Dr. Dave's answers to frequently-asked questions (FAQs), mostly from the AZB discussion forum
What affect does the condition of a cloth have on play?
Two physical properties describe the condition of a cloth: sliding friction ("slick" vs. "sticky") and rolling resistance ("slow vs. "fast"). A "slick" cloth has very little sliding friction and allows the CB to retain its spin longer. For example, it is much easier to draw the ball on a "slick" cloth. A "fast" cloth offer very little resistance to rolling, so the balls roll much farther before coming to rest.
Cloth friction has an important effect on draw and follow shots at an angle. With a slick cloth, the CB persists along the tangent line longer before curving to the final direction, as demonstrated with speed changes in this video (a faster shot simulates slicker conditions):
In general, a new and clean cloth in a dry climate is usually more "slick" and "faster" than old and dirty cloth in a humid climate. A dirty cloth can also lead to dirtier balls, which can result in more cling. For more info, see the cling resource page.
For more information on how the drag effect of cloth friction affects various types of shots, see:
Cloth friction also has an important effect on CB swerve and massé shots. A slick cloth delays the curve, causing larger net cue ball deflection (the combined effects of squirt and swerve) for sidespin shots, and causing the CB to swing out more with massé shots.
For more info on the effects of humidity, see: humidity effects.
Also see the ball surface treatment resource page, because reducing CB friction has the same effects as a slick cloth.
What is pool table cloth made of, and what are the different brands and types?
Here's a good cloth buying guide which explains various options: https://poolfelt.com/pages/choose-pool-table-felt-style
How does the cushion deform during a high-speed kick or bank?
Here's a good slo-mo video of this: HSV 6.1 - Cushion deformation during a high-speed kick or bank. And here's another:
And here are some actual shots that take advantage of this effect:
And here are some others from from Vol. V of the Video Encyclopedia of Nine-ball and Ten-ball (VENT):
For more information, see VENT – Part IX: Rail Cut Shot Effects (BD, June, 2018) and VENT – Part X: Herd and Compress (BD, July, 2018).
Here's a bank shot (made famous by Eddie Taylor) that uses cushion compression and pocket facing stiffness to avoid a double kiss:
cushion nose height
Why is the height of the rail cushion nose not at the center of the ball?
Here is the rail cushion nose height specification, as dictated by the WPA:
"Rail height (nose-line to table-bed) should be 63 ½% (+1 %) or between 62 ½% and 64 ½ % of the diameter of the ball."
If the cushion nose height were at the ball center (0.5D), instead, rebounding balls would slide more and would hop significantly if they come into the cushion with topspin (especially at fast speed).
Another obvious height would be at the "center of percussion" of the ball (0.7D), per TP 4.2, so the rebounding balls would tend to roll away from the rails more naturally. However, this height would tend to drive a rebounding ball down into the table, which would tend to slow the ball more, accelerate cloth wear (and faster formation of a "rail groove"), and cause the rebounding ball to hop.
The WPA 0.635D offers a good compromise between the 0.5D and 0.7D values. This height was determined empirically to result in good rebound performance without too much ball hop or cloth wear.
drawing lines on the cloth
How can I draw lines on the cloth for lining up practice shots or for marking the rack location?
I put lines on my table for practice by using a construction chalk line. You pull the line out of the spool, pull the line tight between the two points, then snap it. Then I vacuum up the excess dust. For example I place a line diagonal from corner pocket to corner pocket. Then can practice progressive straight in shots and align the balls exactly straight on the line.
Also I use "tailor's chalk" which you can get at a fabric store or a sewing store. They use this to mark hems on pants legs for how high they should be. It is white and triangular shaped with sharp edges. I use this to mark where the rack goes on the table for quicker racking - commonly done with 14.1 (straight pool). Again this leaves "particles" on the table after marking, so I vacuum after marking the table.
from Deeman (concerning the head string line):
They use a pen with white ink. You can get one at a crafts store. The white pen does seem to be the best choice for permanent lines although i have the standard black ones.
Where can I find information on pool equipment specifications like cushion height?
Here is a link to the official specifications published by the WPA: equipment specifications.
how to clean and maintain
What's the safest and most effective way to clean a table's cloth?
from Fran Crimi:
Two things you don't want to see happen to your cloth regardless of it's type, are stretching and breaking too many fibers which result in fuzziness.
Vacuums with a hard pull will stretch the cloth. Rotating brushes will obviously break more fibers than non-rotating brushes. If I were you, I'd get rid of the rotating brushes and use a fine brush on a vacuum with a light pull. Then move the vacuum in one direction down table...and this has nothing to do with the cloth being directional or non-directional. This is about breaking the least amount of fibers as possible. Don't go back and forth like you're vacuuming your carpet.
When you're done with that, run a slightly damp cloth in one direction down the length of the table, always towards the foot rail, and let it air dry. No blow dryers. Vacuum as infrequently as you can. The more often you do it, the more fibers you'll break. Simonis 860 should not be even slightly fuzzy, unless you're breaking the fibers.
What should I do to keep my table in good condition?
1. Keep the table clean - cover it when not in use; don't let food or drink near it; keep junk off the rails. Let everyone know that the table is to be treated with respect and care, then be sure and follow your own advice.
2. Avoid using talc. Also, do not chalk your cue over the table, or place the chalk upside-down [open-side down?] on the rails.
3. Brush your table regularly (after each session is not too often), and clean the rails with a damp cloth.
4. Vacuum the table at least every few weeks with a dust buster type. Avoid using a vacuum cleaner with rotating brushes unless you have worsted wool cloth, like Simonis or Granito. Also, if you have a non-worsted or directional cloth, always brush or vacuum the cloth in the same direction, usually head to foot. Vacuum the table brush itself to remove the chalk dust.
5. At least once a month, use a damp lint free towel to wipe down the cloth. Some prefer instead to mist the cloth with a water and then brush it.
6. Wash the balls regularly, at least with water, or maybe mild soap and water.
7. If you want to practice jump or massé shots, get a little extra square of cloth to put under the cueball, or you may leave little white marks all over the table.
8. Don't let people sit on the rails - it will cause the cushions to come loose.
How does an increase in humidity affect how a table plays?
With more humid conditions, the following changes occur:
Are there standards for the sizes of the pockets on different tables?
There are standard sizes (and other geometric specs), and they can be found on the WPA equipment specifications page. An illustration of the different parameters can be found in TP 3.5. However, not all tables are made the same. Rails and pockets can vary significantly from one manufacturer to the next. The side pockets are usually larger than the corner pockets, especially on larger tables; however, on many coin operated "bar boxes," the opposite is often true. Pockets are also sometimes "shimmed" to make the openings smaller to make the table play "tougher."
For more information about pockets, see:
"speed" of the cloth
What is the "speed" of the cloth, and how do you measure it?
Here's a good article from Joe Waldron on this topic, showing how to fabricate your own device to measure and compare cloth "speed."
Related information concerning the effects of cloth "speed" on draw and drag shots can be found here.
For more information on the effects of various cloth conditions, see cloth effects.
from Bob Jewett (in AZB post):
It is also possible to measure the speed of a table with a stop watch. If you time a lag shot from far rail to stopping just before the near rail, the time in seconds squared times 2 gives you the reciprocal of the effective slope. So, 7 seconds for a lag to travel the length of the table gives:
7*7*2 = 98
slope = 1/98 = 1.0% more or less
On a carom table, it is not uncommon for a lag to take 10 seconds for the last lap of the lag:
10*10*1.8 = 180 (1.8 factor for a 10-foot table)
slope = 1/180 = 0.55%
Since most people can do lags and have stop watches or stop watch apps, this is a pretty simple and accurate way to measure table speed.
Also, if a video has a lag, you can pick the speed of the table off the time of the video.
standard pool table dimensions and required room sizes
What are the standard pool table sizes and dimensions, and how large of a room is required for each?
Standard size pool tables, along with the playing surface dimensions (measured between the noses of the cushions) are:
12-ft (snooker): 140" (356.9 cm) x 70" (177.8 cm)
10-ft (over sized): 112" (284.5 cm) x 56" (142.2 cm)
9-ft (regulation size table): 100" (254 cm) x 50" (127 cm)
8-ft+ (pro 8): 92" (233.7 cm) x 46" (116.8 cm)
8-ft (typical home table): 88" (223.5 cm) x 44" (111.8 cm)
7-ft+ (large "bar box"): 78-82" (198.1-208.3 cm) x 39-41" (99.1-104.1 cm)
7-ft ("bar box"): 74-78" (188-198.1 cm) x 37-39" (94-99.1 cm)
6-ft ("small bar box"): 70-74" (177.8-188 cm) x 35-37" (88.9-94 cm)
More info can be found here: Wikipedia pool table dimensions resource page.
The minimum space for a table is the playing area plus the length of a cue (58") plus about 6 inches for the back swing, more for comfort, on each side. This gives:
44" x 88"
14'4" x 18'
4.37m x 5.49m
46" x 92"
14'6" x 18'4"
4.42m x 5.59m
50" x 100"
4.52m x 5.79m
70" x 140.5"
16'6" x 22'5"
5.03m x 6.83m
"Seven foot" tables vary in size. Work down from the 8' dimensions. "8+" is an "oversized" 8-foot table.
If your room does not meet these minimum size requirements, many billiard retailers will suggest that you can still put a table in, and use short cues (52", or 48"). Many people have found they are unhappy having to resort to shorter cues, and should have either gotten a smaller table, or no table at all. Others, of course, take the opposite view -- they are delighted to have any table.
In the end, only you will know whether you are happy with the room dimensions and need for short cues. Before you spend $2000 for a table that will cause you to smash the walls in frustration, try this:
(1) Find an indulgent pool hall when it's not busy.
(2) Measure your space (at home) carefully, including the distance from the table to all walls that require a special cue
(3) Go to the pool hall with a piece or pieces of plywood or some such, and a short cue, and set up the "walls" to replicate where the walls would be in your house. Play for several hours, using the short cue when needed.
Between two tables you can do with about the length of a cue, the limit is caused not by the cue, but by the player being able to go into his stance between the tables. Deluxe rooms really need more room on all sides to let possible passers-by move without bumping into the players.
from realkingcobra (on AZB):
A 4 1/2 x 9ft pool table gets it's measurements from finish of rail to finish of rail.
4 1/2 feet = 54"
9ft = 108"
Take the playing surface of a 9ft pool table, it's 50"x100" now add in the 2" of cloth on the cushions on the side rails to the playing surface, what you come up with is 2" of cushion/cloth on the left side rail, plus 2" of cloth/cushion on the right side rail, plus the 50" of the playing surface from side to side. Now, add that together and you have 2"+2"+50" = 54" which equals 4 1/2 feet.
Now, if you double that measurement you'd be adding up 4 side rails at 2" each...remember you're DOUBLING the width, so that means instead of adding just 2 rails, you'd be adding up the width of 4 rails, at 2" each, plus you'd be doubling the width of the table side to side being 50" twice, so thats 100"...now add up....2"+2"+2"+2"+50"+50"= 108" which equals 9 feet even, EXCEPT....we all know all pool tables only have 2 end rails and NOT 4, so in order to keep the playing surface twice as long as it is wide...you have to subtract 2 of them 4 rails as ghost rails....meaning they're not really there on the pool table, so if you take and subtract the 4" of ghost rails from the 9ft...108" that leaves you with 104", now subtract the 4" of cloth/cushions that ARE on the table, and you end up with 100"....so that's how you get a 50"x100" playing surface out of a 4 1/2 x 9 pool table.
table difficulty factor (TDF)
Is there a way to measure and quatify how difficult a table plays?
The Table Difficulty Factor (TDF) system provides a very easy system to measure how "tough" a table plays. It is based on table size and the three corner-pocket measurements illustrated below. Four factors are used to account for table size, pocket size, pocket wall angle, and pocket shelf depth. Each factor is a number less than, equal to, or greater than 1, where 1 indicates average or standard. By multiplying the four factors, you get the TDF which is a good measure of table "toughness." If TDF=1, the table has an average level of difficulty; if TDF>1, the table plays more difficult than average; and if TDF<1, the table plays easier than average.
See the Table Difficulty Factor (TDF) document to see how values for the following four factors are assigned:
TSF: table size factor
PSF: pocket size factor
PAF: pocket angle factor
PLF: pocket shelf factor
The total Table Difficulty Factor (TDF) is calculated by multiplying the four factors:
TDF = TSF x PSF x PAF x PLF
The TDF can also be calculated automatically from table and pocket measurements using the Excel TDF calculator spreadsheet or the mobile-friendly online tool provided by "Isaac" on AZB. Example TDF ratings for a wide range of table sizes, types, and brands can be found in the AZB TDF thread.
The TDF can be used to adjust numbers from any scoring or rating system like the Billiard University Exams, "playing the ghost" drills, Hopkins Q Skills drill, or the Fargo rating drill or handicapping system. An effective score, taking table difficulty into consideration, can be calculated with:
(effective score) = (raw score) x TDF
See the TDF document for details and examples. And for more information, see: "Billiard University (BU) - Part IV: Table Difficulty" (BD, November, 2013).
All of the values and ranges for the individual TDF factors (TSF, PSF, PAF, PLF) were chosen very carefully based on how each factor affects the margin of error for a wide range of shots. In particular, the analyses and data in TP 3.4 - Margin of error based on distance and cut angle, TP 3.6 - Effective target sizes for slow shots into a corner pocket at different angles, and pocket "size" and "center" resource page were good starting points. However, adjustments were made based on anecdotal and empirical evidence for how tough a wide range of tables actual play. Many people provided input to guide these changes. Quite a few AZB users provided valuable input and feedback on the AZB TDF thread; and Mark Finkelstein, Mike Page, and Bob Jewett were particularly helpful in sharing their experience and judgement. Some of the factors that helped guide the adjustments include:
For more rationale and justification, see "Billiard University (BU) - Part IV: Table Difficulty" (BD, November, 2013).
How does side pocket size affect a table's difficulty level?
When the TDF system was developed, side pocket measurements were excluded to keep the system as simple as possible (requiring as few measurements as possible) while still capturing the most important characteristics of a table. On most tables, it is the corner pocket toughness (and not the side pocket toughness) that dominates overall table difficulty level.
For a comparison of the effects of side pocket and corner pocket difficulty effects, see the effective pocket size resource page.
How was the "standard" table measurements decided?
The measurements are mostly based on the centers of the WPA table specification ranges. But changes were made based on recent trends and input from table mechanics. Regardless, the chosen values aren't really that important, and what is considered "standard" has changed over the years (and will probably continue to change). What is important is the relative comparison between tables, which the TDF system provides. The rationale used to create the number ranges and values in the TDF tables (which control relative comparisons) is summarized above.
from realkingcobra in AZB post:
Facings play a major role in rejecting balls from pockets as do cushions. Take the Olhausen tables for example. The cushions are very...very soft, the facings are 1/8" and very soft. What happens on an Olhausen table is that when you're attempting to pocket a ball in the corner pocket coming down the rails, you're shooting the ball right into the outer have of the pocket facing with no rail wood support behind the cushion. When you do this, what happens is that when the ball being pocketed hits the facing, instead of deflecting to-wards the back of the pocket, it compresses the facing and cushion kind of like creating a flat spot at the end of the cushion, which in turn kicks the ball across the pocket to the opposite facing and back out again, and you don't even have to shoot the shot hard to get this "rejection" to happen. So, now comes in the role of the facings. If the soft 1/8" facings are replaced with harder 3/16" neoprene facings, these facings don't compress nearly as much when you shoot a ball into them, so the balls that would normally reject....go in because they deflect off the facings deeper into the back of the pocket.
from Sloppy Pockets in AZB post, concerning how to properly measure the pocket mouth and throat dimensions (at the intersections of the yellow lines, not at the labeled red dimensions):
from iusedtoberich AZB post:
Perhaps something like laying post it notes stuck on the cushion can extend the lines of the cushion to a real intersection point, that can then be measured to and from.
What are all of the terms used to describe different features on a pool table?
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