Bridge Pivot Point

Tennesseejoe

Tennesseejoe

AzB Silver Member
Silver Member
If my bridge length is 8 inches and my shaft pivot point is 8 inches ...how could a low deflection cue help aiming with English?

As a comparison, I use an OB Classic with about a 12 inch pivot point and my bridge length is about 12 inches when playing 9 ball on a 9 foot table. However when I play bar box 8 ball I use an 8 inch bridge to get more precise position.
 
deraltefritz

deraltefritz

AzB Silver Member
Silver Member
If your bridge length is equal to your shaft's pivot point, it will allow you to aim center ball and then pivot the cue (back hand English, BHE, see Dr. Dave's resources) to the desired left/right tip offset. The deflection or squirt will be compensated for any amount of side spin, and the cue-ball will go into the direction of your initial aim before pivoting.

!BUT! that is only true for medium or hard paced shots up to a certain cb-ob distance.

If you play the shot slower, or the distance between cue ball and object ball is large, the cue ball will swerve (curve) because the cue always strikes a little downwards w.r.t. the slate. A baby-masse effect if you will. If your bridging close to a rail, this effect is increased. It is also highly dependent on the friction of the cloth, and (when the swerve starts/ends) very much on the speed of the shot. So in general, swerve is the harder part to master.

In this case, you may have compensated the deflection/squirt part, but the swerve will deviate the cue ball towards the side of the spin used. A little overcompensation with just a hair of side spin, a significant amount of overcompensation with maximum side spin.

So while bridging at the shaft's pivot point makes it easier to compensate deflection for harder shots, in general your choices are:
- when using BHE only: use different bridge lengths depending on the pace and/or distance of the shot. Shorter bridge length for harder shots (mainly compensating squirt), longer for long distance or slower shots.
- apply a combination of BHE and front-hand english (FHE), also varying the ratio of both depending on pace and distance
- aim thicker/thinner when sticking to a particular bridge length and back hand english exclusively. This is hard as the exact amount of aim compensation varies with cb-ob distance.
- establish all of this by feel, duh ;-)

If you lower your bridge length on a 7ft table, you will in general overcompensate your side spin shots. So either
- use more FHE
- aim thicker (outside english) or thinner (inside english)
- use a traditional maple shaft (or a house cue) with more squirt/deflection
 
Last edited:
Patrick Johnson

Patrick Johnson

Fish of the Day
Silver Member
deraltefritz said:
If your bridge length is equal to your shaft's pivot point, it will allow you to aim center ball and then pivot the cue (back hand English, BHE, see Dr. Dave's resources) to the desired left/right tip offset. The deflection or squirt will be compensated for any amount of side spin, and the cue-ball will go into the direction of your initial aim before pivoting.

!BUT! that is only true for medium or hard paced shots up to a certain cb-ob distance.

If you play the shot slower, or the distance between cue ball and object ball is large, the cue ball will swerve (curve) because the cue always strikes a little downwards w.r.t. the slate. A baby-masse effect if you will. If your bridging close to a rail, this effect is increased. It is also highly dependent on the friction of the cloth, and (when the swerve starts/ends) very much on the speed of the shot. So in general, swerve is the harder part to master.

In this case, you may have compensated the deflection/squirt part, but the swerve will deviate the cue ball towards the side of the spin used. A little overcompensation with just a hair of side spin, a significant amount of overcompensation with maximum side spin.

So while bridging at the shaft's pivot point makes it easier to compensate deflection for harder shots, in general your choices are:
- when using BHE only: use different bridge lengths depending on the pace and/or distance of the shot. Shorter bridge length for harder shots (mainly compensating squirt), longer for long distance or slower shots.
- apply a combination of BHE and front-hand english (FHE), also varying the ratio of both depending on pace and distance
- aim thicker/thinner when sticking to a particular bridge length and back hand english exclusively. This is hard as the exact amount of aim compensation varies with cb-ob distance.
- establish all of this by feel, duh ;-)

If you lower your bridge length on a 7ft table, you will in general overcompensate your side spin shots. So either
- use more FHE
- aim thicker (outside english) or thinner (inside english)
- use a traditional maple shaft (or a house cue) with more squirt/deflection
Click to expand...
:thumbup2:

Well done.

pj
chgo
 
Tennesseejoe

Tennesseejoe

AzB Silver Member
Silver Member
Thanks for the excellent reply.

Now for one more question...Dr. Dave states that a cue ball will deflect to the opposite side of which English is applied until you reach the pivot point. When you reach the pivot point, deflection stops. If you go further past the pivot point, the cue ball will deflect in the opposite direction. I find this hard to believe or did I interpret this incorrectly?
 
Patrick Johnson

Patrick Johnson

Fish of the Day
Silver Member
Tennesseejoe said:
Thanks for the excellent reply.

Now for one more question...Dr. Dave states that a cue ball will deflect to the opposite side of which English is applied until you reach the pivot point. When you reach the pivot point, deflection stops. If you go further past the pivot point, the cue ball will deflect in the opposite direction. I find this hard to believe or did I interpret this incorrectly?
Click to expand...
You must be misinterpreting - or I just don't understand what you're trying to say.

What does "until you reach the pivot point" mean?

Deflection doesn't stop - you adjust your aim to compensate for it. The pivot point (different for every cue) is where you can pivot your cue to create the correct compensating angle for whatever amount of spin you use (ignoring swerve).

pj
chgo
 
Tennesseejoe

Tennesseejoe

AzB Silver Member
Silver Member
Patrick, thanks for your response. This is the article that I think I am misreading.

This from Dr Dave's site and refers to Diagram 3 which I could not copy to this post. I am referencing Case "C".

David Alciatore, PhD (“Dr. Dave”) ILLUSTRATED PRINCIPLES
“Squirt – Part IV: BHE, FHE, and pivot-length calibration”

In Diagram 3, three cases are shown: “A, “B,” and “C.” Case “A” corresponds to a bridge distance shorter than the natural pivot length. The pivot angle of the cue is too large, as compared to the squirt angle, and the CB goes left of the centerline as shown in the diagram, causing the OB to go right of the centerline. In this case you need to move your bridge farther away from the CB and try again. Each time you move your bridge, mark the new location on top of the shaft with a small piece of tape or Post-It note. Case “B” corresponds to the bridge distance being exactly equal to the natural pivot length of the cue. In this case, the pivot angle exactly cancels the squirt angle, and the CB and OB both head along the centerline, ignoring throw for now (see the next paragraph). So if the OB heads straight, then the bridge distance (or grip distance) is what you want to use when applying the BHE (or FHE) method. Case “C” corresponds to a bridge distance longer than the natural pivot length. The pivot angle of the cue is too small, as compared to the squirt angle, and the CB goes right of the centerline, causing the OB to go left of the centerline. In this case you need to move your bridge closer the CB and try again. If you keep adjusting your bridge location, eventually you’ll see case “B” and you will have found the natural pivot length for your cue
 
Patrick Johnson

Patrick Johnson

Fish of the Day
Silver Member
Tennesseejoe said:
Patrick, thanks for your response. This is the article that I think I am misreading.
[snip]
Click to expand...
That's Dave's description of how to find your cue's pivot point so you can put your bridge there to "automatically" adjust your aim for squirt using "backhand" english (BHE)*. It says that if you use BHE with your bridge in front of your shaft's pivot point you'll overcompensate for squirt and with your bridge behind your shaft's pivot point you'll undercompensate.

Hope that helps.

pj
chgo

*Backhand english (BHE) means applying side spin by starting at center ball and moving just your backhand sideways (pivoting your stick at your stationary bridge) to apply the amount of spin you want. If your bridge is exactly at your shaft's "pivot point", stroking the cue at its adjusted angle will exactly compensate for the amount of squirt for that much spin (ignoring swerve).
 
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deraltefritz

deraltefritz

AzB Silver Member
Silver Member
Tennesseejoe said:
Thanks for the excellent reply.

Now for one more question...Dr. Dave states that a cue ball will deflect to the opposite side of which English is applied until you reach the pivot point. When you reach the pivot point, deflection stops. If you go further past the pivot point, the cue ball will deflect in the opposite direction. I find this hard to believe or did I interpret this incorrectly?
Click to expand...

Maybe you just misinterpret the second "opposite".
The cue ball will always deflect, as Patrick says, to the opposite side of the tip position. But always with respect to the line of the cue. If you adjust that line by pivoting at a certain point on the cue, you can make the cue ball go along the aiming line.

Imagine you pivot the cue around a point 10 feet behind you (front hand English to the extreme). This approximates basically a parallel shift of the cue. You will have under-compensated the deflection hugely. Now imagine pivoting around the tip (bridge length of 0). Then you can easily see how you would over-compensate dramatically.
 
Tennesseejoe

Tennesseejoe

AzB Silver Member
Silver Member
Finally I understand. Thanks so much guys, this really helps. I guess I have had a mental block thinking that deflection was reduced to "O" and then turned negative.

You guys are the best....thanks again.
 
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