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+ T E C H

T A L K +

BY Bob Jewett

SCRATCHED TO DEATH

N MY S e p t e m b e r c o l u m n , I d i s c u s s e d t h e fact t h a t c e r t a i n o b j e c t - b a l l p o sitions on the table were very likely to lead to scratches. O n e example was a semicircle t h a t sits s p a n n i n g t h e e n d rail. If a ball is on that arc (or n e a r it), a n d y o u p o c k e t it in o n e of the foot p o c k e t s w i t h n o d r a w o r follow, t h e c u e ball is s u r e to scratch in the o t h e r foot pocket. After s u b m i t t i n g that column, I rem e m b e r e d seeing some other d i a g r a m s a b o u t a similar idea. In the 1925 book "English James Billiards Ogden Made shows Easy," Diaparts of circles (arcs). O g d e n ' s d i a g r a m s have t w o n e w features. First, o n e e n d of the arc is at the c u e b a l l s location. T h i s isn't o b v i o u s from t h e balls s h o w n in the diagram, but you can m o v e the object ball closer a n d closer to the cue b a l l a n d still h a v e a m o r e o r l e s s a u tomatic scratch with the right kind of c u e i n g a n d c u t a n g l e . T h e o t h e r difference is the total curve of the arc or the a m o u n t o f a full c i r c l e t h a t i t i n c l u d e s , coming

More geometry to keep your cue ball free from a dangerous fall.

grees. This angle is very insensitive to h o w full t h e o b j e c t b a l l i s s t r u c k , s o for a large r a n g e of cut angles on t h e object ball, t h e c u e ball will deflect close to 30 degrees to the other side. This constant angle off t h e of the cue ball is exactly object ball

w h a t is n e e d e d at E n g l i s h Billiards. If the cue ball h a p p e n s to be in the right position, or you can place it in the right position because it is in hand, you can play a half-ball hit a n d be sure that t h e cue ball will h e a d for t h e p o c k e t . It turns out that the angle t h e c u e ball is deflected for a half-ball hit is n o t q u i t e 30 degrees but rather 35 degrees (within a on the fraction of charactertheir the a degree). depends istics weights, T h e exact angle balls -- smooth

g r a m s 1 a n d 2. In Diagram 1, he s h o w s various places from w h i c h t h e cue ball c a n scratch if it starts in the " D " on a s n o o k e r table. (In those d a y s , t h e y w e r e called "billiards" tables, because was the m a i n game played on t h e m professionally billiards and not snooker.) In E n g l i s h Billiards, o n e of the main ways to score is to s c r a t c h off o n e o f t h e o t h e r two balls. You get two or t h r e e p o i n t s for t h a t , a n d g e t to take y o u r c u e ball to the D a n d shoot again. R e m e m b e r that this is on a table that is 6-by-12-feet in size. F o r a ball sitting in the right place, the scratch is much, m u c h easier than pocketing t h e ball. T h e real trick to that part of English Billiards, called which turns out to be 70 degrees. W h y is that? Those of you who have been reading Dave Alciatore's recent columns (and m y c o l u m n s a n d Bob Byrne's c o l u m n s before that) s h o u l d k n o w about the 30degree rule. If the cue ball strikes the o b j e c t b a l l a b o u t h a l f full a n d i s r o l l i n g s m o o t h l y at contact, it will be deflected from its o r i g i n a l p a t h b y r o u g h l y 3 0 d e 2 00 7 "in-offs" b e c a u s e the c u e ball goes i n t o a p o c k e t off a b a l l , is to r e c o g n i z e t h o s e special l o c a t i o n s that are nearly certain to scratch. That knowledge is exactly what you need to avoid scratching w h e n playing pool. I n D i a g r a m 1 , O d g e n s h o w s s h o t s for w h i c h a scratch is not only possible, b u t easy. J u s t a s w i t h S e p t e m b e r ' s d i a g r a m s , the locations of the object balls form

of t h e how

surfaces are, h o w elastic the plastic is -- a n d y o u h a v e to e x p e r i m e n t on the table to b e p r e c i s e . You'll n e e d t o d o that anyway, once you finish t h i s article, to get a feeling for t h e a n g l e . W i t h t h e c u e ball deflected 35 degrees on a s h o t , g e o m e t r y tells us that the resulting arc will be twice thai, or 70 degrees out of a c i r c l e . F r o m this idea, O g d e n produced the figure in Diagram 2. T h i s l o o k s like the chalk o u t l i n e of a large, w i n g e d , aquatic space alien w h o was m u r d e r e d on a s n o o k e r tab l e , b u t it's a c t u a l l y m u c h m o r e u s e f u l t h a n t h a t . I t i s t h e r e g i o n o f all p o s s i b l e locations of an object ball w h e r e you c a n set up an easy half-ball scratch from t h e D . T h e a l i e n ' s feet a r e m a d e u p f r o m two 70-degree arcs that have their o t h e r ends at the corners of the D. As an exa m p l e , n o t e that the foot s p o t , w h a t the British call t h e p y r a m i d s p o t o r t h e p i n k spot, is within the body. This means

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BILLIARDS DIGEST

November

t h a t t o s c r a t c h off a b a l l a t t h a t l o c a t i o n , the c u e ball is placed s o m e w h e r e w i t h i n the D a n d played with s m o o t h , rolling f o l l o w w i t h a h a l f - b a l l h i t off o n e s i d e o r t h e o t h e r of the object ball. G o t o a table n o w a n d find w h e r e y o u have to place the cue ball on the h e a d string to easily s c r a t c h off a b a l l o n t h e f o o t spot. If O g d e n ' d i a g r a m is s r i g h t e n o u g h for a p o o l t a b l e , that spot s h o u l d be within a few i n c h e s of t h e h e a d spot. At English Billiards, one w a y to r u n up a lot of p o i n t s w a s t o s c r a t c h off a b a l l i n the scratch area a n d drive the b a l l off s o m e c u s h i o n s b a c k into that area. Top players bringing the got very good at doing that repeatedly, always the object ball b a c k to

t h e y m e e t at a p o i n t

about

6 inches

a slowly rolling c u e ball a n d n o t s c r a t c h . T h e e x a c t p o i n t m i g h t b e a l i t t l e forward or back from the illustrated spot, b u t there is s u c h a p o i n t . T h e last t h i n g to n o t e is that if the object ball is on the centerline of the table b u t on y o u r side of the p o i s o n e d p o i n t , it is again h a r d to scratch while m a k i n g the object ball, as t h e c u e ball will always land on the side cushion. Try c o n s t r u c t i n g y o u r own say, scratching for the cue a arc, ball foot to

a b o v e t h e foot s p o t . F o r t h e p u r p o s e s o f play, t h i s m e a n s t h r e e t h i n g s . I f t h e object ball is on the other side of the a r c s ( o n t h e f o o t s p o t , for e x a m p l e ) , i t is hard to scratch as long as you shoot

near a head pocket and scratching pocket. into Remember

always try to hit the o b j e c t b a l l h a l f full a n d let the cue ball roll on the cloth with just a slowly a n d the cue ball is rolling w h e n it gets to the object ball. T h e c u e ball will go to the foot rail. T h e s e c o n d is that if t h e object ball is at t h e i n t e r s e c t i o n , m a r k e d as the "poisoned point of double d e a t h , " there is no w a y to m a k e the object ball in either corner p o c k e t w i t h little m o r e speed than required to get to the pocket. T h a t will e n s u r e a true half-ball carom angle. K n o w i n g t h e arcs a n d a n g l e s for t h e s e nearly certain scratches will h e l p k e e p y o u -- a n d y o u r c u e ball -- o u t of t r o u ble.

same spot, so the rules were changed to require s o m e o t h e r s h o t from time to time. In D i a g r a m 3 is a s i m i l a r s i t u a t i o n for a p o o l table. T h e cue ball is on the h e a d s p o t . T h e " a r c s o f d i s a s t e r " for s c r a t c h ing in p o c k e t s A a n d B are m a r k e d a n d

November

2007

BILLIARDS DIGEST

33

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