banks and kicks

• advantages of fast speed
• diamond systems for kick shots
• double kiss detection and avoidance with bank shots
• effects and factors to consider
• mirror system for shallow-angle, rolling kick shots
• spin transfer bank shots
• spot-on-the-wall kicking system
• two-rail parallel-line kick shot
• two-times and three-times across side bank shots

for more information, see Chapter 6 and Sections 7.06-7.08 in The Illustrated Principles of Pool and Billiards
and Disc IV of the Video Encyclopedia of Pool Shots

advantages of fast speed

Why do many top bankers use fast speed?

With faster speed, there is much less variation from table to table and from shot to shot. The OB will pick up less roll, and this (combined with the post rebound speed) will minimize how much the OB curves after rebound. As a result the ball will bank in a more consistent direction. At slower speeds, the path and final target of the rebounding ball varies a lot with small changes in speed. The disadvantage of faster speed is the reduced effective "size" of the pocket.

Faster speed can also help reduce the chance for a double kiss at certain approach angles (see HSV B.34).

from Patrick Johnson:

Each bank shot is affected by many variables, each of which changes the angle of rebound:

stickiness of:
- rail cloth
- surface cloth
- balls
trueness of:
- rails
- surface
spin on OB:
- sidespin
- follow/draw

The holy grail in banks is to eliminate as many variables as possible, and just about every one of these variables "flattens out" at higher speeds. Shooting at one hard speed eliminates the most variables so you don't have to shoot the same bank differently each time.

diamond systems for kick shots

How does the Diamond System work?

The simplest diamond system is the 1-rail through-diamond system.

The most famous"diamond system" is the three-rail "Corner 5" system. It is illustrated and explained, with examples, in TP 7.2 and in these articles: part 1 and part 2. Here's another useful resource.

The three-rail Corner-5, two-rail Plus-2, and "spot-on-the-wall" systems are described and demonstrated in NV B.35.

Here's an article on the Plus-2 system.

from DeadAim:

complete "kicking academy" document describing and illustrating many diamond systems for kick shots.

double kiss detection and avoidance with a cross-corner bank shot

How do you know if a bank shot will cause a double-kiss, and how can you avoid it?

See NV B.23. The video demonstrates an easy method to use to detect and avoid cross-corner bank double kisses.

HSV B.32 shows several techniques to avoid a double kiss with a cross-side bank shot.

HSV B.34 shows how to detect a double kiss when banking a ball frozen or close to the rail.

effects and factors to consider

What effects does one need to adjust for when aiming bank and kick shots?

The basic mirror (angle in equals angle out) systems provide a point of reference only. Your aim with a given shot depends on many effects. The effects that require aim adjustment include:

• In general, more speed shortens the rebound (see NV 6.6), and less speed lengthens the rebound (see and NV 6.7); however, see HSV B.41.
• Less ball topspin roll (due to faster speed or closeness to rail) means shorter rebound.
• Running English lengthens rebound, reverse English shortens it (see NV 6.8). This effect is greatest with the ball heading straight into the rail (i.e., with no approach angle)
• Follow lengthens kick rebound, draw shortens it (e.g., see NV B.29 and NV B.57).
• English has little effect at large approach angles, where the ball is heading fairly parallel to the rail. However the English will have a large effect off the second rail, where the approach angle will be small, with the ball heading fairly perpendicular to the rail.
• An outside cut shortens a bank (see NV 6.12), an inside cut lengthens it (see NV 6.13).
• bank direction consistency is generally better at faster speeds
• Spin transfer can significantly affect banks (e.g., left English on the CB can transfer right spin to the OB which shifts the rebound to the right).
• Cut and spin transfer effects are related to throw effects, so a complete understanding of throw helps too.

If one doesn't understand all of these effects, or have great intuition built up from years and years of experience (i.e., lots of mistakes and successes), the mirror systems are not very useful.

For kick shots with small approach angles (i.e., almost straight into the rail), it sometimes helps to know how topspin and bottom-spin change off the rebound. For more information and examples, see:

• HSV A.117 - straight-on kick shot at fast speed with follow, stun, and draw
• HSV A.118 - straight-on kick shot at slow speed with follow, stun, and draw
• HSV A.119 - straight-on kick shot of a polished ball at fast speed with follow, stun, and draw
• HSV A.120 - straight-on kick shot of a polished ball at slow speed with follow, stun, and draw
• HSV B.15 - straight-on kick shot rebound losses and spin changes for roll, stun, and draw shots
• NV B.18 - Kick shot cue ball hold shot example with Tom Ross
• NV B.27 - Rail-first draw kick safety, with Tom Ross

from Patrick Johnson:

For kicks the important thing is what kind of "vertical spin" the CB has on it when it hits the rail:

- CB sliding when it hits the rail will rebound with no curve at the "mirror angle" (minus something for rail friction)

- CB with forward spin (including natural roll) when it hits the rail will curve longer than the mirror angle

- CB with backspin when it hits the rail will curve shorter than the mirror angle

How much longer or shorter the CB rebounds (with forward spin or backspin) depends on how much spin is on the CB* and how much friction there is between the CB and the cloth.

For banks the important thing is how much vertical spin is on the OB when it hits the rail. This can only be controlled by hitting harder or softer (harder = less or no forward spin; softer = more forward spin). This is also why hitting harder shortens bank angles.

*: How much spin is on the CB depends on: - how hard it's hit - how high it's hit - how far it is from the rail when it's hit - how much friction there is between CB/cloth

As this drawing shows, when the CB changes direction off the rail its spin does not change direction. That means that forward or reverse spin which was rotating parallel with the CB's path before hitting the rail is rotating across the CB's path after hitting the rail - this across-the-path rotation is what causes the CB to curve after hitting the rail.

Forward rotation (topspin) can be the result of the CB rolling naturally or of hitting high on the CB. Reverse rotation (backspin) can only be the result of hitting low on the CB.

Concerning HSV B.41, why doesn't speed shorten the rebound angle? Doesn't the ball compress the cushion sideways more at higher speed, and wouldn't that create sideways forces that would shorten the rebound angle?

There are many physical effects that control the immediate rebound angle and the amount of masse curving after rebound. I use the phrase "rail throwback" to refer to the effect you are describing. With more speed the cushion deforms more and can generate more sideways force to shorten the angle; however, the rebound angle is also affected by the efficiency (coefficient of restitution = COR) of the cushion, and this can vary with speed and angle also. Based on the results in HSV B.41, I think these two effects are balancing each other out. The rail throwback effect tries to shorten the rebound angle and the efficiency effect apparently tries to lengthen the rebound (because the cushion is returning less energy, maybe partly because of the ball shift down the rail). This is all conjecture, but I think it makes sense physically. There are also friction effects between the ball and cushion and ball and table during impact. These might also vary in complicated ways with speed.

mirror system for shallow-angle, rolling kick shots

Does the basic mirror system apply for shallow angle, rolling kick shots?

from Bob_Jewett:

The "bounce" for a shallow-angle rolling shot is only about 70% of the incoming angle. That is, the ball tends to go more parallel to the cushion than the mirror system says. How much of the 30% discount applies depends on the spin and speed on the cue ball, of course.

spin transfer bank shots

Is spin transfer required to make certain bank shots?

Yes. See NV B.20 for two important examples. For more information, and another example, see my March '07 article.

spot-on-the-wall kicking system

How do "spot-on-the-wall" kicking systems work?

The three-rail Corner-5, two-rail Plus-2, and one-rail kick "spot-on-the-wall" systems are described and demonstrated in NV B.35.

two-rail parallel-line kick shot

Dr. Dave, I have been practicing the 2-rail parallel line kick shots you show in your book on pages 229 & 230 and demonstrated in NV 7.9. It works fine if I set up the balls similar to what you show in your book but I am having difficulty envisioning the same shot from other set ups. I don't think I fully understand how to determine the center line between the 2 parallel lines. Can you elaborate on this idea?

Unfortunately, the action of this shot depends on English (running vs. reverse), shot speed, and table (especially cushion) conditions. Obviously, when practicing, you need to try to use consistent English and speed on a given table to see how the cue ball responds at different angles.

Concerning how to aim, I usually do a trial and error sort of thing where I first take a guess at the aiming line direction, lining up the cue stick through the cue ball in this direction. Then I visualize the direction the cue ball will come of the first rail. For a medium speed, center ball hit, the angle off the rail is close to the angle into the rail. This lets me estimate where the cue ball will hit the second rail. Moving the cue stick to that point, keeping it parallel to the initial aiming line, will estimate the final direction. Then I adjust the aiming line direction as necessary based on how the estimated final direction compares with the desired target direction. I continue this until I am happy with the final direction. This goes quickly after you get the hang of it. Also, the final line will usually come up a little short (e.g., see Figure 7.21 on p. 230), so I adjust my aim a little to account for this; but again, this will depend on the table conditions and how you shoot the shot. If you use running English, you will also need to get a feel for how it affects the angle off the first rail.

I know all of that sounds complicated, but I hope it helps some. I, for one, don't expect to have great accuracy with this type of shot. Although, it comes in handy when I get badly snookered by a well-played opponent safety or by very poor position play on my part.

Bob_Jewett wrote:

... the "Amazing Double-mirror Image Method" or ADIM for short ... is explained on the second page of http://www.sfbilliards.com/articles/2004-07.pdf. Mostly, it gives you a very easy way to put up a target ball exactly where the real ball would appear for a perfect mirror system. ... This lets you see immediately how pitifully awful the two-rail mirror system is, but it also allows you to try to find out where it does work and maybe how to modify it so it works for more cases.

two-times and three-times across cross-side bank shots

What are "two-times" and "three-times" across bank shots, and how do they work?

See: NV B.22 - Two-times and three-times across bank shots.

from Patrick Johnson:

It's a series of spin events:
1. The CB colliding with the OB puts some "holdup" spin on the OB, which shortens the angle off the first rail.
2. The OB colliding with the first rail at an angle reverses the spin that was put on by the CB (just like any ball picks up "running" spin when it hits the rail).
3. The reversed spin throws the OB toward the side pocket off the second rail.