage]

From a physics standpoint, the two are not analogous systems: you don't hit the cue ball with the side of your stick, nor is the diving board in motion. They're very different.

I appreciate the attempt, but if you're going to single out a bunch of people as being "wrong," I'd caution you to use better physics...

Your description of the stiff stick plowing through the cueball not giving way and the whippy stick giving way to the cueball is inconsistent with the time scales of the interactions. But I think it's a common view, so I tried to explain the problem with the mental model with an analogy.

The diving board is not an analogy for the entire stick-ball interaction. There is, as you say, none of the main stick-ball interaction, the part that propels the ball forward. [I have other analogies for that ;-)] But the part of the interaction that causes squirt and the role of the flexibility of the stick *is* analogous to the diving board interactions I described.

mike page
fargo

 

[bruin70]

I'm watching the Byrne's DVD #1 (i.e. the VHS on a DVD, basically) and he says a stiff shaft is good because a "whippy" shaft "diverts the cue ball too much when using English.

Just to be clear: he's wrong, right? Stiffer shafts "push through" the ball while the "whippier" shafts "get out of the way" more, right?

These videos are, what, 20 years old or more?

it has always been my perception. in the case of 3 cushion and their use of billiard tapers, a player(byrne might know him) friend of mine expects deflection but CONSISTANCY with a billiard taper.

 

[mikepage]

Very well written. Put another way, what we think of as "whippy" or stiff involves how far the end of the cue displaces, not how quickly it displaces, which is to say the inertia of its displacement. The end mass of the stick is what truly affects its inertia with respect to flexing sideways away from the center of the ball, and the contact is too short for the flexibility of the stick to come into play.

However, a useful tidbit of information which would be relevant to the initial question in this thread would be the relationship between shaft flexibility (easy to measure by feel) and shaft end mass (difficult to measure). I would guess that in general shafts with higher end mass are stiffer and shafts with lower end mass are less stiff, since wood density, diameter, and taper seem to affect both stiffness and end mass.

I don't think there is such a clear relationship. The stiffness depends most on the taper between, say, 6 and 24 inches, while the endmass depends on the mass in just the first couple inches.


mike page
fargo

 

[Gabber]

finally.

Mike said,
"It doesn’t know there’s a stainless steel joint, and it doesn’t know the players rear hand is doing a slip stroke.

Thanks for a good well presented post Mike.


Gabber

 

[Cornerman]

I'm watching the Byrne's DVD #1 (i.e. the VHS on a DVD, basically) and he says a stiff shaft is good because a "whippy" shaft "diverts the cue ball too much when using English.

Just to be clear: he's wrong, right? Stiffer shafts "push through" the ball while the "whippier" shafts "get out of the way" more, right?

These videos are, what, 20 years old or more?

He's wrong not because of what you said, but because 20 years ago, squirt (cueball path deflection) wasn't as understood today.

As of today's understanding, stiffness has little to no effect on the cueball path.

Fred

 

[Jal]

...As of today's understanding, stiffness has little to no effect on the cueball path.

I think Steven Waldon has it right. It seems likely that shaft/ferrule flexibility is the principle determiner of a cue's squirt characteristic. The end mass approach is misleading, in my opinion.

One way to resolve this is to reduce the diameter of a cue and see how the squirt changes. Since a shaft's stiffness is proportional to its cross-sectional radius taken to the fourth power, reducing a 13mm one to 12mm should produce about a 27% decrease in its spring constant, and about as much reduction in the tangent of the squirt angle. Reducing it to 11mm should produce almost a 50% decrease.

There are some unknowns here, like just how fast the relevant stresses travel down the shaft. The above numbers assume that the effective cantilever length is at least around 3" by the time tip compression nears a maximum, and that the ferrule is not greatly stiffer than the shaft. Since a cantilever's spring constant is inversely proportional to the cube of it's length, this is important in that it makes the shaft and not the tip the dominant contributor to the stiffness of the system. Given that Predator gets its results by altering the shaft, the above assumptions are very likely correct.

Jim

 

[mikepage]

[...]
One way to resolve this is to reduce the diameter of a cue and see how the squirt changes. Since a shaft's stiffness is proportional to its cross-sectional radius taken to the fourth power, reducing a 13mm one to 12mm should produce about a 27% decrease in its spring constant, and about as much reduction in the tangent of the squirt angle. Reducing it to 11mm should produce almost a 50% decrease.

There are some unknowns here, like just how fast the relevant stresses travel down the shaft. The above numbers assume that the effective cantilever length is at least around 3" by the time tip compression nears a maximum, and that the ferrule is not greatly stiffer than the shaft. Since a cantilever's spring constant is inversely proportional to the cube of it's length, this is important in that it makes the shaft and not the tip the dominant contributor to the stiffness of the system. Given that Predator gets its results by altering the shaft, the above assumptions are very likely correct.

Jim

Would you elaborat on the "at least 3 inches" Jim? I'm not sure what calculation you're doing.

In the meantime, here is some experimental information a good model needs to explain or at least be consistent with.

Theshaft at www.fargopool.com/p314.jpg is very low squirt.

The never-before-seen whippy-miz-cue-from-hell is the second shaft. As you can imagine it is very whippy in one direction. It is far from radially consistent. And yet it is very high squirt in any direction. In fact I can't find any difference at all for the cueball by changing its orientation.

 

[cuetechasaurus]

So basicically what you guys are saying is this: If you measure the scategoriphical triumphants of the endoplasmic reticulum, you may come up with an ATP energy mitochondrion converter in which the pulsar rapidly propels, causing deflection in the stage II mitosis. Thanks, I see everything so clearly now.

 

[jsp]

So basicically what you guys are saying is this: If you measure the scategoriphical triumphants of the endoplasmic reticulum, you may come up with an ATP energy mitochondrion converter in which the pulsar rapidly propels, causing deflection in the stage II mitosis. Thanks, I see everything so clearly now.

No No No No. You got it ALL wrong. Not mitosis, but meiosis. Geez!

 

[jsp]

Would you elaborat on the "at least 3 inches" Jim? I'm not sure what calculation you're doing.

In the meantime, here is some experimental information a good model needs to explain or at least be consistent with.

Theshaft at www.fargopool.com/p314.jpg is very low squirt.

The never-before-seen whippy-miz-cue-from-hell is the second shaft. As you can imagine it is very whippy in one direction. It is far from radially consistent. And yet it is very high squirt in any direction. In fact I can't find any difference at all for the cueball by changing its orientation.

Hi Mike. Interesting experiment. Question though. Where exactly do you bridge the second shaft? From the location of the notch, it would seem as if the bridge hand would be placed between the notch and tip. Wouldn't a firm bridge anchor the shaft at the bridge location, such that the effect of the notch become less effective? Shouldn't the notch be between the bridge hand and the tip to get more accurate experimental results?

 

[mikepage]

Hi Mike. Interesting experiment. Question though. Where exactly do you bridge the second shaft? From the location of the notch, it would seem as if the bridge hand would be placed between the notch and tip. Wouldn't a firm bridge anchor the shaft at the bridge location, such that the effect of the notch become less effective? Shouldn't the notch be between the bridge hand and the tip to get more accurate experimental results?

Well I tried both. But mostly I bridged behind the notch as you say, so my bridge hand is not an issue.

mike page
fargo

 

[mikepage]

So basicically what you guys are saying is this: If you measure the scategoriphical triumphants of the endoplasmic reticulum, you may come up with an ATP energy mitochondrion converter in which the pulsar rapidly propels, causing deflection in the stage II mitosis. Thanks, I see everything so clearly now.

All right, all right.

The proof of the pudding is in the eating.

This sucker below makes a Meucci seem as stiff as a billiard cue on viagra.

And yet it squirts like a Banshee....

mike page<-- assumes everybody knows Banshees squirt a lot
fargo