Summary: Billiards Digest December, 2011
"Draw Shot Cue Ball Directions" ILLUSTRATED PRINCIPLES
David Alciatore, PhD ("Dr. Dave")
Supporting narrated video (NV) demonstrations, high-speed video (HSV) clips, and technical proofs (TP),
and all of my past articles, can be accessed and viewed online at billiards.colostate.edu. The reference
numbers used in my articles will help you locate the resources on the website. If you have a slow or
inconvenient Internet connection, you might want to view the resources from a CD-ROM or DVD. Details
can be found online at: dr-dave-billiards.com.
Last month, we looked at several systems useful for predicting the direction the cue ball (CB) heads after
striking the object ball (OB). These systems apply only for follow shots, where the CB is rolling into the OB.
This begs an obvious question: Do such systems exist for draw shots also? The answer is yes, and that's
the topic of this article.
In my March '06 article, I presented the trisect (3X) system, which is very useful for predicting CB
direction with "good-action" draw shots. As illustrated in Diagram 1, the trisect system predicts that the final
CB direction angle, relative to the original CB direction, will be three-times the cut angle. NV B.67 illustrates
how you can use your hand to visualize both the cut angle (A) and 3-times the angle (3A). Alternatively, as
illustrated by the small cues and blue arcs in Diagram 1, you can use your cue to estimate the angle by
rotating it from the line of aim to the line-of-centers, and then rotating it the same amount two more times to
find the predicted CB direction. For more info and demonstrations of the trisect system, see "draw" in the
FAQ section of my website.