Measuring shaft deflection

[dr_dave]

If you understand this in engineering terms, then you'll know that "shaft end mass," though a simple thing to say, is not wholly correct.

Freddy,

I assume you are referring to the effect shaft stiffness has on "endmass," as described on the shaft endmass and stiffness resource page, but please correct me if I am wrong by explaining it or linking to a specific post that does.

Thanks,
Dave

 

[dr_dave]

Fred or Dave either one, would you care to explain why deflection is altered with chalk?

If there is not enough chalk on the tip and a miscue results, the amount of CB deflection is most definitely different. Or did you mean something else? If so, do you have video evidence or data you can share on this?

Should testing with and without chalk yield identical results if deflection is all that's being measured?

... as far as I know, assuming no miscues are occurring during the testing.

Regards,
Dave

 

[Cornerman]

Fred or Dave either one, would you care to explain why deflection is altered with chalk? Should testing with and without chalk yield identical results if deflection is all that's being measured?

I think the simplest answer is to examine the extreme. If the friction was too high, the cueball would stick on the cue tip longer and end up releasing at a less angle than expected. The simple proof is that this is exactly what causes skid shots: an overly high friction coefficient at the contact point, resulting in an angle of release of the object less than the normal cut angle.

If memory serves, my one time trying a rubber tip did exactly as described above. That was long before a low squirt cue ever came about.

How's that?

 

[ceebee]

It won't be long, before Guido Orlandi & I will have a mechanical shooting fixture, coupled with Video & measuring devices for gauging deflection & throw. I'm not sure which tournament we will show up with the machine... we'll let you know.

 

[qbilder]

If there is not enough chalk on the tip and a miscue results, the amount of CB deflection is most definitely different. Or did you mean something else? If so, do you have video evidence or data you can share on this?

... as far as I know, assuming no miscues are occurring during the testing.

Regards,
Dave

I am specifically referring to miscues. A miscue is essentially the cue tip:cue ball relationship mirroring that of the cue ballbject ball, correct? I understand the mass of the cue ball is different than the mass of the tip end of the shaft. So let's sub the cue tip with a marble.

If you use a marble as the cue ball, does your contact point of aim change on the object ball? Furthermore, does the direction the marble & ball follow after impact differ than if the marble were a cue ball? Isn't this akin to a miscue? The tip contacts the edge of the cue ball, causing the cue ball to deflect exactly away from contact point. It happens exactly the same way as the object ball deflects away from the cue ball on a cut shot.

Now add chalk. Everything changes. No longer are we testing deflection alone, correct?

 

[qbilder]

I think the simplest answer is to examine the extreme. If the friction was too high, the cueball would stick on the cue tip longer and end up releasing at a less angle than expected. The simple proof is that this is exactly what causes skid shots: an overly high friction coefficient at the contact point, resulting in an angle of release of the object less than the normal cut angle.

If memory serves, my one time trying a rubber tip did exactly as described above. That was long before a low squirt cue ever came about.

How's that?

BINGO!!!! This is precisely what I am referring to. This friction coefficient is not factored into the deflection testing, which seems shoddy or incomplete, for lack of better word. No chalk = pure(ish) deflection. Chalk = altered deflection. Excessive chalk = uncontrollably low deflection. Does this spectrum not indicate a variable that makes the LD testing we use inaccurate?

If deflection alone were the objective of the test, wouldn't the test need to remove the factor of friction?

 

[Cornerman]

Freddy,

I assume you are referring to the effect shaft stiffness has on "endmass," as described on the shaft endmass and stiffness resource page, but please correct me if I am wrong by explaining it or linking to a specific post that does.

Thanks,
Dave

The term should be "mass involved in the collision," or "effective mass." And please don't say it's easier to say "shaft endmass." If a cuemaker can effectively decouple a significant portion of mass from the collision dynamics, then that will reduce squirt. By calling it "endmass" or any variation, it gives a limited description to cuemakers who may want to expand on different concepts. Fortunately, someone lkie Royce wasn't so discouraged. Other cuemakers have no engineering background, so they might not try anything else other than drilling holes.

And this isn't new either. I have many decoupled and dampening concepts. I know Bob Jewett had discussed some low-friction slide bearing decoupling of the tip. Sounds crazy, but in my experience, crazy is how you make advancements. You can talk the science, and let guys like Royce figure out the execution (with the helps of materials and process guys like me).

After 20 years of discussing this, I'm surprised we still say "endmass." We're better than that.

 

[Cornerman]

It won't be long, before Guido Orlandi & I will have a mechanical shooting fixture, coupled with Video & measuring devices for gauging deflection & throw. I'm not sure which tournament we will show up with the machine... we'll let you know.

Charley, I'd be happy to give my input before you end up pulling a Bob Meucci. I develop these type of mechanical and electro-mechanical motion systems for my real-world living. And I think I understand the overall collision dynamics as well as anyone.

 

[dr_dave]

I am specifically referring to miscues. A miscue is essentially the cue tip:cue ball relationship mirroring that of the cue ballbject ball, correct? I understand the mass of the cue ball is different than the mass of the tip end of the shaft. So let's sub the cue tip with a marble.

If you use a marble as the cue ball, does your contact point of aim change on the object ball? Furthermore, does the direction the marble & ball follow after impact differ than if the marble were a cue ball? Isn't this akin to a miscue? The tip contacts the edge of the cue ball, causing the cue ball to deflect exactly away from contact point. It happens exactly the same way as the object ball deflects away from the cue ball on a cut shot.

Now add chalk. Everything changes. No longer are we testing deflection alone, correct?

The problem with a miscue is that it almost always involves secondary contact with the tip, ferrule, and/or shaft. See:

miscue resource page

So any comparison to an actual shot (with no miscue) is not very useful, IMO.

As long as there is chalk to provide enough friction to prevent a miscue, the action of the shot should be no different with different brands of chalk. For more info, see:

chalk comparison resource page

Enjoy,
Dave

 

[skankhammer]

Very interesting thread.

 

[qbilder]

The problem with a miscue is that it almost always involves secondary contact with the tip, ferrule, and/or shaft.

So if I were to cut a cue ball up and make a tip from it, never chalking it, it would result in hitting the cue ball more than once? Why would that happen with this scenario but not when the actual cue ball contacts an object ball?

I'm not being a PIA, just genuinely curious. I appreciate your willingness to discuss. Fred, too

 

[JC]

The problem with a miscue is that it almost always involves secondary contact with the tip, ferrule, and/or shaft. See:

I have always wondered why a miscue gets a pass from being a foul in the rules when it fits all the criteria. It's practically a text book definition of a foul stroke.

JC

 

[Cornerman]

So if I were to cut a cue ball up and make a tip from it, never chalking it, it would result in hitting the cue ball more than once? Why would that happen with this scenario but not when the actual cue ball contacts an object ball?

I'm not being a PIA, just genuinely curious. I appreciate your willingness to discuss. Fred, too

Let’s try it! I expect the non-miscue, cueball cue tip squirt results to be just slightly more than with traditional chalk, but maybe not significant.

And of course we can test for squirt without chalk. Just stay within a certain offset range.

 

[dr_dave]

I think the simplest answer is to examine the extreme. If the friction was too high, the cueball would stick on the cue tip longer and end up releasing at a less angle than expected. The simple proof is that this is exactly what causes skid shots: an overly high friction coefficient at the contact point, resulting in an angle of release of the object less than the normal cut angle.

If memory serves, my one time trying a rubber tip did exactly as described above. That was long before a low squirt cue ever came about.

How's that?

BINGO!!!! This is precisely what I am referring to. This friction coefficient is not factored into the deflection testing, which seems shoddy or incomplete, for lack of better word. No chalk = pure(ish) deflection. Chalk = altered deflection. Excessive chalk = uncontrollably low deflection. Does this spectrum not indicate a variable that makes the LD testing we use inaccurate?

If deflection alone were the objective of the test, wouldn't the test need to remove the factor of friction?

A tip-CB collision is very different from a CB-OB collision. With a tip-CB collision, there must be enough friction to prevent slip. If the tip slips, a miscue results. Having more than enough friction doesn't change anything. The tip either grabs, or it doesn't!

When a CB hits an OB, the ball surfaces slip during contact. They gear together at some point during contact (like the cue tip and CB) only for small cut angles or when sidespin on the CB is close to the gearing amount of outside english. Ball gearing is what creates the flat portions of many of the throw-effect graphs and some of the interesting (and non-obvious) throw effects (see items 16-38 in the numbered list).

Regards,
Dave

 

[dr_dave]

So if I were to cut a cue ball up and make a tip from it, never chalking it, it would result in hitting the cue ball more than once?

... I would think so if the CB is hit off center, assuming the CB "tip" is attached to a typical pool shaft and cue. BYW, you can easily simulate this by using a phenolic tip with no chalk.

Why would that happen with this scenario but not when the actual cue ball contacts an object ball?

... because a CB is not attached to a pool cue.

Regards,
Dave

 

[dr_dave]

I have always wondered why a miscue gets a pass from being a foul in the rules when it fits all the criteria. It's practically a text book definition of a foul stroke.

FYI, the miscue resource page addresses the reasons behind this, and describes and demonstrates some interesting examples where a miscue is and is not a foul.

Enjoy,
Dave

 

[JC]

FYI, the miscue resource page addresses the reasons behind this, and describes and demonstrates some interesting examples where a miscue is and is not a foul.

Enjoy,
Dave

Any time you hear the telltale clank of the ferule and the cue ball goes off in a sideways direction or jumps up off the table this must be a foul by definition. You struck it twice with your cue.

JC

 

[Cornerman]

Any time you hear the telltale clank of the ferule and the cue ball goes off in a sideways direction or jumps up off the table this must be a foul by definition. You struck it twice with your cue.

JC

Oddly enough, I’m opposite. I think if a miscue isn’t a foul, the double hits shouldn’t be either. If someone can control the double hit, more power to them.

Freddie <~~~ but that’s just me

 

[dr_dave]

Any time you hear the telltale clank of the ferule and the cue ball goes off in a sideways direction or jumps up off the table this must be a foul by definition. You struck it twice with your cue.

JC

Audio is not admissible evidence. Also, the CB would go off to the side even without a secondary contact. Also, a scoop shot doesn't necessarily involve secondary contact; although, it is always a foul. For more info and slow-mo video demonstrations, see the "scoop" jump shot foul resource page.

Regards,
Dave

 

[dr_dave]

Oddly enough, I’m opposite. I think if a miscue isn’t a foul, the double hits shouldn’t be either. If someone can control the double hit, more power to them.

I'm with you on this one. We have far too many rules that cause too much misunderstanding and misinterpretation, and some requiring judgement of "intent." If the rules would allow more things, the rules will be simpler and there will be far fewer arguments.

Regards,
Dave