PDA

View Full Version : David Alciatorre-30, 90 degree rules

Wally_in_Cincy
07-03-2004, 11:52 AM
Has anybody been reading David Alciatorre's columns in BD about his 90-degree and 30-degree rules?

I'm sure I had read about this before (maybe it was not as clearly written elsewhere) but after reading his last 3 columns it finally got thru my thick head. Putting these into practice has really helped my position play.

If you don't subscribe to BD he has a website that includes videos. I don't have the link handy. If nobody has it I can post it next week.

DialUp
07-03-2004, 12:48 PM
Understanding the 30 and 90 degree rules will improve your game overnight. Have fun with the new power you just unlocked /ccboard/images/graemlins/smile.gif

Here is the link to the free online videos, BTW

http://www.engr.colostate.edu/~dga/pool/normal_videos

Frank_Glenn
07-03-2004, 03:05 PM
<blockquote><font class="small">Quote DialUp:</font><hr> Understanding the 30 and 90 degree rules will improve your game overnight. Have fun with the new power you just unlocked /ccboard/images/graemlins/smile.gif

Here is the link to the free online videos, BTW

http://www.engr.colostate.edu/~dga/pool/normal_videos <hr /></blockquote>

I built a demo tool to show how the 90° line works. You can see it on my web page:
www.frankglenn.com (http://www.frankglenn.com)

It's made of 1/2" PVC pipe and is very good for demonstrating the difference between stun (sliding, which gives the 90° line), draw, and follow which deviate from the 90° line.

larrynj1
07-03-2004, 03:33 PM
i've been aware of the 30 degree rule for awhile, but was not comfortable in estimating the angle in my mind. the suggestion of forming a "v" with your fingers, or a peace symbol for the ex-hippies, helped me out a lot.

woody_968
07-03-2004, 04:40 PM
Interesting site, thanks for the link.

Pelican
07-03-2004, 07:07 PM
<blockquote><font class="small">Quote larrynj1:</font><hr> or a peace symbol for the ex-hippies <hr /></blockquote>

Yo Larry dude, got a toke man? ................. /ccboard/images/graemlins/grin.gif

dmgwalsh
07-04-2004, 06:19 AM
<blockquote><font class="small">Quote Frank_Glenn:</font><hr>

I built a demo tool to show how the 90° line works. You can see it on my web page:
www.frankglenn.com (http://www.frankglenn.com)

It's made of 1/2" PVC pipe and is very good for demonstrating the difference between stun (sliding, which gives the 90° line), draw, and follow which deviate from the 90° line. <hr /></blockquote>

I saw Tim White use one of these on his videos. Do you use it for teaching or practicing or what?

Frank_Glenn
07-04-2004, 06:44 AM
[ QUOTE ]

I saw Tim White use one of these on his videos. Do you use it for teaching or practicing or what? <hr /></blockquote>

I have his videos (they're pretty good, in fact). I saw it in them and made it to see if I could. I am not an instructor, but I have used it to show others in league the 90° line. His was fancy and made of copper pipe. I saw it in person a VF a couple of years ago (this is when I got the tapes) when his booth was next to the one I was working in.

pooltchr
07-04-2004, 08:02 AM
Wally,
It's a great set of articles. The important thing to remember is the 90 degree rule is 90 degrees from the point of contact with the ob. The 30 degree half ball hit is 30 degrees off the original line of travel of the cb, not 30 degrees off the contact point.

Frank,
I like your demo tool a lot. I'm considering taking it a step farther and putting a half circle of plexiglas on top of it and marking it off like a protractor. I think some of the more advanced students could use it to determine the cb travel path based on various degrees of cut angles. Just a thought.
Steve

Frank_Glenn
07-04-2004, 08:55 AM
[ QUOTE ]

Frank,
I like your demo tool a lot. I'm considering taking it a step farther and putting a half circle of plexiglas on top of it and marking it off like a protractor. I think some of the more advanced students could use it to determine the cb travel path based on various degrees of cut angles. Just a thought.
Steve <hr /></blockquote>

Excellent idea! I'll do that myself. I'll add a picture of it to the web page. I even have a piece of plexiglass I can use.

randyg
07-05-2004, 04:01 PM
Hey pooltchr: Let's have some fun here.

First; I thought the 90 degrees was from the point of release, not contact (picky picky picky).

Second; The OB has no idea where the cue ball comes from, until contact. No matter what angle of attack from the cue ball, after release it will always start it's travel at 90 degrees....randyg

pooltchr
07-06-2004, 05:48 AM
<blockquote><font class="small">Quote randyg:</font><hr> Hey pooltchr: Let's have some fun here.

First; I thought the 90 degrees was from the point of release, not contact (picky picky picky).

Second; The OB has no idea where the cue ball comes from, until contact. No matter what angle of attack from the cue ball, after release it will always start it's travel at 90 degrees....randyg <hr /></blockquote>

Randy,
If there is one person on this board I would hesitate to get into this discussion with, it's you! /ccboard/images/graemlins/wink.gif On the other hand, I know that if I am not clear on a subject, I can count on you to keep me straight, so let me try to clarify.

From what I understand, when the cb and ob make contact at anything other than straight on, the initial movement of the cb will be at 90 degrees from the line of centers (the line between the center of both balls at the time of contact). If the cb has no forward or backward spin at the time of contact, it will continue on the same line (tangent line). With forward spin, it will move off the tangent line on a more forward line, and with back spin, it will pull the cb back off the tangent line.
Second, the ob will travel in the opposite direction from the point of contact along the line of centers regardless of the line of attack from the cb, with a slight adjustment forward of that line due to "kling".

The artiicle as I read it says that after a half ball hit, the path of the cb with forward roll will move off approximately 30 degrees after contact. I would think that the initial path would still take it along the tangent line until the forward roll has a chance to alter the path. (how'm I doin' so far?)

I haven't tested this theory myself, which is why I am looking at Frank's tool modified as I suggested. If I get it put together in time, maybe we can do some testing of this theory the next time we get together.

Qtec
07-06-2004, 08:27 AM
Wally, you have surely read about this on this forum, 50 times. The 90/30 rules are the basis for positional play.
In snooker circles the 30 degree rule is know as 'the natural angle'.
Its really the first thing that should be learned!

If you would take a lesson from an instructor, all will be revealed. /ccboard/images/graemlins/grin.gif

Qtec

SPetty
07-06-2004, 01:45 PM
<blockquote><font class="small">Quote Qtec:</font><hr>Wally, you have surely read about this on this forum 50 times. The 90/30 rules are the basis for positional play.
In snooker circles the 30 degree rule is know as 'the natural angle'.
Its really the first thing that should be learned!

If you would take a lesson from an instructor, all will be revealed. /ccboard/images/graemlins/grin.gif<hr /></blockquote>Hi Qtec,

Don't be so sure. I've read here about the 90 degree rule a lot and I've seen it in books and videos and from instructors.

I've heard little, if anything, about the 30 degree rule. I can only guess that it is a closely guarded secret and is obviously the reason I can't aim. /ccboard/images/graemlins/wink.gif

It seems to me that these two "rules" contradict each other, but it does help explain why I can't seem to count on the 90 degree rule! It looks like the 90 degree rule is OK until the 30 degree rule comes into play. It also seems from the web page instruction, that the 30 degree rule comes into play for all hits between just before a 1/4 ball hit to just after a 3/4 ball hit. /ccboard/images/graemlins/confused.gif

DialUp
07-06-2004, 03:34 PM
<blockquote><font class="small">Quote SPetty:</font><hr>

It seems to me that these two "rules" contradict each other, but it does help explain why I can't seem to count on the 90 degree rule! It looks like the 90 degree rule is OK until the 30 degree rule comes into play. It also seems from the web page instruction, that the 30 degree rule comes into play for all hits between just before a 1/4 ball hit to just after a 3/4 ball hit. /ccboard/images/graemlins/confused.gif
<hr /></blockquote>

The rules are quite simple.

90 Degree - when the CB is sliding.

30 Degree - When the CB is rolling.

If the CB is rolling when it hits the OB, it will deflect at a 30 degree angle from its original path.

If the CB is sliding when it hits the OB, it will deflect at 90 degrees from the contact point of the CB and OB.

The link I posted above has example of the different variations like top spin, back spin, and speed.

Frank_Glenn
07-06-2004, 05:03 PM
[ QUOTE ]

The rules are quite simple.

90 Degree - when the CB is sliding.

30 Degree - When the CB is rolling.

If the CB is rolling when it hits the OB, it will deflect at a 30 degree angle from its original path.

If the CB is sliding when it hits the OB, it will deflect at 90 degrees from the contact point of the CB and OB.
<hr /></blockquote>

I agree that it is 90° when the cueball slides into the object ball. The angle when rolling changes with the amount of spin for me. 30° is a half ball hit, which will still result in the 90° tangent line if the cueball is sliding. One (30°) is angle in, the other (90°) is angle out. YMMV

Qtec
07-06-2004, 07:27 PM
[ QUOTE ]
It seems to me that these two "rules" contradict each other, but it does help explain why I can't seem to count on the 90 degree rule! It looks like the 90 degree rule is OK until the 30 degree rule comes into play. It also seems from the web page instruction, that the 30 degree rule comes into play for all hits between just before a 1/4 ball hit to just after a 3/4 ball hit.
<hr /></blockquote>

Most people who have difficulty with the 90 degree angle dont hit the Qball properly. You could try this simple practice.

wei (http://endeavor.med.nyu.edu/~wei/pool/pooltable2.html)

START(
%AO0O4%IL4^8%OG8^2%PW2W6%QX3W1%RQ3W7%UP1Q5%VR5W1%W B9C0%XW0W5
%][3D0%^O7P4
)END

Shot 1: Using a medium stroke and good follow thru, shoot the 1ball into pocket A and stop the Qball dead. You should be hitting the Qball just below center.
Once you are consistently getting the Qball to stop, move the Qball to position B. Now hit the Qball in exactly the same way as you did for the stop shot and you will find the Qball now heading towards the middle pocket.
If you can pocket the 1 ball in the corner and the Qball in the side, you will be hitting the Qball in the right way.

The 30 degree rule is a rough estimate. Once you are hitting the OB real thin, you will get slightly less than 30 degrees, but I wouldnt to worry about that now. /ccboard/images/graemlins/laugh.gif
Qtec

SpiderMan
07-07-2004, 09:08 AM
SPetty,

It isn't actually 30 degrees, but a little bit wider for a half-ball hit, and less for thick or thin hits. Probably 30 degrees is just an easy approximation to remember. See Robert Byrne's or Jack Koehler's books for some further reading, I think both have discussed this.

If you can't depend on the 90-degree rule, it's probably that your cueball isn't sliding at the moment of contact. If it arrives with any top or bottom, the cueball will take the 90-degree path initially, but will "bend" to a new path dictated by follow or draw.

To get a true 90 degrees, the cueball must be played such that it would produce a dead stop if it hit the object ball full, ie a "stop shot" cueing, except you are cutting the ball.

SpiderMan

wolfdancer
07-07-2004, 12:29 PM
Steve, do "advanced" students really need a teaching aid this intricate to visualize a 90 angle???

SpiderMan
07-07-2004, 01:40 PM
There are several ways to visualize this, and we're all probably thinking the same thing but expressing it differently.

My own method is to imagine the cue ball and object ball at their locations corresponding to the instant of contact. From that "frozen" visualization, the object ball moves away along the line through their centers (which also intersects the contact point) and the cueball initially moves exactly 90 degrees away from that line (parallel to the line which forms a common tangent between the two balls).

Since both the common center line and the common tangent line also pass through the contact point, an alternate visualization is to imagine two lines crossing in a 90-degree "+" from above, centered at the contact point with one line going through the centers and the other line positioned as the tangent. The center of the object ball takes one line, the **EDGE** of the cueball takes the other.

For those prone to nitpick, I qualify the above as neglecting second-order effects such as cling, differential masses or diameters, etc /ccboard/images/graemlins/wink.gif

SpiderMan

Bob_Jewett
07-07-2004, 02:08 PM
<blockquote><font class="small">Quote Wally_in_Cincy:</font><hr> Has anybody been reading David Alciatorre's columns in BD about his 90-degree and 30-degree rules?

I'm sure I had read about this before (maybe it was not as clearly written elsewhere) but after reading his last 3 columns it finally got thru my thick head. Putting these into practice has really helped my position play. <hr /></blockquote>

The 90-degree rule (inital path of the cue ball after collision is perpendicular to the path of the object ball) is discussed by pretty much every pool/billiard book in existence, I think.

Actually, there are a couple of small corrections to the rule. If the cue ball is off the surface of the table when it contacts the object ball, it will tend to go forward of the 90-degree line. To the extent that the cue ball is inelastic (by the technical definition of elasticity) it will go forward of the 90-degree line. If throw is involved in the shot, the angle of separation may be slightly more or less than 90, but it is the object ball that is changed by this effect and the cue ball will still travel at a 90-degree line to the line of centers at the moment of contact.

As for the "30-degree" rule, you may want to look at Byrne's treatment in "Advanced Technique". I think it is important to note that the actual angle is not 30 degrees. If you have old copies of Billiards Digest, see articles in the February 1997 and November 2000 issues for some more aspects of the shot. I learned about the half-ball angle from books about English Billiards, a game at which the shot is essential, and which is one of the great disciplines of cue sports.

Bob_Jewett
07-07-2004, 02:24 PM
If you would like a general system for the angle a following cue ball will take, one was described in the December 1998 issue of Billiards Digest. It gives the exit angle for a cue ball that's rolling smoothly at contact for any cut angle with a fairly simple construction that you can actually use on the table. A much simpler system -- you could call it the "three-times angle system" -- which works for nearly full hits was described in the December 1995 issue.

pooltchr
07-07-2004, 02:57 PM
<blockquote><font class="small">Quote wolfdancer:</font><hr> Steve, do "advanced" students really need a teaching aid this intricate to visualize a 90 angle??? <hr /></blockquote>
Most probably don't, but some very good players have a hard time understand what 90 degrees looks like. People learn in different ways, some just need to hear it, some need to see it, some need to do it themselves. Any tool that addresses the visual realm is very handy for an instructor. Might not need it for every student, but for the ones that are visual learners, it's a nice thing to have.
Steve

woody_968
07-07-2004, 03:13 PM
<blockquote><font class="small">Quote pooltchr:</font><hr> People learn in different ways, some just need to hear it, some need to see it, some need to do it themselves. <hr /></blockquote>

IMO understanding this is a must for an instructor. Sometimes you need to say the same thing four different ways, or show it in a different manner in order to get it to "click" with the student.