Science Schmience: CB Follow/Draw for Banks

[gulfportdoc]

... P.S. To be clear: my point is not that transferred follow (or draw) never affects the bank path - it's that it only affects the bank path in certain limited circumstances, and only to a small degree even then.

Fascinating stuff, Patrick. One can't argue with practical physics. The distance from OB to rail is the key, then; and of course how much reverse spin on the CB when it contacts the OB. The question is to arrive at a rule of thumb. It would be easy for practical knowledge to measure, say, for a common 2 to 1 bank, e.g. side pocket to middle diamond to corner pocket, and different OB & CB lengths with different speeds.

I'd like to see Mike Page's excellent video replicated, only with underspin. And how long different rotations of underspin affect the OB. Perhaps he's already done this.

BTW, John B. is right. This thread should be in the bank pool section. But Steve would have to move the entire thread.

~Doc

[mr3cushion]

I'm just sitting here wondering, what "Bugs" and "Taylor" would have to say about ALL this!

Who were concidered the two GREATEST bankers of ALL time!

[Patrick Johnson]

I'm just sitting here wondering, what "Bugs" and "Taylor" would have to say about ALL this!

Who were concidered the two GREATEST bankers of ALL time!

They'd probably say, "when I do this, that happens, and here's why". Of course they'd be right about what happens, but even money they'd be wrong about why. A good example of this is the common wisdom that hitting banks harder makes them go shorter. That's true, but the common explanation that they bank shorter because of more rail compression is wrong. In fact, absent other effects, more rail compression makes the OB bank a little longer, as shown by Bob Jewett:

Video: Bank Speed Effects, with Bob Jewett

The more likely explanation is that at slower speeds the OB gets rolling before hitting the rail, which makes it curve longer than equal-angle after rebounding. And at faster speeds the OB slides into the rail (with less or no forward rotation), which makes it bank closer to equal-angle.

So the real explanation is not that banking harder shortens banks, but that banking softer lengthens them. That might sound like nitpicking, but knowing what's really happening can matter - for instance, it tells you that you probably won't shorten a bank by hitting it harder if the OB is too close to the rail to get rolling anyway.

pj
chgo

[mr3cushion]

They'd probably say, "when I do this, that happens, and here's why". Of course they'd be right about what happens, but even money they'd be wrong about why. A good example of this is the common wisdom that hitting banks harder makes them go shorter. That's true, but the common explanation that they bank shorter because of more rail compression is wrong. In fact, absent other effects, more rail compression makes the OB bank a little longer, as shown by Bob Jewett:

Video: Bank Speed Effects, with Bob Jewett

The more likely explanation is that at slower speeds the OB gets rolling before hitting the rail, which makes it curve longer than equal-angle after rebounding. And at faster speeds the OB slides into the rail (with less or no forward rotation), which makes it bank closer to equal-angle.

So the real explanation is not that banking harder shortens banks, but that banking softer lengthens them. That might sound like nitpicking, but knowing what's really happening can matter - for instance, it tells you that you probably won't shorten a bank by hitting it harder if the OB is too close to the rail to get rolling anyway.

pj
chgo

I only have one question. Why is Bob demonstrating this by playing a, "combination" bank, instead of the CB to OB directly?

[Patrick Johnson]

I only have one question. Why is Bob demonstrating this by playing a, "combination" bank, instead of the CB to OB directly?

To avoid small aiming and sidespin errors, which would make the results impossible to interpret accurately. Anticipating and controlling variables like that is one of the reasons we can trust the results of tests done by "scientists" like Jewett, Page, etc. over the "personal experience" of (even very good) players.

pj
chgo

P.S. To be clear about this aside: CB/OB spin transfer (the topic of this thread) is not what Bob was testing - he was testing the effect of speed alone, so he wanted to avoid any CB spin transfer.

[mr3cushion]

To avoid small aiming and sidespin errors, which would make the results impossible to interpret accurately. Anticipating and controlling variables like that is one of the reasons we can trust the results of tests done by "scientists" like Jewett, Page, etc. over the "personal experience" of (even very good) players.

pj
chgo

I have MANY more Q's, but this would turn into another debacle!

I'll leave it alone!

[John Brumback]

They'd probably say, "when I do this, that happens, and here's why". Of course they'd be right about what happens, but even money they'd be wrong about why. A good example of this is the common wisdom that hitting banks harder makes them go shorter. That's true, but the common explanation that they bank shorter because of more rail compression is wrong. In fact, absent other effects, more rail compression makes the OB bank a little longer, as shown by Bob Jewett:

Video: Bank Speed Effects, with Bob Jewett

The more likely explanation is that at slower speeds the OB gets rolling before hitting the rail, which makes it curve longer than equal-angle after rebounding. And at faster speeds the OB slides into the rail (with less or no forward rotation), which makes it bank closer to equal-angle.

So the real explanation is not that banking harder shortens banks, but that banking softer lengthens them. That might sound like nitpicking, but knowing what's really happening can matter - for instance, it tells you that you probably won't shorten a bank by hitting it harder if the OB is too close to the rail to get rolling anyway.

pj
chgo

I agree with all of this also. I try to be very careful about what I tell people about pool and banking. You would never hear me say that you have to shoot hard to shorten or hold a bank shot. That's just another old myth On top of that...if you shoot too hard ( with low) the oball will bounce and go even longer I try not to get into the science part of a pool shot but I do feel that I know what works good and what doesn't. I can show better than I can tell is what I'm saying John B.

[gulfportdoc]

... A good example of this is the common wisdom that hitting banks harder makes them go shorter. That's true, but the common explanation that they bank shorter because of more rail compression is wrong. In fact, absent other effects, more rail compression makes the OB bank a little longer, as shown by Bob Jewett:
Video: Bank Speed Effects, with Bob Jewett ...
pj
chgo

My guess is that the "shortness" varies depending upon the angle coming into the rail. Obviously a wide angle bank is not going to come "short", whereas a medium angle bank would appear to. It would be interesting to know at what angle there is no effect.

And, conversely, at what angle the "long" effect dissipates.

~Doc

[Patrick Johnson]

My guess is that the "shortness" varies depending upon the angle coming into the rail. Obviously a wide angle bank is not going to come "short", whereas a medium angle bank would appear to. It would be interesting to know at what angle there is no effect.

And, conversely, at what angle the "long" effect dissipates.

~Doc

I "measure" my banks and kicks using the diamonds. The equal-angle rail contact point is always at the "gutter" in front of the rail, but most banks/kicks (at moderate speed with no spin) must be aimed shorter than that because they tend to go long (because of forward rotation and because the rail doesn't "give back" all the speed it absorbs).

Aiming at the diamonds on the rail rather than at the equal-angle spot at the gutter does a fair job of adjusting for this, even automatically "adjusting the adjustment" - shortening the angle more for wider angles and less for steeper ones. I find that when the angle gets very wide or very steep I need to add some manual adjustment too - aiming behind the diamond on the rail for wider angles and in front of it (but still on the rail) for steeper ones.

I think no adjustment (aiming right at the equal-angle gutter spot) isn't possible except for very steep angles, probably less than 10 degrees (like kicking cross corner from 1 diamond up the long rail).

pj
chgo

P.S. Here's a checklist of some things that affect rebound angles. Some of these work against each other, sometimes cancelling both effects.

- rail "rebound efficiency" (coefficient of restitution) is less than 100%, causing balls to rebound long - most effect at 45 degrees(?)
- rail friction (between cloth and ball) causes balls to rebound short - most effect at 45 degrees(?); effect increased by sticky cloth balls
- "rolling follow" masse causes balls to curve long after rebounding - most effect at 45 degrees; effect increased by sticky cloth balls
- shot speed causes balls to rebound longer at lower speeds and shorter at higher speeds, because of the presence or absence of rolling follow
- draw masse causes balls to curve short after rebounding - most effect at 45 degrees; effect increased by sticky cloth balls
- rail-induced masse causes balls to curve short after rebounding - most effect at 45 degrees(?); effect increased by sticky cloth balls
- left/right sidespin causes balls to rebound longer (if "running" spin) or shorter (if "braking" spin) - most effect at steep angles; effect increased by sticky cloth balls

[gulfportdoc]

I "measure" my banks and kicks using the diamonds. The equal-angle rail contact point is always at the "gutter" in front of the rail, but most banks/kicks (at moderate speed with no spin) must be aimed shorter than that because they tend to go long (because of forward rotation and because the rail doesn't "give back" all the speed it absorbs).

Aiming at the diamonds on the rail rather than at the equal-angle spot at the gutter does a fair job of adjusting for this, even automatically "adjusting the adjustment" - shortening the angle more for wider angles and less for steeper ones. I find that when the angle gets very wide or very steep I need to add some manual adjustment too - aiming behind the diamond on the rail for wider angles and in front of it (but still on the rail) for steeper ones.

I think no adjustment (aiming right at the equal-angle gutter spot) isn't possible except for very steep angles, probably less than 10 degrees (like kicking cross corner from 1 diamond up the long rail). ...

I too have always used the diamonds as aiming points, probably because I played 3C years ago. I've noticed that purely aiming at the diamonds doesn't allow for equal angle systems for banks-- not lending itself to such a neat system as does the "diamond system" in 3C. But that's another subject. Although, maybe not, due to the rebound angle from wider/shorter approaches.

When you aim at the gutter in front of the rail, are you referring to where the rail meets the table bed? I noticed that Fred in his banking book uses the point on the rail exactly opposite the diamond (at least for many shots), which is a half inch or so ahead of the juncture, depending upon the angle of approach. Actually if you played on a Diamond table rather than a GC, you might find that your aim point is right on, rather than having to move back a little, since Diamond tables tend to rebound shorter than do GC's. At least the red label tables did.

~Doc

[Patrick Johnson]

When you aim at the gutter in front of the rail, are you referring to where the rail meets the table bed?

I mean the worn track parallel to the nose of the rail a little less than half a ball out from it (made by balls being forced down as they rebound), where the center of the ball changes direction. It's a conveniently visible spot (unless the cloth is new) to visualize as the apex of the ideal equal-angle rebound.

If you want to get real precise, remember that the ball compresses the cushion and slides/rolls along it a short distance while it's rebounding, "rounding off" the point of that ideal equal angle. So the actual apex of the equal angle is closer to the cushion nose itself.

Of course, this is all about using ideal equal angles as references because they can be quickly and objectively measured - balls rarely follow the equal angle path exactly.

pj
chgo

[John Brumback]

pj, Three things. 1. We are talking about hitting the cue ball with draw and this having an effect on the path of a banked object ball.
2. Your stroke makes a difference. There are strokes and there are strokes. You need a stroke to show any truth here.
3. Momentary is enough. Like a soft masse, momentary English taking can change the path of the ball.

"Momentary is enough". Wise words if you ask me. John B.

[John Brumback]

Doesn't matter if it's close to the rail or out in the middle of the table. John B.

[petie]

If 'roll' or English induced by the ball rolling on the cloth nullified English, it would, it seems, nullify left or right English as well. It doesn't seem to though. Shoot a long hold-up bank and you can see that there is plenty of hold-up English to shorten the angle of the bank quite a bit even after the ball has traveled the length of the table to get to the rail.

[straightback]

Doesn't matter if it's close to the rail or out in the middle of the table. John B.

It certainly does for banks hit with a slower pace. For banks played at typical bank pool cinch speed, it does not.