does drawing the cb shorten up an ob bank because the cb draw transfers follow to the ob?
quick banking question
- Thread starter evergruven
- Start date
Follow on the OB (when it’s rolling) lengthens the rebound, not shortens it. Putting significant follow on the OB by using draw on the CB is unlikely.
pj
chgo
I agree with the first part, but rail compression due to speed has nothing to do with the ball going shorter. This is easy to demonstrate. It is the lack of follow on the OB on fast shots that causes it to bank shorter. This is a common misconception.
In fact, didn't you post a video with Dr. Dave some time back that showed, comparing two sliding OBs, the one hit harder rebounds slightly long because it rolls along the rail more?
pj
chgo
Colour me misconcepted...lol
Not really much of a student in banking I really shouldn't commented at all. However, I definitely glad I did. Officially learnt something today. Thanks...
That effect is small -- like an inch in a table width -- on some tables but mostly an object ball without spin will bank to the same spot regardless of the speed it has. I found that snooker cushions -- which have a very different shape for the rubber -- tend to bank longer for harder shots.
Here is a diagram from Byrne's 1990 book "Advanced Technique" that illustrates the main point of the speed/bank angle connection. Playing the combo bank that is far from the cushion is very speed dependent. The combo bank that is close to the cushion is not speed dependent if the banking ball is close enough to the rail that it does not acquire follow on the way to the rail.
I find it remarkable and discouraging that so few good pool players have actually studied the game. This particular point has been available in a clear, concise, convincing explanation for over 30 years and yet the "rail compression" fable continues to circulate.
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Well now you're just making me feel bad....
I do make an effort not to play bank shots, so again I haven't dug into the dynamics. The fact that the misconception of rail compression vs the reality of dead OB interaction manifests into the same expected result kinda makes the lesson learnt moot from a practical stand point I think. Always good to know how things actually work but in this case it really changes nothing. At least not for me
I found a good explanation of banking in "A Pool Lesson with Jerry Briesath". He explains that when a ball is sliding into a rail, the rebound angle into the rail is matched by the rebound angle coming off the rail--as you might (wrongly) expect would be true of all banks. Balls that are close to a rail, or balls that are a long distance from the rail but that are hit hard enough, will slide into the rail. For sliding balls, you use the position on the cushion directly in front of the diamonds to aim your banks. For instance, the 3 to 1.5 track would be the track measured from the point on the cushion in front of diamond #3 to the point on the cushion in front of diamond #1.5:
On the other hand, if a ball is rolling or has topspin when it hits a rail, then things work differently. Jerry Brieseth set up a video camera to demonstrate what happens. The video reveals that a ball rolling ball into a rail will rebound off the rail and slide for some distance, then the topspin will take, making the ball curve in the direction of the topspin. As a result, the topspin will make the ball curve long. In the video, you can clearly see how a ball that is rolling when it hits the rail curves after it hits the rail. Therefore, the angle into the rail no longer equals the angle off the rail, hence the need to adjust. You have to adjust by aiming at a spot short of the spot on the cushion that is directly in front of the diamond. One method of adjusting is to use the diamonds themselves as the aim points, rather than the spot on the cushion directly in front of the diamonds. When you aim at a diamond, the actual contact point on the cushion will be short of the point on the cushion directly in front of the diamond:
There is no rhyme or reason to aim at the diamond--it's just a random amount of adjustment that's in the direction needed (shorter). In the end, you still have to figure out how much adjustment is needed for the table, e.g. you may need to aim even shorter than the diamond aim point, so that when the ball rebounds off the rail and curves, it will end up where you want it.
Another interesting thing he talks about is cloth speed. For new cloth, he says that when the ball impacts the rail, the rail will not rub off much of the topspin, while with old cloth the rail will rub off more of the topspin. Therefore, depending on the condition of the cloth, a ball that rolls into a rail will require different amounts of adjustment. He says that is why pros always hit their banks hard: a sliding cue ball needs no adjustment--the angle into the rail equals the angle leaving the rail--no matter the condition of the cloth.
He also says that balls rolling into a rail at shallow angles will hit the rail closer to the axis of rotation, which does not rub off as much spin, so shallower angles cause the ball to curve even more after hitting the rail, effectively increasing the exit angle, so more adjustment is needed for balls that roll into the rail at shallower angles. In other words, as the bank angle gets larger and larger, you have to adjust to hit the rail shorter and shorter than the point on the cushion directly in front of the diamond.
Perhaps Bob Jewett can comment on how much of that is born out by the physics.
In the end, I realized there is no "system" for banking if the ball is rolling when it hits the rail. Instead, you have to adjust for:
1. How much topspin the ball has when it hits the rail. The more topspin, the more the ball curves longer after hitting a rail.
2. Steep v. shallow angles. The shallower the angle, the more a rolling ball curves longer after hitting a rail.
3. Fast or slow cloth. The faster the cloth, the more a rolling ball curves longer after hitting a rail.
Dr. Dave has a great video on the effects of topspin, draw, and speed when you hit the cue ball into a rail:
Of course, you also have to be aware that a bank will go longer or shorter due to sidespin (cut induced or throw induced).
On the other hand, if a ball is rolling or has topspin when it hits a rail, then things work differently. Jerry Brieseth set up a video camera to demonstrate what happens. The video reveals that a ball rolling ball into a rail will rebound off the rail and slide for some distance, then the topspin will take, making the ball curve in the direction of the topspin. As a result, the topspin will make the ball curve long. In the video, you can clearly see how a ball that is rolling when it hits the rail curves after it hits the rail. Therefore, the angle into the rail no longer equals the angle off the rail, hence the need to adjust. You have to adjust by aiming at a spot short of the spot on the cushion that is directly in front of the diamond. One method of adjusting is to use the diamonds themselves as the aim points, rather than the spot on the cushion directly in front of the diamonds. When you aim at a diamond, the actual contact point on the cushion will be short of the point on the cushion directly in front of the diamond:
There is no rhyme or reason to aim at the diamond--it's just a random amount of adjustment that's in the direction needed (shorter). In the end, you still have to figure out how much adjustment is needed for the table, e.g. you may need to aim even shorter than the diamond aim point, so that when the ball rebounds off the rail and curves, it will end up where you want it.
Another interesting thing he talks about is cloth speed. For new cloth, he says that when the ball impacts the rail, the rail will not rub off much of the topspin, while with old cloth the rail will rub off more of the topspin. Therefore, depending on the condition of the cloth, a ball that rolls into a rail will require different amounts of adjustment. He says that is why pros always hit their banks hard: a sliding cue ball needs no adjustment--the angle into the rail equals the angle leaving the rail--no matter the condition of the cloth.
He also says that balls rolling into a rail at shallow angles will hit the rail closer to the axis of rotation, which does not rub off as much spin, so shallower angles cause the ball to curve even more after hitting the rail, effectively increasing the exit angle, so more adjustment is needed for balls that roll into the rail at shallower angles. In other words, as the bank angle gets larger and larger, you have to adjust to hit the rail shorter and shorter than the point on the cushion directly in front of the diamond.
Perhaps Bob Jewett can comment on how much of that is born out by the physics.
In the end, I realized there is no "system" for banking if the ball is rolling when it hits the rail. Instead, you have to adjust for:
1. How much topspin the ball has when it hits the rail. The more topspin, the more the ball curves longer after hitting a rail.
2. Steep v. shallow angles. The shallower the angle, the more a rolling ball curves longer after hitting a rail.
3. Fast or slow cloth. The faster the cloth, the more a rolling ball curves longer after hitting a rail.
Dr. Dave has a great video on the effects of topspin, draw, and speed when you hit the cue ball into a rail:
Of course, you also have to be aware that a bank will go longer or shorter due to sidespin (cut induced or throw induced).
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The main situation where it makes a difference is when you are banking a ball near a cushion. Softly does not make it go longer. If the bank shot is a diamond or more from the cushion, then you will see the soft/hard difference but it will not be because of rail compression. It will be due to the forward roll on the object ball.
If you never bank balls that are close to the cushion softly then I agree that you are not affected by this.
This is not true. It's easy to test, but you have to be careful in how you set up the test if you want accurate results. A sliding ball banks about 25% short relative to a true mirror reflection at the rail groove.
Wow! So, you actually need to aim longer (than the spot on the cushion in front of a diamond) when the cue ball is sliding? Do Diamond v. Brunswick cushions vary in that regard?
Does a sliding ball with gearing sidespin bank at the equal angle? Is that speed dependent?
pj
chgo
In terms of the 25% number, they're probably similar but 28% and 23% would be huge to an actual banks player. If you wanted to actually measure the difference, it would be complicated. Both tables set up as from the factory and with the same type and age of cloth, etc. It might be easier to measure a bunch of tables in the field and give statistics and maybe more useful as well but it would be a lot of work.
I think it's going to be close to equal, and that is what Ron Shepard's kicking system is based on, but I've never done a test that could tell how much it's off. It is guaranteed to be off some. Rail contact is very, very complicated. The rail deforms and then all of the simple ideas are overwhelmed by the details.
I think it leaves everyone out in a sense. It's like a lot of other parts of pool. A system will give you a framework and experience will fill out the framework. In the end you have to go by feel. The actual nitty physical details are just covered by the experience.
I know some banks tighten or shorten up better if I use follow instead of draw. Probably because the ob slides more and hits the cushion without much forward roll. But then again, it could all be in my head. That's how a lot stuff works in this game -- we do something different and associate what we did with the results we get, when in reality it's likeky something else occurring that allows those results, like something we're doing with the stroke.
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Never is a strong word... I won't say never but it's usually extremes. Soft rolls that are close like you suggest, or hard skidding banks that I try to shorten up.
Banks for me are a necessary evil. Usually I'll play patterns around them and more often than not only take them on if it's do or die.
I'm fairly decent at banks as compared to a typical pool player. I have no measureable skill in the department however.