For goodness sakes, even 4 years later, kinetic friction is not affected by velocity, because the equation that defines kinetic friction has no term in it for velocity. You can't change the definition or the equation that constitutes the definition, to suit your needs. And the above experiment, using a blank LP, is totally useless.
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Larry. Thx for your input. The paper you cite is interesting. But I guess I pay more attention than you did to the first paragraph, with all its qualifications. It clearly states that the phenomenon exhibited by the experiments done for this paper might be restricted to deformable objects such as a tennis ball. The data and the paper don’t convince me that I am completely wrong. Have you or has anyone noticed an increase in skating force when playing 45 RPM records.? I have not. Now I will go ahead and read the rest of the paper. Perhaps it will change my mind. The question here is whether a diamond stylus tip and a vinyl record groove would behave classically, as described by da Vinci and coulomb, or surprisingly as did the objects used in this particular paper. I obviously enjoy these debates. Which is one reason I am sticking to my guns. For now.
By the way, stiction doesn’t count. We are talking strictly about kinetic friction, not the friction force that pertains when one is setting a stationary object into motion with respect to a surface with which it is in contact. |
Duh! That's what I mean about changes in velocity, which are "accelerations" that generate a force in the horizontal plane. As the stylus bangs into the vinyl while traversing the modulations, the force due to acceleration ADDs to the "normal force" (Fn in the equation), pushing the stylus against the vinyl, thus momentarily increasing friction and therefore the skating force. Like I said, we are not really in disagreement; I am trying to use the correct language to describe what I think is happening. But it's got nothing to do with steady state velocity. Playing a 33 rpm LP generates no less of a steady state skating force than does playing a 45 rpm LP, even though the steady state velocity is greater in the latter case (groove modulation notwithstanding). |
Mijo,
check it out:
F = Fn*mu, where F is the force needed to counter friction between two bodies in motion with respect to each other.
Fn is the normal force ( meaning VTF in this argument).
mu is the coefficient of friction.
Where do you see velocity?
Speed is a scalar quantity; this is about vectors.
Your argument isn’t terribly wrong, except you are resistant to seeing my point that velocity has nothing to do with it; it’s changes in velocity that are causing additional forces. Any change in velocity is an acceleration.
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Mijo, No.
I was going to leave it at that, but let me take your statements in reverse order:
"Tracking angle error has very little to do with it as long as the arm is set up correctly. It is all about friction and offset angle and offset angle is fixed." It's actually about the friction force, we both agree, and about the degree to which the cantilever is not tangent to the groove. A major reason for lack of tangency, for all tonearms that are mounted such that the stylus overhangs the spindle, is headshell offset angle. Again, we agree. But in addition to the headshell offset angle, there is a variable lack of tangency to the groove, created by the tonearm geometry. At the two null points of any typical alignment algorithm, where the cantilever is tangent to the groove (tracking angle error = 0), there is still a skating force due to headshell offset angle. But at all other points on the LP surface, headshell offset angle is not the only cause of lack of tangency. That additional ever changing angle is one reason why the skating force is changing all the time.
"The more tortuous the higher the velocity. The force required to move the stylus back and forth is seen by the system as friction. So, the higher the groove velocity the higher the friction." That's a very appealing concept, and I was sort of thinking that way too, but "velocity" does not appear in the equation for friction. So you and I cannot have it that way. The way I see it now, the tortuosity of the groove results in those mini-acceleration events; the stylus MUST obey the speed of the turntable. No matter how many twists and turns in the groove. Thus, the stylus is experiencing mini-accelerations (acceleration = change in velocity) as it is dragged around the LP at a constant net speed through those zigs and zags of the groove. Acceleration does generate a Force. (Remember, F = ma.) Those small forces being generated, acting through lack of tangency to the groove wall, must be resisted by the cantilever, the cartridge body, and ultimately the stiff tonearm to which it's attached. That contributes to the skating force as well.
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Since kinetic friction (the force of friction between two moving objects) is only a function of the normal force (the force vector that is perpendicular to the contact surfaces of the two objects) and the coeffecient of friction (mu) between the two objects, stylus velocity should in fact have no effect on the magnitude of the skating force. So, for a cartridge and an LP, only the vinyl groove, the shape of the stylus, and the VTF should count. The reason the skating force does change in magnitude across the surface of the LP is due to the ever changing tracking angle error and to groove tortuosity, which forces the stylus to accelerate around the tiny curves in order to hold the speed of its travel constant. These mini-accelerations of the stylus tip, which are happening at all points, cause mini-changes in the force exerted by the tonearm to hold the cartridge in place and corresponding changes in the skating force. That's the way I see it, given that velocity is not a factor in the formula for kinetic friction. |
The TP does have that damping trough near the pivot. Why would that effect the skating force? |
Chakster, probably you shouldn’t disseminate the idea that VTF should equal AS. For two reasons: first, most AS devices are imprecise as to the amount of AS at any particular set point, and second, because many users including me have found that if you can set AS = VTF, you end up with too much AS. Much too much in fact. However I wouldn’t argue that my own findings reveal a universal truth. But read Doug Deacon’s old thread on AS with Triplanar tonearm.
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Miller, Neither I nor cleeds is advocating doing what the op suggests. Let’s keep that in mind.
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Jack, The stylus travels in an arc with the pivot point of the tonearm at its center (not a straight line). Tilting the turntable is about the same as hanging an anti-skate weight on a string, to pull the tonearm toward the spindle (as is done with many tonearms), but it raises other issues of wear and distortion, so I wouldn't advise doing it. (You'd have to tilt the TT very precisely toward the spindle, and you'd be guessing at the resulting anti-skate force.) |
Krell, Over the years there does seem to be general agreement that the "recommended" amount of AS is usually too much for best SQ and even for lowest wear on the cartridge. So, your son's experience is typical. In the good old days, the AS mechanism was sometimes marked with values starting at 0.5 or 1.0. These often were to indicate that if you were tracking at 1.0g, you should use the 1.0 setting on the AS device. Almost always, that is too much AS. |
Cleeds, with all due respect, can you consider the condition where there is no friction between the stylus and the groove? Can you tell me where the skating force would come from if that were the case? Are you capable of thinking this through to its logical conclusion? I really don’t care whether you see the point or not, but I do not like to see incorrect information put forward on the Internet where people read it and believe it.
As I recall, you also claimed that a tonearm without headshell offset would generate no skating force. Anyone who could say that does not understand what’s going on.
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Cleeds, The fact that you cannot see the forest for the trees does not make me wrong. Of course headshell offset angle and other reasons for lack of tangency of the cantilever to the groove are what results in the skating force but there would be no FORCE, with a capital F, without the need to oppose the force of friction between stylus tip and groove. Can you get that?
Have you ever studied Newtonian mechanics? Sit down with a piece of paper and draw some vectors depicting the pull of the stylus that is due to friction in the groove and the need for the tonearm, cartridge, cantilever, and stylus to oppose that force, which is ultimately expressed as the skating force, pulling the cartridge toward the spindle. This happens because the tonearm is stiff and the connection between it and the cartridge is solid. Otherwise the actual force that counteracts friction is toward the rear and inside the arm wand, but the cartridge can’t move that way because of the stiffness of the structure, so another vector is generated which ends up in the skating force.
As I think you have understood, in a straight line tonearm the force of friction is in a straight line with the pivot, if the tonearm is ideal which doesn’t really happen. But in that ideal case there is no skating force because there is no angle between the force of friction in the groove and the force needed to counteract that friction to prevent the cartridge from flying off into space.
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Also centrifugal force, if there were such a thing, has nothing to do with the skating force. |
Genez, Many others have noted, and I agree, that using a groove-less LP may be a good way to demonstrate skating but it is not useful for setting AS, because in real life the cause of the skating force is friction in the groove. Friction on smooth vinyl is different in magnitude. So one should not set anti-skating to oppose skating that is observed on smooth vinyl.
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millercarbon,
How do you set up a tangential tracker with overhang? I would call that condition a "bad job" in setting it up, not an optional method. (I'm sure you would too.) Actually, that's one of the dirty little secrets of tangential trackers; you do have to set it up exactly correctly to get the full benefit. Off-center LPs are impossible to get right.
My only thoughts on reading some of the comments to the effect that this or that tonearm sounded "better" with no added anti-skate is that in every case there was some other force that was approximately cancelling the skating force, either bearing friction or wire drag most likely. And this is fine. Since the skating force is varying in magnitude at every point across the surface of the LP, and since anti-skate devices are relatively primitive, whether magnetic or string and weight type, there is no one single setting of any anti-skate device that works perfectly to cancel the skating force. And most users tend to over-compensate. This is why some report that their SQ got better when they disengaged AS. But the core fact is that every tonearm except a perfectly set-up tangential tonearm with a fixed pivot point will generate a skating force. As others mentioned, Peter Ledermann, who makes a living repairing cartridges, testifies that he sees the negative effects of prolonged exposure to the skating force on cartridges he repairs. My own solution is to set AS very low and not to think much about it after that. |
Cleeds, with no friction of the stylus in the groove, there is no skating force. Head shell offset angle is one cause of lack of tangency to the groove that from a vector force point of view gives rise to the force that pulls the stylus tip toward the spindle. However without friction headshell offset wouldn’t make one single bit of difference, and there would be no skating force. That is the genesis of my remark. And by the way, headshell offset angle is not the only cause of the skating force as far as the geometry goes. Skating force is further augmented by lack of tangency to the groove wall at any point on the LP surface that is not on the two null points of a typical alignment algorithm. Only at those two null points is headshell offset angle the only cause of the skating force. Everywhere else on the LP surface the two geometrical errors that result in lack of tangency are combined.
In addition, you are so so wrong about tone arms that have no head shell offset angle.
There is a lot of wrong information and subjective opinion in the above comments. I hope the OP can sort it out. I would advise the OP to talk to a person that knows this subject, or to do some Internet research looking for the comments of knowledgeable people.
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The FR64S, 66S, and 64fx all do have an anti-skate device built in. So maybe Ikeda was pinching pennies when he designed the lesser models you mention.
I kind of disagree that the tonearm and the cartridge make a “big” difference with respect to the skating force. The skating force is generated by the friction of the stylus in the groove. So I would say the stylus tip shape may make a difference to the amount of skating force. However, if the bearIng is very low in friction, and if the headshell offset angle is designed for any one of the three popular alignment algorithms, then the tonearm really shouldn’t make that much difference. The reason it could make a difference is if the friction at the bearing is on the high side. Thus some of the VPI tonearms that lack an anti-skate device generate an anti-skating force by virtue of the drag caused by the tonearm wires where they exit near the pivot point of the tonearm. I suppose that is true for some other tonearms that just happened to have a lot of bearing friction. I guess I agree then that if you have one of those tonearms which has friction at the pivot due either to bearings or wire drag, either of those factors could lessen the need for a separate anti-skate device. I suppose also VTF can make a difference.
Maybe we’ll find out that the OP is using one of those VPI tonearms, and then we won’t wonder why he does not seem to need a separate anti-skate device. Or maybe we’ll never find out what tonearm and cartridge he uses.
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What tonearm?
what cartridge?
All tonearms that are mounted such that the stylus overhangs the spindle will generate a skating force. It’s the law. Whether you choose to counteract the skating force, or not, is quite another matter.
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