Squirt. End Mass and Cue Flexibility.

[dr_dave]

I have a DymondWood playing cue which is VERY STIFF and it has some of the lowest cue ball squirt/deflection characteristics of any cue.

What a player describes as "stiff" doesn't always directly correlate to the transverse stiffness that affects squirt (CB deflection).

The "feel," "hit," "feedback," "playability," and "stiffness" perceived by a player are very qualitative things that aren't always easy to characterize with measurable physics effects. Also, sometimes one player will assess these things totally differently from how another player assesses them (even for the exact same cue).

Regards,
Dave

 

[dr_dave]

Now I'll get to work on my new diagram and eventually post it with a detailed explanation.

Stay tuned,
Dave

PS: I might not have time for this until Tuesday, but I'll do my best.

 

[JoeyA]

Thanks. Now I just have to understand what transverse stiffness is. Or not. Lol


JoeyA

What a player describes as "stiff" doesn't always directly correlate to the transverse stiffness that affects squirt (CB deflection).

The "feel," "hit," "feedback," "playability," and "stiffness" perceived by a player are very qualitative things that aren't always easy to characterize with measurable physics effects. Also, sometimes one player will assess these things totally differently from how another player assesses them (even for the exact same cue).

Regards,
Dave

 

[dr_dave]

Thanks. Now I just have to understand what transverse stiffness is.

In relation to shaft "endmass" and squirt, it is the opposite of how "whippy" the 5-8 inches of the shaft closest to the tip is.

Regards,
Dave

 

[john coloccia]

If the shaft and butt had no mass, then not only would there be no squirt, the CB would not even move when struck with the cue (with either a center-ball or off-center hit)!!!

...
...

Bizarre theoretical examples like this often seem wrong because they are not practically possible, so they sometimes go against our intuitive understanding.

Regards,
Dave

I'm sorry, but I don't agree with this. It is only true if you're considering only the inertial motion of the cue and the ball. Ultimately, I'm holding the cue and for all practical purposes my weight may as well be infinite (i.e. I'm not moving). I guess you can calculate some momentum transfer through me to the Earth, and maybe include the Sun and planets too if you want to be really precise, but I have a feeling that simply considering the bulk of my body as rigid is probably good enough.

But that said, I'm kind of satisfied with Cornerman's explanation that there's enough compliance everywhere else in the real system that by the time it has a chance to be significant (i.e. by the time my body squishes enough to have any effect on the cue), the ball is long gone and it's completely irrelevant. That makes sense to me and seems very plausible.

edit:
Dave, just to be clear I like your site and I'm appreciative of all the work you've put into it! I just don't agree that imagining a stiff cue with no mass should be invalid, and really it should just boil down to a simple free body diagram for the cueball, at least as a good approximation. But like I said, I'm satisfied that the stiffness doesn't matter (lateral stiffness) because you guys have looked at it and determined that real people just don't/can't hold their cue rigidly enough to matter.

 

[dr_dave]

If the shaft and butt had no mass, then not only would there be no squirt, the CB would not even move when struck with the cue (with either a center-ball or off-center hit)!!! To impart sideways momentum (squirt) to the CB, this momentum must be balanced by equal and opposite sideways momentum in the shaft and cue (for momentum to be conserved), and momentum (mass x velocity) requires mass.

Now, if the shaft were very stiff and had little or no mass, but the butt did have mass (so the CB could actually move forward), the transverse wave would travel through the shaft very fast and involve mass of the butt in the "effective endmass." In this case, there would be squirt.

Bizarre theoretical examples like this often seem wrong because they are not practically possible, so they sometimes go against our intuitive understanding.

I'm sorry, but I don't agree with this. It is only true if you're considering only the inertial motion of the cue and the ball. Ultimately, I'm holding the cue and for all practical purposes my weight may as well be infinite (i.e. I'm not moving). I guess you can calculate some momentum transfer through me to the Earth, and maybe include the Sun and planets too if you want to be really precise, but I have a feeling that simply considering the bulk of my body as rigid is probably good enough.

But that said, I'm kind of satisfied with Cornerman's explanation that there's enough compliance everywhere else in the real system that by the time it has a chance to be significant (i.e. by the time my body squishes enough to have any effect on the cue), the ball is long gone and it's completely irrelevant. That makes sense to me and seems very plausible.

edit:
Dave, just to be clear I like your site and I'm appreciative of all the work you've put into it! I just don't agree that imagining a stiff cue with no mass should be invalid, and really it should just boil down to a simple free body diagram for the cueball, at least as a good approximation. But like I said, I'm satisfied that the stiffness doesn't matter (lateral stiffness) because you guys have looked at it and determined that real people just don't/can't hold their cue rigidly enough to matter.

John,

Thank you for pointing this out. I agree. If you consider the grip pushing the cue forward (which is usually not considered since the grip has no appreciable effect during tip contact with a real cue and a real person), then the CB would move forward, and the grip hand could contribute a small amount of "effective endmass" (if the fictitious cue were in fact extremely stiff, and if the grip were extremely tight and bony), which could cause a small amount of squirt (CB deflection).

For those interested, an explanation of why the grip hand has no practical affect during tip contact with typical equipment and human players, see: effects of light vs. tight grip.

Regards,
Dave

 

[JoeyA]

So exactly how do you measure transverse stiffness?

JoeyA

In relation to shaft "endmass" and squirt, it is the opposite of how "whippy" the 5-8 inches of the shaft closest to the tip is.

Regards,
Dave

 

[LAMas]

So exactly how do you measure transverse stiffness?

JoeyA

The mass of a CB is around 6 ounces what is your bridge length behind the CB and how much does your cue bend?
A 13mm diameter shaft = ~.44" square.

http://www.botlanta.org/converters/dale-calc/bending.html

???

 

[dr_dave]

So exactly how do you measure transverse stiffness?

Joey,

The blue stuff below is all you really need to know, but I've also included justification for those interested.

To measure the "transverse stiffness" important in discussions concerning squirt (CB deflection) and endmass, rigidly support the entire cue on a table (with clamps and/or heavy weights) so only the portion "active" during tip contact is hanging over the edge of the table. "Endmass" involves only the 5-8 inches of the shaft closest to the tip, but the transverse wave travels farther down the shaft during tip contact (10-16 inches) since the transverse wave must travel to and back from mass for it to be "felt" by the tip during contact, so I suggest 8 inches (as a good average value of flex length during tip contact). Then hang a weight from the tip and measure how much the tip moves down (i.e., how much the shaft end flexes). The transverse stiffness is:

k_trans = (weight applied to tip) / (distance tip moves down)

See TP B.19 for an example calculation (using the measurement I took with a Predator Z2 shaft).

The shaft transverse stiffness is inversely proportional to the amount the shaft flexes. With a smaller stiffness, the shaft flexes more; and with a larger stiffness, the shaft flexes less. It is important to not confuse the "deflection" of the shaft (how much the tip moves down when the weight is applied) with the CB "deflection" caused by the shaft. A shaft that "deflects" more will usually produce less CB "deflection" (squirt), unless the tip and/or ferrule and/or shaft end are heavy.

Regards,
Dave

PS: The "stiffness" or "whippiness" a player "feels" applies more to the entire cue. I think that could be quantified similarly by extending more of the cue over the edge of the table or by measuring frequencies (rates) of vibration of the cue during a hit (e.g., with an accelerometer).

 

[Drop The Rock]

If you have hit with a Mezz shaft you'll know LD is achievable with a stiff shaft.

 

[LAMas]

If you have hit with a Mezz shaft you'll know LD is achievable with a stiff shaft.

Mezz EX Pro Shaft

The EX Pro shaft features the next generation Hybrid carbon core (HCC) and the EX front-end technology. The HCC strikes the right balance between hardness and flexibility creating more power without any loss of cue ball control. Reduced cue ball deflection along with additional power increase is provided by the enhanced EX front-end technology. These technological advancements together with the EX Pro Taper and the Zan Plus Soft Tip makes the Mezz EX Pro the best low deflection shaft in the world.
Retail $400.00

 

[JoeyA]

Great. Thanks.
JoeyA

Joey,

The blue stuff below is all you really need to know, but I've also included justification for those interested.

To measure the "transverse stiffness" important in discussions concerning squirt (CB deflection) and endmass, rigidly support the entire cue on a table (with clamps and/or heavy weights) so only the portion "active" during tip contact is hanging over the edge of the table. "Endmass" involves only the 5-8 inches of the shaft closest to the tip, but the transverse wave travels farther down the shaft during tip contact (10-16 inches) since the transverse wave must travel to and back from mass for it to be "felt" by the tip during contact, so I suggest 8 inches (as a good average value of flex length during tip contact). Then hang a weight from the tip and measure how much the tip moves down (i.e., how much the shaft end flexes). The transverse stiffness is:

k_trans = (weight applied to tip) / (distance tip moves down)

See TP B.19 for an example calculation (using the measurement I took with a Predator Z2 shaft).

The shaft transverse stiffness is inversely proportional to the amount the shaft flexes. With a smaller stiffness, the shaft flexes more; and with a larger stiffness, the shaft flexes less. It is important to not confuse the "deflection" of the shaft (how much the tip moves down when the weight is applied) with the CB "deflection" caused by the shaft. A shaft that "deflects" more will usually produce less CB "deflection" (squirt), unless the tip and/or ferrule and/or shaft end are heavy.

Regards,
Dave

PS: The "stiffness" or "whippiness" a player "feels" applies more to the entire cue. I think that could be quantified similarly by extending more of the cue over the edge of the table or by measuring frequencies (rates) of vibration of the cue during a hit (e.g., with an accelerator).

 

[JoeyA]

Hmmm. With statements like that, you make me want to try one.
JoeyA

Mezz EX Pro Shaft

The EX Pro shaft features the next generation Hybrid carbon core (HCC) and the EX front-end technology. The HCC strikes the right balance between hardness and flexibility creating more power without any loss of cue ball control. Reduced cue ball deflection along with additional power increase is provided by the enhanced EX front-end technology. These technological advancements together with the EX Pro Taper and the Zan Plus Soft Tip makes the Mezz EX Pro the best low deflection shaft in the world.
Retail $400.00

 

[JoeyA]

Hmmm. With statements like that, you make me want to try one.
JoeyA

Hahaha. I see it is their words, not yours.
JoeyA

 

[greyghost]

Hmmm. With statements like that, you make me want to try one.
JoeyA

i told you that mystery cue of yours plays very similar to the way I been making my personal cues since 2010.....the only thing that add says that i don't remember that cue having a ton of is touch. Not that it was a complete rail by any means at all....but if you want to add that touch while still having the straightness of aim and cut abilities and power......then just use an actual tone wood like rosewood or african blackwood and build it 4pt style, maple for the rest as always.

try it on a hunch we'll call it...let me know what you think if you do

 

[Petros Andrikop]

This has been one of the most interesting threads of its kind to follow, congrats and thanks to everyone contributing, would it be possible that someone summarizes the most serious "conclusions" of this discussion in a post, everything worthy of mentioning, even if some contradict some other?
Thanks,
Petros

 

[LAMas]

Hahaha. I see it is their words, not yours.
JoeyA

Sorry,

I didn't provide a link to Mezz for I wasn't marketing but following up on what makes it different, in their words (not mine) than other LD shafts.

Everybody that is interested can Google Mezz shafts.

Has the Dr. tested it for squirt?

Be well.

 

[JoeyA]

Thanks, but I won't be changing anything or trying anything new.

JoeyA

i told you that mystery cue of yours plays very similar to the way I been making my personal cues since 2010.....the only thing that add says that i don't remember that cue having a ton of is touch. Not that it was a complete rail by any means at all....but if you want to add that touch while still having the straightness of aim and cut abilities and power......then just use an actual tone wood like rosewood or african blackwood and build it 4pt style, maple for the rest as always.

try it on a hunch we'll call it...let me know what you think if you do

 

[JoeyA]

Sorry,

I didn't provide a link to Mezz for I wasn't marketing but following up on what makes it different, in their words (not mine) than other LD shafts.

Everybody that is interested can Google Mezz shafts.

Has the Dr. tested it for squirt?

Be well.

This shaft is just becoming available in February 2016, so I doubt that Dave has tested it.

What Dave should do is provide scientific testing for all of the cue manufacturers. There might be a few that would take him up on his offer.


JoeyA

 

[The Renfro]

If you would like to talk privately, I'm good with that, but NOBODY with any scientific sense says the above quote.

I (and others of course) say what causes squirt, but in the end, reducing mass at the end of the shaft is by far the easiest and most prevalent way to reduce squirt

But in the end, there is a lateral force in play, and that force is dependent on th amount of shaft involved while the tip and ball is in contact. It's the transverse wave concept, which is the deterring factor of squirt. That's been the truth for a long time. It's most definitely a materials thing. But, the math equation is about mass.

Pm me if you want.

I am with Fred on this one.... "while tip and ball are in contact" also means that at slower speeds where contact time varies by tip hardness the tip also has an impact on squirt as it is a main factor in how long the tip stays on the ball.... Is it any wonder that there are so many different shafts and tips on the market if there is a synergistic possibility??

Now does swooping have the same effect as a flexible shaft on the deflection equation and would it have different effects based on different stiffness shafts? Sorry had to do it......