Dr. Dave's answers to frequently-asked questions (FAQs), mostly from the AZB discussion forum
Does the brand of chalk really make that much difference?
See chalk effects.
How long is the tip in contact with the cue ball?
Clips HSV A.77-A.81 and A.147-A.151 show close-ups of cue tip impact for various hardness tips and various speeds. Here are some conclusions:
For some super-super-slow motion videos and data for how contact time varies with cue speed, see DBKcue's page on this topic.
Some people think that what they do with their grip hand or follow through can change the tip contact time, but this is not the case (i.e., it is not possible to get a significant effect). Also, some people think a softer tip, which has a slightly longer contact time, can create more CB "reaction." This is not the case. The peak force isn't as large with a longer contact time (i.e., the force is spread out over a longer time). Therefore, the "hit" might "feel" slightly different to the player. However, the momentum effects (cue and ball speed changes) will still be the same, assuming the tips being compared have the same efficiency. Another thing that might be different is that a shorter contact time is usually associated with a harder tip, and a harder tip might have better efficiency, so the CB might have slightly more speed (with a given stroke) with a harder tip for a given cue mass and speed. And with more speed, less spin will be lost on the way to the OB or cushion, giving the impression that the hit created more spin.
With an increase in tip contact time, the effective tip offset will be slightly greater (because the tip will rotate out with the CB during contact), but this will also result in more squirt, which will diminish the effectiveness of the slightly larger tip offset. For more info, see cue tip hardness effects and getting more spin with an LD shaft.
For more info and resources on these topics, see:
tip hardness effects
cue tip efficiency
cue "hit," "feel" and "playability
effects of light vs. tight grip
How much does the tip deform during contact with the cue ball?
Here's an image from some high-speed video filmed by a group from Austria:
The full video clip can be viewed at HSV A.76 (it is the third clip in the sequence). The video was shot at 2000 frames per sec with a high-resolution color camera. Here's an isolated clip of the close-up of the tip contact:
I've collected a sequence of images from the video clip and have made them available in MS Word and PDF formats. The MS Word file is large (1.7 MB), but it is very useful. If you page down through the file to load all of the images, you can then use the scroll bar to simulate a flip-book animation. The faster you scroll, the faster the simulated "video" plays. The images are 1/2000 second (0.0005 or 5 ten-thousandths of a second) apart.
Here are some observations, insights, and questions from the collection of stills:
- The tip is probably relatively soft based on the contact time and amount of deformation. Contact lasts about 4 frames (over frames 3-6), which corresponds to about two thousandths (0.002) of a second.
- The cue tip seems to stay in contact with the ball as the ball starts to rotate, which might contribute to the amount of cue stick deflection.
- The cue tip had an excessive amount of chalk on it (as evidenced by the pre-impact chalk trail through the air and by the huge chalk cloud after impact).
Here's another excellent video showing the tip dynamics during contact:
See the following link for good examples of how the tip deforms and how the cue vibrates with both follow and draw shots.
What affects how well a tip delivers speed to the cue ball?
A hard tip will create more CB speed for a given cue speed. For more info, see:
From the experiment in the video, the range of coefficients of restitution (COR or e) were between 0.71 to 0.75 for playing cues with medium-hardness tips and 0.81 to 0.87 for jump and break cues with phenolic tips. The analysis at the bottom of TP A.30 shows the effect this has on break power. A phenolic tip can add about 17% more power or energy to a break as compared to a medium-hardness leather tip.
For other effects related to tip hardness, see cue tip hardness effects.
Cue construction (ferrule, joint, butt, and bumper) can also have an effect on both a cue's efficiency and hit/feel/feedback/playability.
A shaft that is very flexible (not very stiff), will tend to deform and vibrate more during a hit. This vibration represents lost energy because that energy remains in the cue and is not delivered to the CB. For more info and demonstrations, see the cue vibration resource page.
from Mike Page:
Given that the speed of sound in maple is 4100 m/s, I'm wondering if break cue manufacturers are barking up the wrong tree going to harder and harder tips.
Presumably the motivation for going to hard tips--phenolic or whatever--is a belief that they are more efficient in the way you describe above.
An unintended consequence, though, of these hard tips may be that because the contact time is shorter, there may not be enough time for the ball to "see" the full mass of the stick.
4100 meters/sec is 4 meters per millisecond. A round trip for the compression wave is about 3 meters (two stick lengths). So it takes about three quarters of a millisecond for the cueball to even have a chance of knowing about the back of the stick.
My guess is the contact time for break tips is in that range.
Why not try an efficient soft tip? Maybe get the contact time up to 1.2 ms or more?
The harder tips are more efficient (see HSV B.42 - tip and cue efficiency, with Bob Jewett).
My best measurements for phenolic tip contact time gave values close to 1/2 ms, but I didn't test at break speed. For more info, see: http://billiards.colostate.edu/threa...p.html#contact
Excellent points and questions. Anecdotally, it seems like the phenolic tips still provide an advantage over softer tips, which currently all seem to be less efficient.
How much force is generated between the tip and the cue ball during a break shot, and what would it take to generate a "ton" of force at the tip?
See: TP B.20 - Peak forces during a break shot.
As another example, and to keep things simple, let's use a cue weight of 18 oz and assume a perfect tip with a center-ball hit. For this case, TP A.30 predicts that the outgoing CB speed is about 3/2 (1.5) the incoming cue speed. Let's also assume that the average force during tip contact is about half the peak force. And let's assume the tip is in contact with the ball for 0.001 sec, which is typical.
For any CB speed (vb), given the CB mass (mb), the momentum delivered to the CB is:
mom = mb * vb
For a given duration of contact (dt), this momentum must equal the impulse delivered from the cue:
imp = 1/2 * Fmax * dt
So to find the peak force for a given CB speed:
Fmax = 2*mb*vb/dt
And for a given peak force, the CB speed is:
vb = Fmax*dt/2 / mb
And the cue stick speed required to create this is about:
vs = 2/3 vb = Fmax*dt / 3*mb
For a 20mph break, with a 6oz pool ball, the Fmax equation gives a peak force of:
Fmax = 683 pounds
To achieve a 1 ton (2000 pound) peak force, the vs equation gives a required cue speed of:
vs = 39mph
What differences does tip hardness make, and does it affect how much spin can be applied, or the amount of squirt that results?
Here are some relevant factors and effects related to tip hardness:
There is no question that a harder tip "feels" different and provides different "feedback" (a softer tip typically dampens the impact a little and the force of the hit isn't felt as strongly). It is also true that a harder tip can result in a more efficient hit, providing more speed to the CB for a given cue speed. And it is true that with slower CB speed, more backspin will wear off on the way to the OB with a draw shot and more sidespin will wear off on the way to the cushion with a sidespin shot (especially on slow and sticky cloth with slower shot speed). These effects might make it seem like a softer tip is applying less spin to the CB. Regardless, the quality of spin (i.e., the spin-speed ratio) delivered to the CB depends only on the tip contact-point offset from center. The physics on this is very clear. If anybody doubts this, they should do a careful and objective experiment to compare any tips they think would produce different results. For those who have math and physics backgrounds and are interested, the physics showing how the spin-to-speed ratio depends only on tip offset from center, even when accounting for tip efficiency, can be found in TP A.30 - The effects of cue tip offset, cue weight, and cue speed on cue ball speed and spin.
Some people think that because a soft tip stays in contact with the CB slightly longer (see contact time), a soft tip can apply more spin. However, see Bob Jewett's comments below. Also, the contact time is still extremely small with both a soft and hard tip: close to a thousandth of a second (0.001 s). Assuming the CB speed is the same in all comparisons, even though the peak force will be different (more with the shorter contact time), the amount of momentum (linear and angular) transferred to the CB will still be the same (because the sum of force over contact time is the same in both cases). The CB doesn't move much (translation or spin) during the extremely small contact time, so the only significant factor is the tip contact point at impact.
Now, it is possible that a hard tip, especially if it is not holding chalk very well, will have a miscue limit closer to the center than a soft tip that is holding chalk well. In this case, the soft tip will enable a player to apply more spin to the CB since the tip contact point can be farther from the CB's center without resulting in a miscue. Also, if one thinks a hard tip can't hit as far out on the ball (even if it can), one might tend to hit will less tip offset from center, which will result in less spin.
There are many factors related to tip hardness that could influence squirt, including: tip density/weight, tip efficiency, contact time, and effective endmass. "Return of the squirt robot" (BD, August, 2008) documents an experiment related to the effects of tip hardness on squirt. A softer tip did seem to create slightly more squirt, but the experiment was not very well controlled (see the article for more info). In general, if the contact time is longer (as is the case with a softer tip), the effective endmass and resulting squirt should be larger (see the rubber-super-ball-tip report as an example). Another set of more careful experiments documented in the Cue and Tip Testing for Cue Ball Deflection (Squirt) video and "Cue Tip Squirt Testing" (BD, June, 2014) seem to imply that tip type, hardness, and height have very little effect on shaft squirt. Among the wide range of tips tested in the video, the harder tips did result in slightly more squirt. This makes sense because the harder tips are denser and heavier, creating more "endmass." The shorter contact time seems to be less of a factor than the added weight.
Another factor involved with a softer tip is that it might better absorb glue and adhere to the ferrule more strongly and making it less likely to come off with lots of use and/or abuse.
from Mike Page (in AZB post):
I am well aware there is an entire lore surrounding this notion that a soft tip gets more action, gets higher spin-to-speed ratio -- and that you can find the claim from amongst the best players in the room, the best players in AZ Billiards, pro players, experienced players ...
I think this claim should enter the textbooks as a superb example of confirmation bias: http://skepdic.com/confirmbias.html
Aside from the subtle contact-time effect on the offset (a smaller effect than the claims), the claims are false.
The force that produces the speed and the force that produces the spin are the same force, and at a given offset any additional force increases the two in the same ratio. A soft tip acts slightly longer, but it's basically less force acting over a longer period, and the added-up result is the same.
There are shots designed to test the maximum spin-to-speed ratio, where you can get an actual top player trying to get maximum action using different tips--basically a slightly-off-angle draw shot where you are trying to hit a rail as far back as possible. I and others have done these empirical experiments, and the results have been consistent and agree with the expectations from the physical description.
from Mike Page:
Even if soft and hard tips held chalk exactly the same, it's possible the soft tip might reduce the chance of miscue. For instance, suppose a miscue occurs when less than 50% of the contact patch has chalk. If the bald regions are small, then this standard may be violated more frequently for a hard tip with its small contact patch.
from Bob Jewett:
One issue is which harness of tip will allow the farther-from-center hit. Some believe that a soft tip takes chalk better so it can hit the ball farther from center.
There is a counter theory, and that is because a softer tip will have a longer contact time than a hard tip. During contact, the tip rides around the side of the ball some, so the final eccentricity as the tip leaves the ball is larger than when the tip first hits the ball. A softer tip, with the longer contact time will be farther off center at the end than a harder tip with the same starting offset. If both tips can only hold to a certain point of offset, and you start your shot so the miscue point is barely reached at the end of contact, the average offset will be larger for the harder tip. This means that the harder tip can create more spin for a given ball speed.
Which dominates? Holding chalk better or starting farther off-center? I don't know of any experiment that has tested this.
How hard are some tip brands relative to others?
Here is a very thorough chart of tip types and hardnesses for a wide assortment of brands (from jschelin99 on AZB)
Here is a summary of some durometer hardness test results from FLYINGSNAIL on AZB.
SAMSARA JUMP - 86.0
BLACK DIAMOND - 81.0
SUPERPRO - 81.0
WB USA - 77.0
BLUE ELF - 76.0
LePRO - 74.5
TALISMAN - (M) 70.5
TAD - (M) 75.0
TRIANGLE - 73.5
"Blue milk duds" - 73.0-74.0
KAMUI - (H. BROWN) 73.5; (M. BROWN) 71.0; (S. BROWN) 62.5; (H. BLACK) 73.5; (M. BLACK) 72.5; (S. BLACK) 62.0
MORRI - (1ST GEN. WITH "S" ONLY) 62.0; (2ND GEN. SOFT) 71.0; (OLD MEDIUM) 77.0; (M III) 75.0
TRIUMPH - 70.0
BLACK KING - (S) 65.5 (M) 67.5 (H) 70.5
TIGER SNIPER - 67.0
BAMMA - 66.0
OLD ELK MASTER ORIGINAL - 65.0
and here's a buying guide (with some useful info) available from PoolDawg, including a large set of hardness data for most-commonly-used tips.
how to replace a cue tip
How do you replace the tip on a cue?
The following videos demonstrate the process and tools needs to replace a cue tip:
cue tip replacement (Seyberts)
replacing a cue tip (Home Billiards)
What are advantages and disadvantages of laminated tips?
Laminated tips are made by compressing and gluing together many layers of leather material, in an attempt to create more consistent properties as the tip wears down with use. Some people think laminated tips are better because of they don't seem to compress and harden with use, and they seem to provide more consistency over their lifetime; but others don't like them thinking they don't hold chalk as well or that the glue between the layers can affect performance. In the absence of hard comparison data, it just seems to simply be a matter of personal preference and psychology.
from arnaldo (in AZB post):
[quoting Jack Koehler:]
"Leather (from the donor animal) is not homogenous. The texture (and hardness) changes from the hair side to the inside. If the tip is made of one piece of leather, you get a simple progression from hard to soft. The thin pieces of leather skived for lamination purposes have these same characteristics but when you stack them, to get the proper thickness, the final product is much more homogeneous. The randomness of grain from layer to layer when compiling the stacks, which you properly mention, probably also plays a part in the resulting superiority and performance characteristics."
Is it important to remove the mushroomed edges of a tip?
If your tip is properly shaped tip and you are hitting the cueball within the non-miscue zone, the extreme edge of the tip doesn't come into play (e.g., see the diagrams in "Draw Shot Primer - Part VII: tips of english" - BD, July, 2006).
However, removing the mushroomed edges does:
For more info, see tip size and shape effects.
What brands of tip are commonly recommended?
Morri, Sniper, Triangle, and Kamui.
size and shape
Does the tip and shaft size and shape make a difference?
For applying english, a smaller-diameter and rounder tip (approximately "dime" radius) is generally recommended. Here are some possible reasons:
However, per the second quote from Patrick Johnson below, there really isn't much difference between a "dime" shape and a "nickel" shape.
One advantage of a flatter tip is that a center-ball hit, with some tip placement inaccuracy, will generally have less unintentional english (and unexpected squirt/swerve/throw). In other words, a larger, flatter tip is more "forgiving" with misalignment errors for near-center-ball hits. It may also be easier to control small amounts of sidespin since more cue offset is required to create more sidespin, as compared to a rounder tip. With stroking errors, where the cue is pivoted relative to the bridge, a flatter tip will result in less sidespin; however, the CB will head in the direction of the pivoted cue (minus the small amount of squirt corresponding to the small amount of sidespin). Therefore, the potential benefits of automatic stroking-error correction due to back-hand english (BHE) effects won't work as well with a flatter tip (unless the bridge length is very long).
Here's an expanded diagram from "Squirt - Part VI: tip shape" (BD, January, 2008) that illustrates tip shape effects:
Another concern related to shaft diameter is bridge comfort. With a closed bridge, some shaft sizes and tapers will be more comfortable than others to different individuals. This is less of a concern with an open bridge.
The shaft size and tip shape can also influence how some people apply english if they use "tips" of english and/or an aim-and-pivot squirt compensation system (e.g., BHE). This might make some people think they are getting more or less english with different size and shape tips. For more info, see "Squirt - Part VI: tip shape" (BD, January, 2008).
Tip shape can also affect the results of squirt-testing machines that position the shaft and CB the same with each test. If the tip shape is different from one shaft to the next, the effective tip offset will be different, creating a slightly different amount of squirt, with everything else being equal. This could have an adverse effect on squirt-testing results. In comparing shafts, identical tips should be used. Each shaft should be tested with the same tip size, shape, height, hardness, and weight.
Tip height can also have an effect on the amount of squirt (CB deflection) a shaft creates, especially if there is a heavy ferrule (e.g., brass) on the shaft. Pushing the heavy ferrule weight back from the CB (by using a taller tip, which is much less dense than the ferrule) even a little can make a significant difference on the shaft endmass and resulting squirt. Diagram 4 in "Squirt - Part VII: cue test machine results" (BD, February, 2008) documents experiments done to show the effects of mass at different distances from the CB.
from Patrick Johnson (from AZB post):
(The diagram above) shows four tips touching the cue ball at 30 degrees offset from center (about halfway from center to edge), which is about where the miscue limit is no matter what the size or shape of your tip.
There are two shaft diameters shown: top = 12.75mm; bottom = 10mm.
There are two tip shapes shown: left = nickel radius; right = dime radius.
As you can see, the larger diameter shaft (at top) contacts the cue ball farther from its edge at the miscue limit, and there's room at the edge of the tip to spare with either tip shape. This is because a 60-degree arc (30 degrees in each direction) on a nickel or dime radius is smaller than 12.75mm wide.
The smaller diameter shaft (at bottom) still has a small amount of room at the edge of the tip with the dime shape, but is right on the edge with the nickel shape. This is because a 60-degree arc (30 degrees in each direction) on a nickel radius is just about 10mm wide and on a dime radius it's just a little less than 10mm wide.
- Nickel or dime radius only makes a difference on very small diameter tips.
- On very small tips it's better to have a dime radius than a nickel radius.
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?
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