Position Control

• 30-degree and 90-degree rules
• 45-degree rule for center-table position and routes
• leaving an angle on a shot and coming into the line of a shot
• nearly straight-in shots
• position control drills
• rail cut-shot 60-degree rule
• scratch avoidance
• speed effects
• target practice drills
• useful reference lines
• wagon wheel drills
• where the CB goes for different cases

for more information, see Chapter 5 in The Illustrated Principles of Pool and Billiards,
Disc I and Disc II of the Video Encyclopedia of Pool Shots (VEPS) , and
Disc I and Disc II of the Video Encyclopedia of Pool Practice (VEPP)

45-degree rule for center-table position and routes

What is the 45-degree rule, and how is it used to position the CB at or through the center of the table?

It states that if the CB rolls into the short rail at close to a 45-degree angle, it will head of two rails fairly close to the center of the table. For more info, see the following demonstration from Disc II of the Video Encyclopedia of Pool Shots:

See my March '10 Billiards Digest article for more information.

Here's a good drill from Disc II of the Video Encyclopedia of Pool Practice (VEPP) for practicing getting to the center of the table off pocket hangers:

leaving an angle on a shot and coming into the line of a shot

How do I do this?

See the following demonstration from Disc II of the Video Encyclopedia of Pool Shots:

Sometimes, it is important to play for a precise point or line, rather to a general area. Here's an example from Disc III of the Video Encyclopedia of Pool Shots:

nearly straight-in shots

How can I get position on the next shot if the current shot is nearly straight in?

See: NV B.30 - Cue ball position control with nearly straight-in shots.

rail cut-shot 60-degree rule

How can I predict final cue ball direction for rail cut shots?

For rolling-cue-ball rail cut shots, you can use the 30-degree rule, as illustrated in the diagram below. The peace sign can be used to visualize the expected angle off the OB if the rail were not there, and the mirror of this angle gives you the final cue ball direction. An interesting fact is that the sum of the angle of the initial CB line relative to the rail and the mirror angle relative to the rail normal always adds to 60 degrees (see the quote from mohrt below). This is because 90 - 30 = 60.

English can be used to alter the path. Also, using stun or draw or less than full forward roll can also be used to alter the path.

from mohrt:

If you come into the rail at 30 degrees, the path will be 30 degrees out. If you come in at 15 degrees, it will be 45 degrees out. If you come in at 25 degrees, it will be 35 degrees out. Notice it always adds up to 60 degrees.

scratch avoidance

How do I avoid a scratch in different situations?

See the following video demonstrations:

• NV 3.7 - Using the 90° rule to check for and prevent a scratch
• NV 3.10 - Using the 30° rule to check for and prevent a scratch
• NV 4.2 - Using a draw shot to prevent a scratch
• NV 4.5 - Using a follow shot to prevent a scratch
• NV 4.22 - Avoiding a tangent-line scratch using slow speed
• NV B.25 - Using draw and English to beat a scratch in a side pocket, with Tom Ross
• NV B.31 - Using inside English and follow to beat a scratch and get down-table position
• NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) examples
• HSV B.12 - Beating a scratch by bouncing the cue ball off the rear rim of a pocket

speed effects

What effect does shot speed have on the 90-degree and 30-degree rules?

Shot speed has no effect on the 90-degree rule. With a stun shot, the CB heads straight down the tangent line, regardless of speed.

With follow and draw shots, the CB persists along the tangent line longer before curving to the final direction, as demonstrated in this video:

For more information, including the effects of cue elevation, see: HSV B.23 - cue ball path speed, spin, and cue elevation effects.

When using the 30-degree rule, this diagram shows how you need to shift the peace-sign down the tangent line with faster speeds, to predict the final CB direction:

For more information, see my June '05 article.

With draw shots, a similar shift with speed occurs, based on this diagram:

For more information, see my January '06 article.

The condition of the cloth also has an effect. With a slicker cloth, the CB persists along the tangent line longer before curving to the final direction. For more info, see cloth effects.

useful reference lines

How can I know where the cue ball will go on every type of shot?

See:

• NV B.43 - Cue ball position control stun, roll, and draw reference lines
• NV B.44 - Dr. Dave 30-degree-rule peace-sign hand calibration
• NV B.45 - Cue ball path speed effects
• NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) examples
• NV B.60 - Mike Page's Cue Ball Control
• NV B.66 - The 30-degree rule, from VEPS I
• NV B.67 - The trisect system for draw shots, from VEPS I

Here's an example from Disc I of The Video Encyclopedia of Pool Shots where the reference lines can be useful to plan cluster break-out shots:

For more info, see:

• where the CB goes for different cases
• my January '09 and February '09 BD articles on this topic

where the CB goes for different cases

Where will the cue ball go after it hits an object ball?

For a stun shot, most people know the right answer: in the tangent line direction, perpendicular to the OB direction. This is the 90-degree rule (see my Jan '04 article). If you want a more precise answer that accounts for various effects (e.g., friction and English), see my March-June '05 articles. FYI, here is a convenient one-page summary of the 90-degree rule.

For a rolling CB, the cue ball changes direction by about 30 degrees for a wide range of cut shots (1/4 to 3/4 ball hit). This is the 30 degree rule (see my April '04 article). If you want to be more precise, the angle is a little more (about 34 degrees) closer to a 1/2-ball hit and a little less (about 27 degrees) closer to a 1/4-ball or 3/4-ball hit. If you want to know how to account for speed effects, see my June '05 article. If you want an easy way to use your hand to accurately visualize the cue ball direction, use the Dr. Dave peace-sign technique. FYI, here is a convenient one-page summary of the 30-degree rule.

For a draw shot with good draw action, and for cut angles smaller than about 40 degrees (i.e., ball-hit fraction greater than about 3/8), the trisect system is your answer (see my March '06 article). You can use a modified version of the Dr. Dave peace-sign technique to predict the cue ball direction (see the article, NV B.43, and NV B.67 for illustrations and examples).

For shots "in between" all of these different cases, the cue ball will go somewhere in between the indicated directions. The only way to get a feel for how much "in between" the cue ball will go is to practice ... a lot!

To see how speed affects CB trajectories, see speed effects.

For more info, see Disc I and Disc II of the Video Encyclopedia of Pool Shots and:

• NV B.43 - Cue ball position control stun, roll, and draw reference lines
• NV B.44 - Dr. Dave 30-degree-rule peace-sign hand calibration
• NV B.45 - Cue ball path speed effects
• NV B.46 - Cue ball path scratch avoid, cluster break-out, and billiard (carom) example
• NV B.60 - Mike Page's Cue Ball Control
• NV B.66 - The 30-degree rule, from VEPS I
• NV B.67 - The trisect system for draw shots, from VEPS I
• NV B.68 - Tweener cluster breaks, from VEPS I
• NV B.75 - 30-degree-rule natural-angle examples, from VEPS III
• my January '09 and February '09 BD articles on these topics

See also:

• the 60-degree rule for rail cut shots.
• Ralph Eckert's lessons on natural-roll position-play reference lines (part 1, part 2, part 3)

What if the cut is very thin or hit very full?

For roll shots, there are good approximations for the CB deflection angles.

For a fairly full hit, with a ball-hit-fraction greater than 3/4, the CB will deflect about 3-times the cut angle.

For a fairly thin hit, with a ball-hit-fraction less than 1/4, the CB will deflect about 70% of the angle between the aiming line and the tangent line.

See my November '11 Billiards Digest article for illustrations, examples, and more information.

There are similar rules for draw shots. For more information, see my December '11 Billiards Digest article.

As with the 30 degree rule and trisect system, the full-hit and thin-hit rules apply to the final direction of the CB. The actual final path of the CB is shifted down the tangent line with higher speed.

Video demonstrations of these types of shots can be found in Disc I of the Video Encyclopedia of Pool Shots.

from Jal (from AZB post, which contains additional information):

When the balls are close enough to each other and/or you're hitting hard enough such that the cueball doesn't lose any significant backspin on the way to the object ball (or gain more topspin), there is a method of determining the cueball's direction once it reaches natural roll after the collision. I call it the Bottom-Center-Arrow method, or B-C-A for short, in that it's easy to remember.

Imagine a circle centered on the ghostball with the bottom of the circle running through the center of the cueball. This circle represents the face of the cueball from the shooter's perspective. To determine the CB's roll direction after the collision for any vertical offset (no sidespin applied), draw a line from the center of the real cueball parallel to the line of centers between the ghostball and the object ball. This will intersect the tangent line at 90 degrees, call it point A. Thus, we have a triangle with the CB at vertex B (bottom of the circle), the ghostball at C (center of the circle) and point A from which we'll draw an arrow such that it intersects the vertical axis of the large circle. This yields the CB's direction once roll sets in, given that vertical tip offset on the face of cueball. Here's a diagram:

... friction, amongst other things, has an effect on this idealized geometry.