ANTI skate? Then why do they say...

[McIntosh]

to set it so that the arm moves slightly toward the center of the record?

I thought that was the natural tendancy based on the geometry, the arm wants to move to the center.

Wouldn't ANTI skate mean having the arm fight the natural "skate" toward the center and set it to move slightly toward the outside at zero VTF?

Is it that the arm is "pushed" toward the center and you are countering the push by setting it with a slight "inward" movement?

[JBStephens]

The arm doesn't "want" to move in any direction. It is neutral and passive. The reason anti-skate is needed is because the drag of the stylus in the groove is pulling the tonearm at an angle to the pivot because of the bend in the arm or the angle of the headshell. This creates torque at the pivot point, which anti-skate counteracts. That is why straight tonearms don't need anti-skate, and why different stylus shapes require different degrees of compensation, because the drag in the groove is different.

[McIntosh]

your saying a straight tonearm should have zero antiskate?

[JBStephens]

A straight tone arm with a straight head shell won't need anti-skate because you're pulling in a direct line with the pivot point, instead of at an angle to it.

[Publius]

No, a linear tracking arm requires no antiskate. And each different stylus shape implies a different antiskate force. And different amounts of tracking force require different antiskate forces, etc.

It's dependent on a whole slew of factors.

[Manos]

Anti-skating applies an outward force on a pivoting (straight or curved) tone arm to counter the centripetal force pulling the tonearm inward. I understand that the arm should not move inward or outward when set on a smooth, groove-less surface, and when the proper anti-skating force is applied. Unlike pivoting tonearms, linear tracking arms do not need an anti-skating force. Here's where I get fuzzy. The reason the linear tracking arm doesn't need it is because the cartridge is parallel to the arm. With pivoting arms, the cartridge is at an angle to the arm, causing the inward drag. If anyone has a good description of why this occurs, please send it along.

[McIntosh]

Anti-skating applies an outward force on a pivoting (straight or curved) tone arm to counter the centripetal force pulling the tonearm inward. I understand that the arm should not move inward or outward when set on a smooth, groove-less surface, and when the proper anti-skating force is applied.

This quote is straight out of the manual for a Schroeder arm. This suggests an inward force.

adjust antiskating until the arm/cartridge combo wanders slowly towards the center of the record.

[Manos]

This quote is straight out of the manual for a Schroeder arm. This suggests an inward force.
Not exactly. It recommends applying an outward force to counter most of the inward force. Without anti-skating, the arm would slide inward rather quickly.

[McIntosh]

Now I am confused.

How is having the arm moving toward the center an outward force?

[Manos]

Now I am confused.

How is having the arm moving toward the center an outward force?
The arm moves toward the center due to the centripetal force applied by the groove friction below. The anti-skating force counters this inward drag with some outward drag to cancel it.

[MikeyH]

to set it so that the arm moves slightly toward the center of the record?




By 'move' I can see you're trying to use a blank test record, or a blank part of a normal disc. This doesn't make for a good setting, to counteract the sideforce generated when playing a record. (the reason for this inaccuracy is that the sideforce is generated by the drag of the groove on the stylus; you can see that the drag of a groove (stylus in the groove) is quite different to the drag of the stylus point sitting on a flat disc surface. Quite a bit less than half the groove drag)

Using a tracking test record gives better results; and the really advanced set it by ear on 'difficult' recordings.

[JBStephens]

The arm moves toward the center due to the centripetal force applied by the groove friction below. The anti-skating force counters this inward drag with some outward drag to cancel it.

If you mean "centrifugal" force, there is none. Centrifugal force applies only to rotating bodies, and then, centrifugal force will fling an obect outward from the center of rotation.

To understand the concept of anti-skate, imagine a spool of thread on a spindle, with the thread coming off the right side of the spool. That's your tone arm. Now pull on the thread, and the spool will rotate. The same thing happens when you play a record. It's applying a rotation to the pivot because of the bend in the arm. The pull is not tangent to the pivot. But, if the thread is tied to the MIDDLE of the spool, and you pull on the thread, the spool will not rotate. That's a straight arm. No rotation. No anti-skate needed.

Hope that helps de-mystify things somewhat.

[Manos]

If you mean "centrifugal" force, there is none. Centrifugal force applies only to rotating bodies, and then, centrifugal force will fling an obect outward from the center of rotation.
I agree. "Centripetal" force isn't really a single force pulling directly inward, but the sum of forces acting on an angled stylus resulting in an inward pull.

To understand the concept of anti-skate, imagine a spool of thread on a spindle, with the thread coming off the right side of the spool. That's your tone arm. Now pull on the thread, and the spool will rotate. The same thing happens when you play a record. It's applying a rotation to the pivot because of the bend in the arm. The pull is not tangent to the pivot. But, if the thread is tied to the MIDDLE of the spool, and you pull on the thread, the spool will not rotate. That's a straight arm. No rotation. No anti-skate needed.

Hope that helps de-mystify things somewhat.
That's a good explanation. But let's clarify what you mean by a "straight" tone arm. Many tone arms are "straight," as opposed to curved. You are referring to an arm where the axis, or center line, of the cartridge is parallel to the axis of the arm. Only linear tracking arms meet this condition.

[JBStephens]

I agree. "Centripetal" force isn't really a single force pulling directly inward, but the sum of forces acting on an angled stylus resulting in an inward pull.


That's a good explanation. But let's clarify what you mean by a "straight" tone arm. Many tone arms are "straight," as opposed to curved. You are referring to an arm where the axis, or center line, of the cartridge is parallel to the axis of the arm. Only linear tracking arms meet this condition.


Um... if you'd be kind enough to go back about 5 posts to where I said "A straight tone arm with a straight head shell..." :p

A linear tracking arm is what I used when I built the cylinder player.

[Publius]

Actually, a lot of DJing turntables use straight tonearms, straight headshells, but are pivoting instead of tangential. They have *obscene* tracking angle error - 10-20 degrees or more. But the skating force is still lower with them - that's actually one of their biggest selling points; it's much easier to backspin the record without skipping, compared to an angled headshell.

[Fedot L]

Here are some specialists’ explanations which I hope can help the participants on the subject matter:
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ANTI-SKATE BIAS
In discussing any pivoted tonearm design some clarification on anti-skating bias is warranted. Skating force is generated during record play by the stylus of a cartridge mounted in any pivoted tonearm. Frictional force, (stylus drag force, “F”), is generated in the direction of groove-to-stylus motion, at a tangent to the record groove at the tonearm null points. The direction of this force vector is offset from the tonearm pivot by the headshell angle (“theta”) and can therefore be resolved into 2 perpendicular force components, one of tension along the cantilever centerline and one of skating perpendicular to the cantilever centerline, forcing the headshell toward the center of the record. The coefficient of friction between the record and stylus, “u”, multiplied by the tracking force, “T”, and sine theta, will give the magnitude: F = (u x T x sine theta). Assuming u = .13, for the Vector tonearm at a 2 gram tracking force F = .13 x 2 grams x .391 = .10 grams. Anyone who has experienced the large difference .10 grams makes in tracking force and cantilever compression would agree that this amount of sidewall force could destroy records and reduce sound quality if not negated.
http://www.basisaudio.com/refs/vector_whitepaper.htm
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With the cartridge oriented correctly in relation to the groove, the latter moving past the stylus strictly in line with the pickup head's axis, it follows that any forward frictional drag exerted on the stylus by the groove does not simply pull directly and neutrally on the pivot, but when projected back, is seen to apply a clockwise turning force about the pivot due to the offset geometry. The net result is that whenever the stylus is in the groove of rotating record the pickup is subjected to an additional inward force. To overcome this, arms are fitted with devices known as bias compensators or anti-skating devices. The optimum bias compensation force is dependent on tracking, force and stylus profile, and is best set empirically using a test record like this one. 'VTA', or Vertical Tracking Angle, strictly refers to the angle of the vertical motion path of the cutting stylus used to make the record. For many years this has been standardised at 20° ahead of true vertical. It follows that the replay stylus should move at this same angle when deflected vertically, and that its tracking 'edges' should engage with the groove accordingly, especially with the more advanced 'long contact area' stylus types. In theory, this condition should be achieved when the stylus is loaded by the maker's recommended tracking force, and the arm and cartridge body lie parallel to the record surface, as in Fig 6. In practice a small deviation from this position may be found to give the best results. Most arms have provision for height adjustment at the pivot end.
http://www.smartdev.com/LT/Align.htm
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And two graphs: