Do 45 RPM records need higher anti-skate setting?

We said way back up the thread that groove modulations might in effect alter the coefficient of friction. The only question is and was the magnitude of that effect. I think now it is significant; who could argue with Dr. Alexandrovitch?

But did he really find that "friction remained constant with groove speed"? That speaks to the original question, whether there would be higher skating force at 45 vs 33, and is contrary to our previous conclusion. I can see that the coefficient of friction could go up with decreasing radius, because groove modulations become more tortuous. Have you got an actual copy of this 1961 publication?

I've had conversations with several tone arm manufacturers; they seem to agree that there is no standard for anti-skate forces to be applied to an arm. Put another way they all seem to have different ideas about it.

Thats not surprising to me because we are dealing with varying groove modulations from the first track to the last.

I own two pivot tonearms. Anti-skate is a guess.
To be correct therefore pivoted arms need a different anti skate setting for 33 and 45 RPM records and even different positions along the record.

The best explanation I have personally read that describes this phenomena is from someone that actually tested pivot arms and antiskating. From the Eminent Technology ET2 manual. Page 46

"Antiskating and Frequency Modulation Distortion of Different Tonearm Geometric

Pivoted tonearms are designed so that the head shell holds the cartridge at an “offset angle” with respect to an imaginary line drawn through the tonearm pivot to the stylus tip. The arc traced by the stylus tip extends past the record center and is defined as “overhang”.

This design approach minimizes tracking error. There have been many articles written about the geometry of this design approach. Pivoted arms create several side effects which reduce phono cartridge performance. The first is a skating force which results from two different parts of pivoted arm design.

There is a force component (vector) that is directed toward the center of the record. It results from the stylus drag force vector not falling in line with the pivot point of the arm. This force pulls the tonearm inward and the stylus can be observed as bending outward. This force and the resulting bending can be demonstrated by connecting a rubber band to a pivoted arm around the cartridge body and pulling it straight (away) from the tonearm. Note: the motion of the tonearm is inward and results in bending of the rubber band (cantilever).

If you corrected these forces with an anti-skating mechanism such that the stylus did not bend (you can not really do this because the frictional force and resultant bending varies with groove modulation, stylus shape, tracking force, etc...) there still exists another component of skating.
This second skating force results because of overhang. There are frictional force vectors that result which are not directly ahead of the stylus. The surface of the record is not really moving straight ahead with respect to the stylus tip. As a result, there are force components directed ahead and toward the center of the record. The magnitude of the inward force depends upon the degree of overhang. "

Lewm,
Check out the link to Alexandrovitch and other papers via this link.

He found that with an unmodulated groove, there was no change in friction with radius ie groove speed. With a modulated groove there was an increase in friction, and this increase increased towards the centre, despite, apparently, the reduction in groove speed.

Ct0517,
I don't get the thing in the ET manual regarding the two skating forces. Certainly there is a tiny component of skating force due to the stylus contact point and the cantilever bearing point being in different places, but as far as I am aware that is not a major consideration in terms of the overall picture. But all skating depends on overhang, because it is that which gives rise to the fact that the groove and arm pivot are not in a straight line, thus causing the forces, unlike in the ET which is a linear tracker. If it was set with overhang it would skate too.

John

John, Yes, I just misunderstood the language of your first post on Alexandrovitch. I later figured out what you meant, and there is no disagreement with our earlier conclusion.

I hate to discuss the origin of the skating force, but I love it too. Such is life. My belief is that the prime cause of the skating force is friction of the stylus in the groove coupled with the fact that the cantilever is never tangent to the groove, because of "stylus overhang". "Headshell offset angle" changes the directions of the force vector that results from this. But the net effect is a force that pulls the stylus tip inward along the arc of the tonearm. (Because the tonearm is mechanically stiff and the pivot is anchored, the only way the stylus tip can respond to the forces on it is to "skate" inward on the one permitted path.) This is how I think of it, anyway.

So the idea that a 45 rpm disc cut with greater modulation to also require slightly greater anti-skate sounds like its not that far-fetched.