Pivot Point
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Pivot Point - Graphic Explanation
FROM THE A/V DEPARTMENT: SOME BASICS ABOUT THE PIVOT POINT.
MEASURING PIVOT LENGTH:
A shaft's pivot length is the distance the CB travels to be offline exactly the amount of sideways tip offset. It's different for different shafts, but for each shaft there's one pivot length for all tip offsets. The example in the picture assumes a pivot length of 1 diamond (12.5 inches) for illustration purposes.
ADJUSTING FOR SQUIRT:
Pivoting your shaft at it's pivot length (pivot point) to apply sidespin makes the shaft duplicate the CB squirt angle in the opposite direction, adjusting for squirt to send the CB along the original shot line.
Find your cue's pivot point, pivot there, make shots/get shape. Simple, right? Well, except for swerve, which changes the "effective pivot point" for every shot. But that's another chapter.
pj
chgo
FROM THE A/V DEPARTMENT: SOME BASICS ABOUT THE PIVOT POINT.
MEASURING PIVOT LENGTH:
A shaft's pivot length is the distance the CB travels to be offline exactly the amount of sideways tip offset. It's different for different shafts, but for each shaft there's one pivot length for all tip offsets. The example in the picture assumes a pivot length of 1 diamond (12.5 inches) for illustration purposes.
ADJUSTING FOR SQUIRT:
Pivoting your shaft at it's pivot length (pivot point) to apply sidespin makes the shaft duplicate the CB squirt angle in the opposite direction, adjusting for squirt to send the CB along the original shot line.
Find your cue's pivot point, pivot there, make shots/get shape. Simple, right? Well, except for swerve, which changes the "effective pivot point" for every shot. But that's another chapter.
pj
chgo
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devindra said:
Whenever you use sidespin you get three effects:
1. Sidespin (duh)
2. Squirt
3. Swerve (a "mini masse" from hitting down on the ball with sidespin)
Swerve curves the CB in the opposite direction from squirt, so "in effect" it reduces squirt (increases the "effective" pivot length). That would be a good thing if it was consistent, but unfortunately it isn't, so it's a bad thing. In fact, it's the real difficulty with sidespin. The amount of swerve changes with the amount of sidespin and with the distance and speed of the shot (not to mention the cue's butt elevation and ball/cloth condition).
So the only way you can "determine" the effective pivot point for each shot is by practicing and getting a feel for the adjustment that has to be made for swerve depending on how you hit each shot:
Slower / longer shots = more swerve / less "effective" squirt / longer "effective pivot point"
Faster / shorter shots = less swerve / more "effective" squirt / shorter "effective pivot point"
pj
chgo
Devindra,devindra said:
If you want a really rough guide to working out your effective pivot point try this little formula.
Based on say a 'PURE' Pivot Point of 10". This is your baseline (shortest) bridge length.
Now add to this V x D x 0.3
0.3 = CFF = cloth friction factor
Where V = Velocity Rating ... 1= Top Speed. 5 = Slow (rolls about one table length). (Note that slower gives a higher number and the lowest number is 1.)
D = Distance in diamonds between CB and OB. Most the time you'll be playing these shots with less that 4 diamonds travel from CB to OB.
So, for a 2 foot (diamond) shot at medium-slow speed (4) you're looking at a bridge length around 10 + (2x4x0.3) = 12.4 Inches.
Hence, Effective Pivot Point = Pure Pivot Point + (V x D x CFF).
This doesn't take into account cloth slickness or cue elevation.
For a very slick cloth the cloth friction factor might be under 0.2, where a slow sticky cloth might be over 0.4.
This formula also assumes linearity, which won't always be true. On some shots the swerve might complete its arc early in the travel path. Other variables also mean it is not perfect, but it is a handy guide and should put you within an inch of the required pivot length for most shots, which should be accurate enough to make most shots.
Colin
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Yes, but learning approximately where the cue's "single" pivot point is located is good enough for most shots. I'm speaking of the cue's intrinsic pivot point here, not the swerve compensated one Patrick (great graphics!) and Colin are talking about. The fact that in theory it (the intrinsic PP) moves a little with different tip offsets shouldn't really come into play unless extreme accuracy is required. Don't sweat being a centimeter or two off. If extreme accuracy is required, it probably isn't a good idea to use english anyway. Sometimes you have to accept poor position to make the shot at hand.devindra said:
Sorry, but I'm not sure to which of Dr. Dave's methods you're referring.
Jim
It's something I developed myself.jondrums said:
A work in progress in terms of refining the constants and creating the best yet simplest formula.
Colin
devindra said:
It could be the effets of throw (though I doubt it). If you see the throw chart below, which is for 3/4 ball cut, slow-medium speed, IE is to the left, there is less throw for extreme side english than for moderate side english with IE for a sliding CB. If there is follow, the difference is less noticeable.
Note: Color bands represent inches per yard OB throw, compared to angle for natural rolling CB.
It might also be that you are swooping on the shots producing a touch of IE, in greater proportion than you are swooping when playing with extreme IE.
And we can't discount that the pivot point needs to be a little shorter for large offsets. I haven't tested this, but my experience suggests it is worth looking into. I find playing small offsets I sometimes don't get the squirt I'm expecting. I'm trying to work out some stuff based on Ron Shepard's paper.
Colin
Attachments
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Jal said:
This plus the adjustment always needed for swerve makes the Backhand English method another "approximation" aiming system - you use the system to get pretty close to the actual aim and then use your experience to "feel" the small adjustment necessary to make the shot. All aiming, with or without a system (and with our without sidespin), is like this.
pj
chgo
Patrick,Patrick Johnson said:
While there is feel involved in the application of BHE, in terms of the stroke speed, initial alignment, stoking straight and to the offset I'm aiming, the rest of the system I perform completely mechanically. I can look away from the OB after initial alignment and often do this during the stroke.
This has taken me quite a while to establish all the variables for each shot, but I can execute a wide range of shots accurately this way.
All I need to do is to calculate my effective pivot point for each shot, to account for the speed, swerve, cloth consdition, length from CB to OB; and to calculate my aim target, which I do by use of throw charts. Most common shots I can estimate the expected throw by memory within reasonable margins.
Regarding earlier pivot point tests, it seems to me they did not take into account approximately 3 degrees of throw, which led them to a shooting error of about 1/20th inch over 6-8 inches CB travel. This put many pivot point figures out about 30% (and more if played softer or with CB closer to OB) over true intrinsic values. I think the platinum data is therefore pretty accurate. It confirms to my experiments anyway.
Point is, not a lot has been available concerning the types of adjustments necessary, nor the nature of the intrinsic pivot point, so I do think a lot of people who use BHE have learned to adjust be a degree of feel on some shots. I guess they also have learned several shots where they've learned an adjustment that works and repeat this mechanically.
While the pre-pivot aiming can be feel based, I don't think BHE, if it is applied systematically, should be considered a feel system.
Colin
That's a pretty big "if". IF somebody is willing to go to the effort of applying your formula for swerve adjustment and IF the estimates built into the formula ("cloth friction factor" & velocity) turn out to be accurate for the shot and IF leaving cue elevation out of the calculation turns out to be OK, and IF all of this is accurately calculated by the shooter while at the table...
Sounds pretty "feely" to me.
pj
chgo
What do you mean by 'feely' Patrick?Patrick Johnson said:
With most shots where one might consider using english in normal play, I reckon the calculations I make, although imperfect are within the margins of error. I simply trust them and pivot and cue through the ball.
I know the difference between feel and using a system. I use feel to estimate my pot angle and for years most of my english use was entirely feel.
It is even possible to use a purely systematic way to aim for standard potting if one were to make enough measurements and have a systematic method of placing the bridge relative to the CB. However, I believe, except for robots such systems are unlikely to be practical.
But BHE, the way I use it is quite practical I believe. It is for me and I'm not using any feel post initial aim.
I think it sounds a lot trickier than it actually is once you adapt to the system and learn the appropriate adjustments.
btw: I don't find elevation to be a significant problem. When draw is used the shots are usually quite firm, hence swerve is not highly significant. Most shots that would seem ridiculous to attempt with normal english methods are also difficult using BHE.
Colin
natural pivot length
First, I will assume you measured the "natural pivot length" by eliminating or minimizing the effects of swerve and throw. In my November '07 article, I describe and illustrate a procedure you can use (along with recommendations to minimize swerve and throw as factors).
With a fast center-ball shot, if your bridge is not at the natural pivot length, and if you apply unintentional english (e.g., with poor alignment and/or a swooping stroke), then you might miss the shot. A good example of this is the break shot. If your bridge is at the natural pivot length, and if your aiming/alignment is good, you will get a square hit even if you swoop your stroke by accident (see Diagram 4 and the supporting discussion in my article).
When using English and FHE or BHE (see the article), the required effective pivot length will be different for every shot based on shot speed, ball distance, cue elevation, amount and type of english, and ball and cloth conditions. However, pivoting at the natural pivot length will account for squirt, provided you have already adjusted your aim for swerve and throw. For fast and short shots, swerve is not much of a factor. For new and slick balls, throw is not as big a factor. Squirt is always a factor. For more info, see:
and
Regards,
Dave
That depends on what type of shot you are talking about and how you measured the pivot point.devindra said:
First, I will assume you measured the "natural pivot length" by eliminating or minimizing the effects of swerve and throw. In my November '07 article, I describe and illustrate a procedure you can use (along with recommendations to minimize swerve and throw as factors).
With a fast center-ball shot, if your bridge is not at the natural pivot length, and if you apply unintentional english (e.g., with poor alignment and/or a swooping stroke), then you might miss the shot. A good example of this is the break shot. If your bridge is at the natural pivot length, and if your aiming/alignment is good, you will get a square hit even if you swoop your stroke by accident (see Diagram 4 and the supporting discussion in my article).
When using English and FHE or BHE (see the article), the required effective pivot length will be different for every shot based on shot speed, ball distance, cue elevation, amount and type of english, and ball and cloth conditions. However, pivoting at the natural pivot length will account for squirt, provided you have already adjusted your aim for swerve and throw. For fast and short shots, swerve is not much of a factor. For new and slick balls, throw is not as big a factor. Squirt is always a factor. For more info, see:
and
Regards,
Dave
bridge at pivot can be good for center-ball hits
Also, another example where the pivot point is important when not using BHE is when using FHE("front hand English"), or some combination of FHE/BHE, with a low-squirt cue that has a large pivot length.
Regards,
Dave
Even with center-ball hits, bridging at the natural (or effective) pivot point of the cue can be beneficial. A good example is the break shot (see Diagram 4 and the related discussion in my November '07 article.Colin Colenso said:
Also, another example where the pivot point is important when not using BHE is when using FHE("front hand English"), or some combination of FHE/BHE, with a low-squirt cue that has a large pivot length.
Regards,
Dave
CTE Feel it or approximate it, the ball still goes center pocket.
accurate "natural pivot length" procedure
Regards,
Dave
He's probably referring to the procedure described and illustrated in my November '07 article. With a short and fast shot, with the contact lubricated (with Silicone spray or spit), the procedure provides a fairly accurate measure of the "natural pivot length" of the cue. I did some independent squirt and "natural pivot length" measurements, and the results agreed fairly well (see page 3 of TP B.1).Jal said:
Regards,
Dave
Colin Colenso said:
One example: your calculation of swerve includes an estimate of shot speed with values ranging from 1 to 5. The shooter must first estimate which of the five speed ranges applies for the shot (a "feel" estimate) and then execute the shot with that speed (a "feel" execution). So this "systematic" adjustment relies on non-systematic estimate and execution.
pj
chgo
I don't deny there is some feel and inaccuracies involved in estimating speeds, but they can be performed relatively consistantly with a bit of practice and on most occassions, being an entire unit of speed out doesn't create enough of a change to take accuracy outside of the margin of error.Patrick Johnson said:
In banking and diamond systems we can also set speed factors that are useful.
There's a lot of aspects of the game where feel is involved but that doesn't mean that all systematization is superfluous as you make it sound.
I don't expect you to approve of my methods of systematization for BHE as you're not completely familiar with it. I'm just suggesting that I believe this system works and is not a ''ball park" = feel system. It may be ball park, and some of the execution maybe feel based, but the feel is in executing the system rather than in adjusting away from where the system puts you in terms of proper alignment for the shot.
In other systems that have been discussed which I dare not mention for fear of further diverting this thread, little effort is made to explain how the adjustments work. In the past BHE has been regarded as a good system, yet as we've discussed many variables make it complex and in need of adjustments.
What I am attempting to do is to formulate an adjustment system for BHE that is efficient and as accurate as possible. As a player I'm happy with its development and practical application.
Colin