What makes a table bank short?
- Thread starter X Breaker
- Start date
Louis Ulrich
New member
Several factors could cause the rails to bank short but I think the most common is that the rails are too high. This would allow the ball hitting the rail to go underneath the cushion and get "spit out" faster than normal.
Other things might have to do with temperature of the room or humidity.
Other things might have to do with temperature of the room or humidity.
Stiffness of the rail makes a shorter table... really old rubber is a killer, I know this one table where the rails are as hard as a rock and sound like it too.
I've also heard that "commercial" rubber supposedly used in pool halls on heavy use tables is stiffer than normal billiard tables in order to last longer, but also plays shorter than it should...
I've also heard that "commercial" rubber supposedly used in pool halls on heavy use tables is stiffer than normal billiard tables in order to last longer, but also plays shorter than it should...
Good replies ...
previously, plus keep in mind that all rubber breaks down within 7 years of use. That's why there are a lot of 5-6 year old cars on the used car market, before all the rubber gaskets and hoses have to be replaced in them.
A lot of rooms will recloth reguarly, but overlook replacing rails unless there
is a glaring defect. They tend to think in the mindset that rails can always be fixed, instead of just replacing them.
previously, plus keep in mind that all rubber breaks down within 7 years of use. That's why there are a lot of 5-6 year old cars on the used car market, before all the rubber gaskets and hoses have to be replaced in them.
A lot of rooms will recloth reguarly, but overlook replacing rails unless there
is a glaring defect. They tend to think in the mindset that rails can always be fixed, instead of just replacing them.
nipponbilliards said:
Why does any ball bank short?
You'll hear all kinds of stuff about balls compressing deep into cushions and getting jammed under rails, but it turns out those explanations are unnecessary.
Both friction between the ball and the rail cloth as well as friction between the ball and the bed cloth play a roll in the observed bank angles and their speed dependence.
A bank is shortened because the object ball lacks running english when it hits the rail. That is, when there is not "natural running english," (the same idea as the amount of outside english that gets rid of throw on a cut shot), a ball striking a rail has in effect reverse (check) english. This reverse english is what shortens the bank. *
So why are banks shortened when hit hard but not when hit soft?
For a ball sliding into a cushion with no sidespin (the usual "drilled" bank shot) the angle is shortened because, as explained above, the absense of natural running sidespin is equivalent to a little reverse sidespin. *This shortened angle would be there for a soft shot too provided the object ball slid into the cushion (e.g., if the object ball is very close to the cushion). *This is as small as the angle is going to get. *
Beyond this the angle is widened by any topspin the object ball picks up on its way to the rail from friction with the cloth. *The topspin widens the angle because the spin is still there after the collision with the cushion--and from the point of view of the new off-the-cushion ball direction, this spin has a
sideways component (as though somebody just masse'd the ball). *
These effects together generate the observed speed dependence. *When you
shoot hard, the angle is shortened because the ball has picked up no
topspin yet has the reverse english. *As you hit the same bank shot softer
and softer, the reverse english effect is still there tending to want to
shorten the angle, but you are putting more and more topspin on the ball,
widening out the angle more and more.
Bob Jewett has a fascinating demonstration shot that will convince you it's not rail height or cushion depression that's shortening the banks. The idea is to get rid of the topspin effect even for soft shots. Freeze two balls aimed at an angle to the cushion with the closer ball a half inch from the cushion. That closer ball is going to be banked by driving the cueball into the frozen combination. Here the close ball has no chance to pick up topspin even at slow speeds. So it will always slide into the rail. The result is this ball banks to the same spot hit softly as it does at warp speed. This contrasts with the predictions of the jam-into-or-under cushion hypotheses and agrees with the predictions of the above explanations.
To respond to the original question, balls can seem to bank unusually short when the bed cloth is on the slick side and the rail cloth is on the sticky side. Perhaps they changed the bed cloth without doing the rails?
mike page
fargo
The main factors:
Dirty cloth.
Dirty Balls
Rail Height
Rail Rubber (wrong profile)
Most Pool tables play short from the factory. On a 3 rail bank the Cue
comes on average about 1/2 diamond short. This is with a good smooth
level stroke with natural running english.
The other factor for a ball coming short is of course the stroke itself. I see that most that play pool have a diving tip in there stroke. The tip always seeks the cloth. This will also cause a ball to come short snce many times this will cause the ball to draw off the rail.
Dirty cloth.
Dirty Balls
Rail Height
Rail Rubber (wrong profile)
Most Pool tables play short from the factory. On a 3 rail bank the Cue
comes on average about 1/2 diamond short. This is with a good smooth
level stroke with natural running english.
The other factor for a ball coming short is of course the stroke itself. I see that most that play pool have a diving tip in there stroke. The tip always seeks the cloth. This will also cause a ball to come short snce many times this will cause the ball to draw off the rail.
nipponbilliards said:
Hand-waving argument to follow:
For the most part, the cushions bank short because of cushion material, cloth, and nose profile. It's a return of energy vector physics thing. IMO, the nose profile affects the rebound more profoundly than the other two.
Speed only affects the bank in that it affects how much forward roll (or lack thereof) is on the ball when it hits the cushion. There are standard tests to prove this.
Almost every table with K66 profile cushions will bank short with no spin. The Diamond Smart Tables with their Artemis cushions and billiard profile banked pretty close to true at no spin at the SBE. Someone from the snooker world can tell me, but I recall that the flat faced cushions banked true with no spin as well.
Fred
I believe the most critical factor is rail cloth grip.
This can be affected by the thickness, cleanliness, newness of the cloth and also by the humidity (moisture content increases grip..though maybe pouring water over the rail may have the opposite effect).
This can be affected by the thickness, cleanliness, newness of the cloth and also by the humidity (moisture content increases grip..though maybe pouring water over the rail may have the opposite effect).
I agree with above on K66 rubber. But before you go to the expense of changing the rubber I would first look at the condition of the cloth and balls.Cornerman said:
If the cloth is worn out, (ready to change) take a damp towel and clean the cloth then get a can of Pledge furnature polish, hold it about 2 -3 feet above the table and spray it on the cloth as you quickly walk around the tabel (less than 10 seconds). The mist just drops down on the table. Some folks use silicone on a rag and wipe it on the table. There is a problem with doing this frequently. These products have oils that attract and hold dirt over time.
Then clean the balls. If you don't have access to a ball cleaning machine I'd recommend using "Polishing Compound" not "Rubbing Compound" Put the PCompound on a wet rag and clean the balls. This will take about 1.5 - 2 minutes per ball to get all the scuffs and burn marks out. Rinse them off and dry with a clean cloth.
Now try your bank or kick shot. Or Place the CB at about the edge of the corner pocket and hit Diamond 3 from the opposite long rail with natural running english. The cue should drop in the opposite corner pocket. Another test is to spot the ball and with 3 or 9 o'clock english hit (level stroke) the center diamond on the short rail. Your third diamond should come in opposite the first diamond from the corner. If it ends up further away from the corner the table is still short or the CB was not stroked properly.
If this doesn't help then it's time to look at rubber and you might as well change the cloth if it's been used a lot.
The next thing I'd look at is depending on the table design some rails can be shimed. If you can shim the nose down any, this will lengthen the table.
I believe for ever 1 degree angle you get about 1/2 diamond length.
I believe humidity and temperature are the biggest factors. My poolroom had a billiard table set up about fifteen feet from the big A/C unit in the transom of the front door, blowing right on the table. When I was playing someone that was beating me (it happened a lot) I would keep turning the A/C on and off every half hour or so. The angles would get so short you wouldn’t believe the shots you could make. Between the table being cold or warm or humid or dry, it drove players crazy. Johnnyt
Last edited:
I don't know about fascinating. Lots of players get upset when you point out the fact that it's not really speed itself that causes shortness of bank. But for more on this, including measurements of three kinds of tables, seemikepage said:
http://www.sfbilliards.com/articles/2004-08.pdf
(One correction to the article: the subtitle is incorrect. It was egg on some other columnist's face that was apparent. I forget right now who had repeated the "harder = shorter" myth.)
An interesting result: snooker cushions bank longer for harder shots.
As for rails dying in 6 years, that's a bunch of hooey in my opinion. I have a table at home that plays fine with cushions that must be 30 years old now, and I regularly play 3-cushion on a table with cushions that are probalby that old as well. Good cushions should last for decades. Recently one major company sold a lot of bad rubber that died within 5-10 years. That should not be accepted as a standard. The symptom was that the rail rubber turned into something like pottery.
Great explantion. If I read you right, I think you're saying that friction alone accounts for the shortening, or very nearly so. In other words, you don't have to bring in compression effects in the rubber to explain it. Based on some simple math, I also think this is true but am wondering how certain this is?
It's interesting that you brought up the throw analogy. For certain types of shots (a fair amount of them in fact), the amount of throw is independent of the amount of friction between the balls (the coefficient of friction), unless there is a major drop in it. That is, unless the coefficient is zero, there are always some shots for which this is true and the range is greater the larger the coefficient. For instance, with soft to moderately hit stun shots, it applies to cut shots up to around 30 degrees (half ball hit).
The same applies to bank shots when the object ball is essentially stunned into the cushion. If it doesn't pick up much in the way of follow, it should come off the cushion at nearly the same angle regardless of how much friction is present, unless there is a rather large drop in it. A qualification is that friction effects with the bed are an exception - they do depend on the coefficient. But they are small compared to the cushion effects and therefore variations don't alter the results that much.
For a normal amount of friction (u=.2), I figured this is true for incoming angles up to around 55 degrees with respect to the perpendicular (but don't quote me). If the coefficient is less, then the range of angles for which this is true would be less, but would still cover most banking angles unless the drop in the friction was very great.
I think this is why bank pool playeres tend to hit their shots pretty briskly. They get more consistent results from table to table and under varying environmental conditions, at least as far as the friction is concerned.
Jim
Although you didn''t say this, it might be infered that natural running english will yield angle out = angle in. This isn't so because some of the ball's speed perpendicular to the cushion is also removed (around 20% - 30%) depending on the incoming angle. Therefore, to achieve equal angles it has to be slowed down in the parallel direction too. In fact, the spin has to be considerably less than natural running or "roll-off" english for this to occur.mikepage said:
It's interesting that you brought up the throw analogy. For certain types of shots (a fair amount of them in fact), the amount of throw is independent of the amount of friction between the balls (the coefficient of friction), unless there is a major drop in it. That is, unless the coefficient is zero, there are always some shots for which this is true and the range is greater the larger the coefficient. For instance, with soft to moderately hit stun shots, it applies to cut shots up to around 30 degrees (half ball hit).
The same applies to bank shots when the object ball is essentially stunned into the cushion. If it doesn't pick up much in the way of follow, it should come off the cushion at nearly the same angle regardless of how much friction is present, unless there is a rather large drop in it. A qualification is that friction effects with the bed are an exception - they do depend on the coefficient. But they are small compared to the cushion effects and therefore variations don't alter the results that much.
For a normal amount of friction (u=.2), I figured this is true for incoming angles up to around 55 degrees with respect to the perpendicular (but don't quote me). If the coefficient is less, then the range of angles for which this is true would be less, but would still cover most banking angles unless the drop in the friction was very great.
I think this is why bank pool playeres tend to hit their shots pretty briskly. They get more consistent results from table to table and under varying environmental conditions, at least as far as the friction is concerned.
Jim
Louis Ulrich said:
I agree Louis- Nothing aggravates me more than hitting a shot the correct speed, only to see the cue ball pick up speed off the rail because it's too high. Worse case scenario, the ball hops in the air after contact. However, I don't know if it's the most common. At least not around here. I think with the changing humidity/climate, a table that plays one way can also feel foreign in an hour with a brisk breeze blowing in from an open door.
typically a rail not banking correctly comes from the set up of the table. Proper rail height is key; most other factors such as moisture, how dirty the cloth and balls are play different factors on a bank based on the speed each shot is hitJosh Palmer said:
Josh Palmer said:
Just to clarify something here. I don't believe a ball can ever "accellerate" off of a rail. It's just not losing as much energy on rebound as you'd expect it too. If the ball actually left the rail at a higher rate of speed, then I believe you would've discovered "flubber" or rather a new energy source.. They'd setup power plants with rails set barely a balls width apart and drop a ball in and collect free "energy."
As well Some of the laws of physics (from what little I know) would be shot all to hell in a handbasket.. LOL
DJ
The snooker rail has a flat edge, and a steel block behind the cushions (on some high end tables), the cloth has a nap. I feel that the angles are different on the snooker tables. Some believe the amgels are more "true," I am not sure as I have never studied them.
Last edited:
PlynSets said:Just to clarify something here. I don't believe a ball can ever "accellerate" off of a rail. It's just not losing as much energy on rebound as you'd expect it too. If the ball actually left the rail at a higher rate of speed, then I believe you would've discovered "flubber" or rather a new energy source.. They'd setup power plants with rails set barely a balls width apart and drop a ball in and collect free "energy."
As well Some of the laws of physics (from what little I know) would be shot all to hell in a handbasket.. LOL
DJ
The sidespin, english, can be transfered to the cushion (energy) and make the ball increase its speed. The tradeoff is the energy(sidespin) that it uses to accelerate. Without spin, of any kind you are right, however the kinetic energy of the spinning ball can make it move faster. The draw shot is a perfect example. Straight on, all forward momentum (energy) transferred to the OB, the CB starts moving back. Where does energy come from? The spin on the ball. Now if the energy companies could just spin their................
On some tables, the rails are so hard. If I hit the ball hard, it narrows the angle; if I hit it soft, it would not move much.
So, I need to try hit the ball softer with lots of spin to make the angle wider, but the spin dies after the second rails; if I try to hit the ball hard, the spin will not take.
I always do very poorly in one local tournament because the pockets there are quite tight, and the rails are quite slow. The tables are about one diamond short. I really cannot get used to it.
It is a nice pool hall and I really enjoy going there. I wish I knew how to overcome this problem.
Thank you.
Richard
So, I need to try hit the ball softer with lots of spin to make the angle wider, but the spin dies after the second rails; if I try to hit the ball hard, the spin will not take.
I always do very poorly in one local tournament because the pockets there are quite tight, and the rails are quite slow. The tables are about one diamond short. I really cannot get used to it.
It is a nice pool hall and I really enjoy going there. I wish I knew how to overcome this problem.
Thank you.
Richard
Sure you can
Sure it can. It converts spin (rotating vector) into motion. Try hitting a soft two rail shallow angled (30 Deg or less) shot into a corner. The cue ball recieves rotational component from first rail and turns it into motion (speed increase) on second rail (plus angular distortion). Throw in a little inside english and you get more. 'm ignoring losses etc.
Nick
Sure it can. It converts spin (rotating vector) into motion. Try hitting a soft two rail shallow angled (30 Deg or less) shot into a corner. The cue ball recieves rotational component from first rail and turns it into motion (speed increase) on second rail (plus angular distortion). Throw in a little inside english and you get more. 'm ignoring losses etc.
Nick
PlynSets said:Just to clarify something here. I don't believe a ball can ever "accellerate" off of a rail. It's just not losing as much energy on rebound as you'd expect it too. If the ball actually left the rail at a higher rate of speed, then I believe you would've discovered "flubber" or rather a new energy source.. They'd setup power plants with rails set barely a balls width apart and drop a ball in and collect free "energy."
As well Some of the laws of physics (from what little I know) would be shot all to hell in a handbasket.. LOL
DJ