Bob Jewett Wrong Size, Wrong Shape You should probably have that looked at.

Recently on the Internet discussion group It depends. The difference in size has a cor- feet, just from being that small amount rec.sport.billiard, Pat Johnson of responding difference in weight, and that lighter. mentioned a problem he had with his new will make the cue ball rebound off the object Now suppose the poolhall buys new object cue ball. When he put the cue ball on the ball differently. If you have only a vague balls, but keeps the old cue ball. That would table and surrounded it with six used object idea of where the cue ball is supposed to go roughly double the relative differences in balls from the poolhall, he couldn't get all on any particular shot, the difference will not diameters and weights, and for the example the balls to freeze. There would be gaps be noticed, but the better your position play draw shot I just described, the cue ball between the object balls, and if he moved the becomes, the more such discrepancies will would come back twice as far (four feet) as balls around so there was only one gap, it bother you. a standard cue ball against a standard object was 3/32nd of an inch, as shown in ball. If you instead try to follow with the Diagram 1. This seemed to show that the light cue ball, you will be similarly surprised balls were smaller than the cue ball. when the ball goes forward only 64 percent Pat's question was: How much smaller are as far as you were expecting. So three dia- the object balls? monds-length of attempted follow ends up a I made a quick guess that if you divided The better your position whole diamond short. the gap by 6, the diameters of the object How do these measurements compare to balls would be smaller than the cue ball by play becomes, the more the equipment specifications in the Billiard that amount, or l/64th of an inch. It turns out Congress of America rule book? Balls are that I was off by a factor of two. Two other supposed to be 2.25 inches in diameter with- participants in the newsgroup, Jim (who the discrepancies will in a tolerance of +/-0.005 inches. (Typical goes by the user name "JAL") from Indiana high-quality new balls are much more exact and David Hood from Colorado correctly bother you. than that.) Assuming that the middle ball in pointed out that the ratio is about 3, so Pat's the cluster is the correct size, this means that cue ball was a whole l/32nd of an inch larg- the gap when you attempt to freeze six balls er than the object balls he was trying to play around it can be no more than 0.015 inches, with. which is about 1/64 of an inch, or the thick- By a coincidence, just after this online dis- Let's take an example of a draw shot with ness of a business card. cussion, one of the players in the 14.1 league the small cue ball. If a normal ball is 6 So far, we've been assuming that the object I play in brought his new cue ball to use in ounces, the small cue ball is only 5.67 balls are all the same size. If a ball has to be his match. I showed the two players how ounces. (This is calculated from the cube of replaced, this will not be true. The object much of a gap the cue ball caused between the ratio of the two diameters, if you want to balls we measured above were about 1/24 the surrounding balls, and it looked to be 1/8 try a different case yourself.) Suppose you inch smaller than a new ball. Suppose the 9 of an inch. We ball has to be then tried putting replaced in that the house cue ball set. There's no in the middle of way that you will the cluster, and we ever get a tight got a different with the new type of gap. It was 9 ball in the center between the because the old, frozen object balls small object balls and the cue ball, just can't stretch and it was nearly around it. as large as the gap Unfortunately, illustrated in even a l/64th- Diagram 2. inch gap — which Amazingly you might see enough, according with new, in-spec to Jim's and David's analyses, you can find are making a shot where, if you start the cue balls — is large enough to make a difference the difference between the cue ball's and ball with near-maximum draw, it might in how a rack breaks. object balls' diameters again by dividing the arrive with about half of that after rubbing Many years ago, before I had my first run gap by 3, even though the gap is made in a on the cloth on the way to the object ball, of 50 at , I played day and night very different way. For this example, the and you would get two feet of draw. On the in a rec room with old, worn balls. I thought house cue ball was smaller by 1 /24 of an inch. same shot, the smaller cue ball will get about I was pretty good because I could draw the Is 1/24 of an inch enough to worry about? 43 percent more draw and come back three cue ball all over the table. What I didn't real-

32 BD-DECEMBER 2005 ize, even though it was in front of me on mon, and shots were often made or missed across in all directions — they are all the every shot, was that the cue ball was tiny by the little hook the ball took at the end of same, but the shape is clearly not a circle. compared to the object balls, relatively a low-speed shot. When a billiard ball got Similar weirdnesses can happen in three speaking. With draw coming so easily and too oval, it had to be turned down with a spe- dimensions. One simple test is to use a per- naturally, my position play and patterns fectly circular hole just a little larger than the evolved to where I was using draw on most ball and make sure there is a constant clear- shots. ance all around the ball no matter which way Eventually, I got up enough courage and it's turned in the hole. funds to make a trip to the local poolhall to One tool I've seen in a billiard-supply try my luck in a competitive match. The cue store is a stand where the ball sits on three ball there looked a little funny. It seemed ball bearings while a feeler gauge touches big. It seemed rough, as if someone had the top of the ball. As you rotate the ball on taken sandpaper to the surface. Maybe it the bearings, the feeler gauge indicates how was a big barbox cue ball that had migrated many thousandths of an inch the top of the to a regular table, or perhaps it was an old, ball moves up and down. One precise tech- mud break ball. In any case, it didn't draw. I nique scientists use is to measure the devia- was helpless. The local hotshot would miss tion from roundness of a bunch of "great cir- until the last three balls, because he quickly cles" around the alleged sphere. A great cir- figured out there was no way I could get cle is a circle on the surface of a sphere that position two shots in a row. I didn't have my has the same diameter as the sphere, divid- rent money with me, so the lesson that day ing it into two equal hemispheres, like the was worth more than the price, although it equator on the Earth. Mathematical tech- took me a while to figure out what the les- niques allow scientists to connect the circles son was. cial lathe to make it "true" again, and the together to find the topography of the I've mentioned here before that cue balls balls became smaller and smaller. sphere, accurate to about 1 part in 10 mil- can also be off-center or out of round. You Trying to test the roundness of a pool ball lion. I think for the purposes of pool, just may notice this when the ball is rolling a is far harder than testing the size. You might watching for inconsistent roll-off as the ball long way to a stop. One time it might roll a measure a bunch of diameters of the ball, but comes to a stop is good enough. little to the left. The next, along the same even if they are all the same, you can't be Should you worry about all of the above? path, it might roll to the right. Back when sure that the ball is really round. Look at the Only when your game is ready for these ivory was the preferred material for carom two-dimensional shape in Diagram 3. details, such as when you can control the roll balls, this sort of behavior was fairly com- Measure its "diameters" or the distances of the cue ball to better than one diamond. POCKET REPRODUCTION

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