Dr. Dave's answers to frequently-asked questions (FAQs), mostly from the AZB discussion forum
for more information, see Chapter 4 in The Illustrated Principles of Pool and Billiards,
Vol. II of the Video Encyclopedia of Pool Shots,
and Vol. I of How to Aim Pool Shots (HAPS)
What is a drag shot, and how does it affect sidespin?
A drag shot is one where CB sliding (from bottom spin, stun, or topspin less than full natural roll) is used to slow the CB on the way to the OB, resulting in the desired amount of draw, stun, or follow at the OB. As the CB drags across the cloth, any backspin gradually wears off, resulting in stun, and then the CB gradually develops complete forward roll. Here's an illustration (from Patrick Johnson) that shows how backspin gradually transforms to stun and then natural roll:
The following videos provide good illustrations of the "drag" action of the cloth:
Drag shots are used to:
For drag shots with sidespin, very little sidespin is lost as the CB slows. This intensifies the effect of the sidespin. Here are some examples from Vol. II of the Video Encyclopedia of Eight Ball (VEEB):
For more information, see "VEEB - Part III: Drag-Enhanced Sidespin" (BD, January, 2016).
And here's another example:
Here's a related video for getting quick draw: NV B.25 - Using draw and english to beat a scratch in a side pocket, with Tom Ross.
The ideal tip contact point to get the largest effective sidespin is illustrated in the diagram below from Vol. IV of the Video Encyclopedia of Pool Shots (VEPS). It is at the intersection of the miscue-limit circle (black) and the base circle (red) of equal size going through the center and resting point of the CB. The tip isn't as far from the vertical centerline of the CB as it would be at the miscue limit on the horizontal centerline (equator) of the CB, so the initial spin won't be maximum; but the drag action created by the bottom spin increases the effective amount of sidespin due to the slowing of the CB. This tip contact point results in the largest effective sidespin only after all backspin has worn off and the CB has developed full roll. At that point the CB will have more effective sidespin than is possible with any other hit. Shot 501 in VEPS-IV demonstrates the effect at the table, and TP B.17 provides a math/physics-based proof.
Cloth drag can also have a large impact on draw and follow shots, with and without sidespin. For more info, see:
For more information on cloth conditions effects, see the cloth effects resource page.
Why is it easier to hit a stop shot than to draw or follow the CB a precise amount?
A stop shot can withstand a small amount of back or top spin with no or little CB motion; and at faster speed, the CB is close to sliding over a very large distance, resulting is stop action. With follow and draw shots, especially at faster speed, small changes in the amount of spin (top or bottom) have large effects on CB travel distance. So a stop shot has a much larger margin for error.
examples of english shots
What are some good example shots where english (sidespin) is required?
Here are a good collection of example english shots from the BU Summer School Boot Camp. Demonstrations of most of these shots are in the following video (mostly near the end):
Many game-situation sidespin examples, strategies, and techniques are demonstrated in detail in the following instructional videos:
Why do some people like to use inside english, even on shots where it is not required for position?
First of all, the type of english is usually dictated by cue ball position requirements for the next shot, so inside english will not always be the right choice. Otherwise, here are some possible reasons to favor inside english (IE) when other english is not required (or when no english is required):
For more information, see "Throw - Part VII: CIT/SIT combo" (BD, February, 2007), the throw resource page, and the squirt, swerve, and throw effects summary page.
Why does IE increase throw at small cut angles and decrease throw at larger cut angles?
Let's start with a very small cut angle to the right, but almost straight. With no sidespin, the amount of throw will be very small and to the left slightly. With inside (right) sidespin, the OB will throw to the left a lot more; and with outside (left) sidespin, the CB will throw to the right. So in this case (a small cut angle), inside english obviously increases throw.
With larger cut angles, outside english can create throw either right or left based on whether the amount of english is greater than or less than the "gearing" amount. The following video demonstrates this effect:
HSV B.33 - Outside english gearing, and cut and spin-induced throwInside english always throws the OB in the same direction because the spin is in the CIT direction. However, CIT and SIT don't add like some people might think. The following article provides explanations, illustrations, and examples:
"Throw - Part VII: CIT/SIT combo" (BD, February, 2007)
At small cut angles and small amounts of sidespin, the CB and OB sort of stick together during contact. However, at larger cut angles and/or with lots of inside english, the CB is sliding against the OB during contact. Friction (and therefore throw) is less when the sliding speed is greater. That's why throw is actually less when you add inside with a larger cut angle, because spin increases the sliding speed during contact.
The following video demonstrates most of the important throw effects, showing how throw (CIT or SIT) varies with angle, speed, and the amount and direction of spin:
NV B.86 - Cut-induced throw (CIT) and spin-induced throw (SIT), from VEPS IVFor detailed explanations, illustrations, and examples of all throw-related effects, see the article and video links in items 15-36 under the videos here:
squirt, swerve, and throw effects
Is inside english a better choice than outside english to limit CB sideways drift on some shots?
See the following two videos that study this effect:
Also see the outside-english CB hold resource page.
from Colin Colenso:
Inside english is often useful in taking the CB 2 or 3 rails. Often in these situations it heads for open space into the middle of the table. With a little practice this is quite predictable and leaves a player better next shot options.
For the draw with inside they may be doing this to check (hold) the CB angle off the rail. It may allow them to hit the shot a bit firmer without risking losing the CB, and by hitting it a bit harder, they avoid the risk of leaving whitey too close to the rail.
Also, inside can be very useful in getting the CB down table from say a 3/4 ball shot down the long rail.
Inside has similar throw to rolling follow so long as you don't play it too soft or from too straight on. Advanced players often utilize it. Intermediate players seem to love their OE, whereas advanced players are often weary of it, other than using a touch to gear away the throw, particularly on soft stun shots.
Why are inside-english shots more difficult for some people?
from Patrick Johnson:
It's a combination of things:
1. You use it less often (partly because you're not as good with it).
2. You use it for different (often more difficult) shots.
3. You use different spin with it (usually high vs. usually center or low).
4. You hit it at a different speed (usually harder).
5. It's less self-correcting.
Pay attention to these things while practicing inside and outside shots and you'll get better at inside pretty quickly.
A specific suggestion: pay attention to exactly where your stick is pointing on each shot compared with the CB/OB contact points - as you make and miss shots it will help you see the exact differences in how to aim them (it also helps generally to build accurate "shot memory").
How can I get more english on the cue ball?
In general, to get maximum english, prepare and chalk a good tip, and hit the cue ball as far left or right of center as you can without miscuing. A striped ball can useful for practice because the width of the stripe is usually half the ball's diameter, and the edges of the stripe border the typical miscue limit (at half the ball's radius from center). Here's a useful illustration of maximum (100%) english:
For more information, see:
Maximum tip-offset considerations also apply to follow and draw shots. See "How High or Low Should You Hit the Cue Ball?" (BD, September, 2011) for more info.
Now, to achieve the most effect from sidespin (i.e., get the most rebound angle change off a cushion), you want to use a drag shot where you start the CB off with backspin, and the backspin wears off on the way to the cushion. The problem with hitting below center is that you must decrease the amount of sidespin (tip offset) a little. However, because the drag action slows the cue ball while retaining most of the sidespin, the rebound angle will be larger. For more info, see the drag shot resource page.
Some people think low-squirt shafts or tip type/brand or other things can help you get significantly more spin on the CB, but this is not the case. For more info see:
When using a very heavy and/or stiff cue, the maximum tip offset (and maximum spin) possible with a good hit can be more limiting than normal. As shown in the plots on pages 7 and 8 in TP A.30, with a hit close to the miscue limit, the CB might not separate from the tip fast enough. Also, with a stiff shaft (e.g., a carbon fiber shaft) the end of the cue won't deflect away from the ball as much as normal and will tend to flex back toward the CB faster (see cue vibration for video illustrations). These effects can result in a double hit or push that might not even be directly noticeable; although, the CB will squirt more than expected (as with a miscue shot). The 2nd-to-last shot (before the miscue) in HSV A.106 visually shows how close the tip can come to a double hit even with a typical-weight LD shaft, which is not very stiff. For more info on this topic, see "Coriolis was brilliant ... but he didn't have a high-speed camera - Part IV: maximum cue tip offset" (BD, October, 2005).
Sidespin (english) is used on the majority of shots to either control how the cueball comes off a cushion, or to reduce object ball throw (with outside english). In both cases, it is the amount of spin relative to the speed of the cueball that is important - the spin/speed ratio. This is governed nearly totally by tip offset, ie, how far from center tip contact is made. Cue speed and weight have a very slight effect. The heavier and faster the cue, the greater the spin/speed ratio (very slightly).
The factors that govern absolute spin rate, as with force follow and draw shots, have been mentioned (tip offset and cue speed), but just to add this. For any particular player, there is an optimal cue weight, one that produces the most spin, for each particular offset. No one cue will work equally well at all offsets for that player. But the good news is that over a rather broad range of cue weights, there is very little difference between them as far as cueball response. (The reason for this has to do with with the inertia of the player's arm.) Nevertheless, as a general rule, a heavier cue is more efficient at centerball, while a lighter one is more efficient away from centerball (in theory).
I would think that harder tips would be more efficient than softer ones, but some tests done by another poster here, Mike Page, suggest that this might not be the case, that they may be about the same. This is a part of cue efficiency as a whole. I suspect that there is very little difference between the "best' and "worst" cues as far as overall efficiency is concerned.
In brief, the principle factors (and virtually the only factors) are tip offset for spin/speed ratio, and tip offset plus cue speed for absolute spin rate. Having a well-chalked tip in good condition is important too, of course, as it determines how far from center you can hit.
For people who use "tips of english," tip shape can also affect the amount of spin they apply. See "Squirt - Part VI: tip shape" (BD, January, 2008) article for illustrations and explanations.
For people who want to see the math and physics behind many of Jal's statements above, see TP A.30.
outside english and gearing
Should I use outside english to reduce the effects of throw (i.e., "spin the ball in")?
If the exact amount of outside english (OE) (called "gearing" OE) is used for a given cut angle, the will be no throw. This can be useful in play when cling/skid/kick is a concern (e.g., under dirty and/or chalk-smudged ball conditions). Here's a good video demonstration of the effect:
and here are some others:
The "gearing" outside english handout and the following video, from Vol. I of How to Aim Pool Shots (HAPS), demonstrates how to use the 40% rule (see below) to aim shots with "gearing" outside english to eliminate cut-induced throw:
For more information, see "HAPS - Part III: Gearing Outside English," (BD, January, 2015). It can be difficult to have a feel for the exact amount of OE to use for different shots, even using the 40% rule; although, this feel can probably be developed fairly easily over time and experience. As long as one is just a little off with the amount of OE, the amount of throw can still be small enough to be a non-factor.
Diagram 2 in "Throw - Part VI: inside/outside english" (BD, January, 2007) shows how the amount of sidespin required for "gearing" OE varies with cut angle. Gearing OE is possible even with a 90° cut. And it is even possbile to throw the OB with spin-induced throw (SIT) at cut angles close to 90° (see impossible cut shots for examples).
Again, if the "gearing" amount of outside english is used, there will be absolutely no throw, and the OB will head exactly in the "line-of-centers" direction. Below is an illustration of an easy way to visualize how much tip offset is required to create a gearing amount of outside english (see TP A.26 for the derivation). The technique is called the 40% rule. Here's how it works: If you imagine or use your cue to visualize the line through the OB to the pocket, that gives the "line of centers." If you parallel-shift this to the CB (the red line in the diagram), that defines the "line-of-centers" point on the CB (the red dot in the diagram). The tip contact point must be a little less than half (2/5 or 40% to be precise) of the distance from center ball to the "line-of-centers" point to create "gearing" outside english.
With long, slow, follow shots, you must apply extra sidespin since some will be lost on the way to the OB. And on shots with significant drag action (where most or all of the backspin wears off on the way to the OB), less sidespin is required since the drag action increases the effect of the sidespin. For more info, see the drag shot effects resource page.
An alternative way to determine the gearing amount of outside english is to take 80% of 1 minus the ball-hit fraction. For example, for a 1/2 ball hit (0.5 or 50% ball-hit fraction), the gearing amount of english is 0.8 (1 - 0.5) = 0.4 [alternatively, 80% of (100% - 50%) = 40%]. This works for all ball-hit fractions. For more info, see TP A.26.
Using gearing outside english to eliminate throw as a variable is a good thing (when outside english is an acceptable choice), but the problem is that english also introduces squirt and swerve. Now, if the cue stick is as horizontal as possible (i.e., not elevated), and firm speed is used, swerve won't be much of a factor (but it can be in many pool shots). Concerning squirt, a low-squirt cue can help minimize the effect, and back-hand english (or front-hand english) techniques can be used to help compensate. However, for many shots, squirt and swerve effects might require significant compensation. Many factors and effects need to be considered when using english, per the list available here: english effects.
If cling is not much of a concern, and a player has a good feel for throw effects, maybe throw compensation (with aim adjustment) could be more straightforward than squirt/swerve/gearing OE compensation.
If cling is a concern (e.g., if the balls are old, worn, and very dirty with chalk smudges; or if you are pro, where cling on one shot can mean the difference in a match), OE might be appropriate for trying to eliminate throw and possible cling; but you need to be able to judge the required amount of english for all cut angles and be good at judging and compensating for squirt and swerve.
A problem with trying to eliminate throw with gearing OE is that the amount of throw is very sensitive to the exact amount of english when you are close to the "gearing" amount, especially with a stun shot. Therefore, the amount (and direction) of throw can vary quite a bit with small misjudgments and inaccurate application of the gearing amount of english. As demonstrated in HSV B.33, if you have more than the "gearing" amount, the the OB will throw in the direction of the spin (SIT: spin-induced throw); and if you have less than the "gearing" amount, the OB will throw in the cut direction (CIT: cut-induced throw). An argument can actually be made that using inside english is a better approach for dealing with throw. For information about how "gearing" english changes with cut angle, and for lots of illustrated examples, see "Throw - Part VI: inside/outside english" (BD, January, 2007) and "HAPS - Part III: Gearing Outside English," (BD, January, 2015).
Also, OE might not be appropriate for a given shot, based on position play requirements (e.g., to get position on the next shot, inside or no english might be required instead). So it seems one needs to able to compensate for throw anyway to be able to have a full arsenal of shots. Now, if you don't need english for position on a particular shot, this is a moot point.
Outside english can certainly be appropriate when trying to hold the cue ball (sometimes). For more info, see: holding the cue ball.
One thing is for sure: OE (or any english) is probably not the best choice with long-distance thin cuts, where aiming precision is key. Here, a center-ball hit will result in the best accuracy and consistency.
It's usually impossible to plan a run-out using only outside english, as has already been mentioned. You might have "english freedom" on 20% of your shots. If you're not going to hit a cushion or just barely bounce off a cushion, your side spin doesn't matter, so you are free to use what you will. If you have very good speed control and pattern planning, you might use the cushion on less than half your shots.
The main up-side in using outside english is that it eliminates throw and skid which come from ball-ball friction at the point of contact between the cue ball and object ball. With those eliminated, you are not at the mercy of changing frictional conditions on the shot.
The problem with using this "smooth rolling across the object ball's surface" technique is that it requires a lot of skill and experience to get right. The amount of outside required depends on the cut angle, the distance to the ball, and the amount of draw/follow. As has been pointed out by Dr. Dave, Ron Shepard and others, if you get it wrong by a little the shot can go wrong by a lot.
I think the main factor is on skids. This is also called "cling" and in snooker-playing regions "kick." I think the best name for it is "bad contact." In any case, it seems to be due to chalk at the contact point of cue ball on object ball and it causes large amounts of throw. Some players don't even realize that skid exists and think that when people complain about getting a skid/kick/cling/bad contact they are just trying to make excuses. Skids can happen on maybe 1 shot in 50 to 500 depending on conditions and the sort of shots taken.
So, where is this all going? If a player just flat out misses 30% of the shots he shoots at, he's got no reason to take special, complicated precautions to avoid a 1% problem. At that level he should be working on bringing his stick straight through the middle of the cue ball with maybe a little follow or draw. Nice and smooth and not too hard. Such a player has only a dim notion of squirt, swerve and throw, and probably no knowledge of skid.
On the other hand, if you're Rempe or Sigel or Hohmann, and on a good day you miss only one time in 200 shots attempted, you can't afford to have the object ball skidding off randomly one time in 100.
So the bottom line is that whether you should try to use outside english on the fraction of shots that allow the freedom to use it may well depend on how well you play.
from Patrick Johnson:
I believe the main difference between using inside and outside spin is familiarity. We naturally use outside spin more because (1) the places we want the CB to go are more often in the outside spin direction (because we're usually shooting into a corner) and (2) we can usually hit more softly with outside to move the CB the same distance (because the natural carom angle is usually in the outside spin direction).
This built-in preference for outside spin reinforces false feelings like the "helping english" and "self correcting" myths. In fact, since throw tends to correct for squirt but throw is reduced with outside spin, you have to adjust your aim more with outside than with inside, and a shot with "gearing" english is more sensitive to small spin errors.
What does it mean to aim sidespin shots with "parallel english?"
People use different definitions of "parallel english," but here is the standard and most common definition from the online glossary:
parallel english: aiming technique when using sidespin where the cue is placed parallel to the line of aim for a center-ball hit (with no sidespin) resulting in no compensation for CB deflection (e.g., for shots where swerve is expected to cancel the effects of squirt and throw, resulting in no net CB deflection, or where the amount of resulting pocket cheat is acceptable).
Some people instead interpret "parallel english" to mean: Based on experience, instinct, and/or intuition, place the cue in the desired stroking direction, with the tip already at the position needed to created the amount of sidespin desired, and with the cue already pointing in the direction necessary to compensate for squirt, swerve, and throw. In other words, don't line up center-ball first and then use a pivoting method (like BHE, FHE, or some combination) or a swooping stroke to arrive at the necessary line of aim to use the amount of sidespin desired. This is how pretty much all pros and great players aim when using english; although, this should not be called "parallel english" unless the cue is in fact parallel to the aiming line of the CB at address.
Regardless of how you determine the necessary stroking line of the cue when applying english, even if completely intuitively, the cue must be pointed in a certain direction for given shot to send the OB into the center of the pocket. For example, with a short distance between the CB and OB and/or with a firm shot, BHE (with an appropriate bridge length) will give you a good line of aim. If you use true parallel english with a shot like this instead, it will be way off (especially for larger amounts of sidespin). An alternative to BHE is to aim intuitively and bring the cue into the necessary line of aim with no pivot, but if you don't have the cue in the same direction created by the BHE approach, you won't pocket the shot (unless the pocket is close and/or large and can be cheated significantly).
spin axis "flip" demonstration
When you hit a striped ball with bottom-left english, and the stripe is initially aligned with the english direction, the stripe appears to "flip" during the shot. How does this work?
The following video demonstrates and explains (with the help of high-speed video) how the spin axis changes as drag converts bottom spin to forward roll, while sidespin persists. Here it is:
Check it out and give it a try. It's a cool visual demo.
"spin," "slide," and "roll"
What is the difference between "sliding" and "rolling", and can a ball "roll" when it has sidespin?
Good descriptions and demonstrations and "sliding" vs. "rolling" can be found here: normal roll, maximum offset, and overspin and cloth and cue ball effects. When a ball is sliding, drag action eventually converts bottom spin to stun and then to forward roll.
A ball starting out with pure sidespin and no top or bottom spin (i.e., stun) slides at first but immediately starts to develop forward roll due to sliding friction. See the spin axis "flip" demonstration for a good illustration of this. Once full roll develops, there is no longer any sliding. At that point, the ball continues to roll forward with sidespin. Both the forward speed and spin gradually slow due to rolling and spin resistance.
If a ball were rolling on an inked surface, the ink trace on the ball would be a circle. If the ball is rolling with no sidespin, the circle is vertical and goes around the full circumference ("great circle") of the ball. If the ball is rolling with sidespin, the circle is smaller and tilted. With more sidespin and/or less forward speed, the circle is smaller and more tilted. A ball with lots of spin and very little forward roll would trace a very small circle. A ball spinning in place traces a point (the smallest possible circle). Every "rolling" ball traces a circle, and as the sidespin wears off, the circle size and tilt angle change.
See OB "swerve" and "turn" for an explanation and demonstrations of how and why a ball rolling with sidespin travels in a straight line.
from Patrick Johnson (paraphrasing Mike Page):
Imagine that there's a cylinder (like a barrel) exactly the right size so that it's just contained within the ball. The cylinder/barrel's top and bottom edges meet the ball's surface like two latitude lines drawn around a globe in the northern and southern hemispheres.
Now imagine that you've tilted the barrel and are rolling it along the table's surface like you'd roll a barrel on its edge. You can see that the axis of rotation is tilted, and the barrel's bottom edge rolls along the table in a straight line without sliding at all.
Now imagine the ball surrounding the barrel rolling along with it across the table. This is how a ball rolls across the table with sidespin - no sliding, just rolling. If you were to put wet ink on the table it would mark a line around the ball at its "southern latitude" line.
The remaining wrinkle is that as the ball rolls its sidespin wears off and its axis of rotation becomes more and more horizontal. To visualize this, imagine that the tilted barrel within the ball tilts more and more onto its side, and simultaneously becomes fatter and fatter and shorter and shorter, but it continues rolling on its edge (you should be able to visualize doing this with a barrel that changes this way as you roll it). Eventually, when all the sidespin wears off, the fatter, shorter barrel becomes a flat disc rolling vertically on its edge. The wet ink line marked on the ball is actually a spiral that starts as a small tilted latitude and becomes a vertical "great circle" longitude when the ball is rolling normally without sidespin.
Can a cue ball have more top spin than actual rolling speed?
Yes, about 25% more. For illustrations and more information, see "Coriolis was brilliant ... but he didn't have a high-speed camera - Part IV: maximum cue tip offset" (BD, October, 2005). See normal roll, maximum offset, and overspin for more information.
There is often much confusion and misinterpretation about the various terms related to spin and english. Here's a good summary of definitions:
What is spin/speed ratio, and what effect does it have on a shot?
Spin/speed ratio (AKA spin-rate factor or SRF) is the amount of spin (side, top or bottom) the CB has in proportion to its forward speed. The spin/speed ratio is a measure of the intensity of the spin; and with sidespin, it is directly related to the amount of OB throw and rebound-angle change off a cushion. Immediately off the cue tip, the sidespin spin/speed ratio depends only on the horizontal tip offset from center. The vertical tip height (and resulting top or bottom spin) has no immediate effect on the sidespin spin/speed ratio. For a technical proof, notice that the analysis in TP A.12 - The relationship between cue ball spin and cue tip offset is not affected by tip height.
However, tip height does affect the amount of horizontal-axis spin (top/bottom), and that does affect the spin/speed ratio during the shot due to drag action. With more drag (as with draw shots), the spin/speed ratio increases as the CB approaches the OB or a cushion.
Also, when the CB hits an OB, its spin/speed ratio changes since the CB loses speed, but not significant spin, during the ball collision. This effect is greater with a smaller cut angle, where more of the CB speed is lost. So for a nearly straight follow shot where the CB heads nearly straight into a cushion, the spin/speed ratio and resulting rebound angle change off the cushion is much larger than with a shot with a bigger cut angle.
terminology and uses
What terms are used to describe different types of spin on the cue ball, and what is english used for?
English or "side" refers to sidespin applied to the cue ball (CB) by hitting left or right of the cue-ball vertical centerline. Proper usage suggests the term "english" is preferable to "English" for describing sidespin, but "English" is also commonly used. See VEPS II - English and Position Control for complete descriptions, illustrations, and demonstrations of all english-related concepts and terminology with shot examples.
Here are the different names used to refer to the type of english:
The purpose for sidespin is to alter the path the CB takes when it hits the rail cushions:
Here are some good resources and demonstrations to help you understand when and how sidespin is used:
For more examples and information, see:
Per the diagrams below, english (sidespin) is given different names (inside, outside, running, and reverse) based on how it is used.
Here are definitions from the online pool glossary:
inside english (IE): sidespin created by hitting the cue ball on the side towards the direction of the shot (i.e. on the “inside” of the cue ball). For example, when the cue ball strikes an object ball on the left side, creating a cut shot to the right, right sidespin would be called “inside english.”
outside english (OE): sidespin created by hitting the cue ball on the side away from the direction of the shot (i.e. on the “outside” of the cue ball). For example, when the cue ball strikes an object ball on the left side, creating a cut shot to the right, left sidespin would be called “outside english.”
reverse english (AKA "hold-up" or "check" english): sidespin where the cue ball slows and has a smaller rebound angle after hitting a rail (i.e., the opposite of “natural” or “running” english). The spin is in the direction opposite from the “rolling” direction along the rail during contact.
running english (AKA "natural english"): sidespin that causes the cue ball to speed up after bouncing off a rail, also resulting in a wider (longer) rebound angle. The spin is in the direction that results in “rolling” along the rail during contact.
For more information on specific topics, see:
How much tip offset is required to create perfectly natural running english, where the CB rolls on the cushion with no sliding motion?
from Patrick Johnson (from AZB post):
"tips of" and percentage english
What does it mean when somebody says "one tip of english" and how is "percentage english" defined?
"Squirt - Part VI: tip shape" (BD, January, 2008) and "Draw Shot Primer - Part VII: tips of english" (BD, July, 2006) illustrate and explain "tips" of english. "One tip" of english corresponds to shifting the cue one tip-width away from the center of the ball. Because the actual tip offset for "one tip" of english depends on both the tip size and shape, I prefer specifying the amount of english or sidespin as a percentage instead (100% for maximum english at the miscue limit, 50% at half of maximum, etc.).
When describing the amount of sidespin only, "percentage sidespin" is a measure of the horizontal distance between the tip-contact point and the vertical centerline of the CB, relative to the miscue limit on the horizontal centerline (equator) of the CB. Obviously, large percentages of sidespin are not possible at all tip heights on the CB (e.g., with follow and draw shots). The farther the tip is above or below the equator, the less the maximum possible sidespin will be. 100% sidespin is possible only on the horizontal centerline of the CB. "Percentage english" can also refer to other types of shots. For example 100% top-right english implies hitting the CB at the miscue limit in the 1:30pm direction, and 50% top-right corresponds to hitting at 1:30pm half way out to the miscue limit.
The illustration below, from the tip shape article, illustrates the difference between "tips of english" and "percentage english" (in this case, for pure sidespin):
Some people interpret "tips of english" to actually mean "1/2 tips of english." For them, "1 tip" corresponds to shifting the cue half of the tip's width (from the center of the tip to the edge). Using this scheme, the number of "tips" for the tip size and shape in the diagram above would actually be 0 for 0%, about 3/4 (2 * 0.37) for 25%, 1 1/2 (2 * 0.75) for 50%, and almost 3 (2 * 1.40) for 100%. Below is an illustration of the two common definitions of "tips:"
Here is a good illustration from Patrick Johnson (in AZB post) of how half "tips" can relate to thirds of maximum sidespin:
Some people interpret "tips of english" to actually mean "chalk marks." Here's a photo from an AZB post by iusedtoberich showing chalk marks (the round shape a chalked tip leaves on the CB after a hit):
Chalk mark (or "contact patch") size varies with tip hardness and shape, and with shot speed (see TP B.22), but the average size is about 5/32" or 4 mm. Maximum english is about 3 to 4 "chalk marks" or "contact patches."
A "tip of english" is also sometimes interpreted to mean "the amount of english that creates one diamond of angle change across the table" (i.e., one "diamond" of english); however, this will vary with the type of shot, the angle into the cushion, and table conditions. Here's a photo from an AZB post by Patrick Johnson illustrating this interpretation:
Obviously, it requires lots of feel and experience to know what tip position is required for each shot to create the amount of sidespin needed (e.g., to create the desired rebound angle change off a cushion). However, it is helpful to be able to communicate this amount to others in a clear and meaningful way. Clearly, based on the various common interpretations above, "tips" means too many radically-different things to too many people to be useful. A qualitative or percentage scale is much more meaningful. For example:
- a touch of english (0-10%)
- a small amount of english (10-30%)
- a medium amount of english (30-60%)
- a large amount of english (60-90%)
- near maximum english, close to the miscue limit (90-100%)
from Patrick Johnson (in AZB post):
The scale drawing below shows an overhead view of three cues hitting three cue balls at different offsets - cue moved 1/4", 1/2" and 3/4" to the left. Just for fun, it also compares where nickel and dime shaped tips contact the CB at those offsets, assuming the cue's centerline is offset the same amount.
I notice two interesting things:
1. These three very common tip offsets - often called 1, 2 & 3 (or 1/2, 1 and 1 1/2) "tips" - produce almost exactly 1/3, 2/3 and 3/3 of maximum sidespin (the red lines on the CB), which correspond to 1, 2 and 3 diamonds of cross-table angle change. I just find this correspondence remarkably convenient.
2. The difference in contact points for nickel and dime shaped tips (shown by the circles at the cues' tips and the lines connecting their centers with the CB's center) is almost nonexistent: 1/128" at 1/3 max sidespin, 1/64" at 2/3 max sidespin and less than 1/32" at maximum sidespin (true for nickel and dime tips of any width). So how true is it really that a dime shaped tip can produce noticeably more spin for the same tip offset?
from Patrick Johnson (via e-mail):
Center-of-Tip Spin Calibration
See the diagram below, where:
- Measure all side spin by where you point the center of your tip.
- Visualize the “center-of-tip” spin range from center ball to 2/3 the distance to the ball’s edge (vs. the “contact point” spin range of 1/2 the distance).
- Aim the center of the tip at the fraction of the larger spin range that corresponds to the fraction of maximum spin you want.
- the green hash marks are thirds of maximum side spin (where the stick's centerline is aimed)
- the red "x"s are fourths of maximum side spin (where the tip actually contacts the CB)
Because of the curvatures of the cue ball and the cue tip, the cue stick’s centerline must always be aimed a little farther from the cue ball’s center than the spot you want to hit.
To hit the CB precisely on the points that produce fourths of maximum side spin, aim your cue's centerline at the corresponding thirds of maximum.
AIM = HIT
1/3 = 1/4
2/3 = 1/2
3/3 = 3/4
4/3 = 4/4
This works because a typical tip's radius is (the curvature of a nickel or dime) is about 1/3 the radius of a cue ball, so the tip's center is always 1 1/3 x the contact point distance from center CB. Put another way, the contact point for any tip position is always 1/4 the distance from tip center to CB center. This geometric principle depends solely on the radius of the tip’s curvature, so it’s the same for all tip widths.
when to learn
When should someone start learning english (sidespin)?
I don't think a person should spend much time with english until his or her fundamentals and stroke are solid. When deciding to use english seriously, a person should also start learning about all of the effects that need to be taken into consideration. For more info, see aim compensation for squirt, swerve, and throw.
As far as the basic knowledge part, I think it is important to discuss that before the beginner starts using side spin. I point out how the side spin can be useful but at the same time I show five major problems with using it: squirt, swerve, throw, miscues and cling/skid/kick/bad contacts, and some of the details of those problems. Most beginners do not fully understand those problems when first introduced to them, but I want them to be aware that problems exist.
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