Anti skate and tonearm damping query

Mark you said, P=F/A and "The breakdown takes the form of a pressure dependent coefficient of friction; the coefficient decreases with increasing pressure "
Still an example with your choice of tonearm would be helpful.

Axel, the often cited law of friction by G. Amonton (who kind of re-discovered it 2 and a half centuries after its original "inventor" Leonardo) as the main "law" being the skating force in phono playback assumes, that the bearing of the tonearm is not able to *completely support* the resulting force towards the inner groove. This force is a result of the offset of the tonearms "head" and therefor the cartridge and its cantilever. This offset implies a force that would - if not compensated by bearing or lateral balance - swing the tonearm's "offset part" (the "right side" if view from the front towards the cartridge/tonearm head) downwards because it needs to find a stable position in gravity.
Thus resulting in a horizontal force on the inner groove wall.
So far so good.
And I agree with this of course.
This is true for most pivot tonearms.
But not for all I think.
Now what IF the bearing is able to COMPLETELY SUPPORT the resulting force.
It is obvious, that most uni-pivot tonearms and knife edge bearing tonearms (among others) can NOT completely support this force.
However - a rather long effective (12" is fine .... of course 16" would be better) tonearm with resulting LESSER offset and a left side lateral balance can (at least in empirical observations.....) almost (if not 100%) completely support that force, as it is compensated by lateral counterforce.
A completely balanced FR-66s with its lateral balance correctly adjusted and on dead level TT shows no skating force in the 2 zero points of the tangential curve.
2.7 VTF with a stylus even "sharper" than a line contact.
A SME 3012 with bronze knife bearing does show heavy skating even in the 2 zero error points.
Both tonearms adjusted for same tangential curve and running with the same cartridge (FR-7) on the same table.
Maybe this way I can illustrate why i still think, that the model ... maybe .... is a bit more complex as the initial anti-skating model we are used to.

BTW - I vividly remember that the anti-skating devices in former Thorens, some EMT and Dual turntables (among others of west german manufacturers of years gone by) showed at least 2 different anti-skating scales: - one for elliptical stylus, one for conical.........

Ok I can see it now.

The coefficient of friction does indeed reduce with pressure but what we haven't established is that the pressure is a linear function of VTA. For that to be the case contact area would have to be constant and it isn't.

I'm not even going to try to explain why not, I have a reasonable grasp on Hertzian contact theory but not good enough to explain it to you. Google Hertzian contact theory and you might see why.

Mark Kelly

Mark,
+++ The frictional force vector is in the direction of relative motion between the stylus and the vinyl. +++
>>>Yes!

When the stylus is following a groove, this direction is tangent to the groove curvature.
>>>Yes!

When the stylus is not following a groove, this direction is tangent to the scribed arc of the stylus on the vinyl.
>>>Yes!
+++

I completely agree with all the above.

I have no idea where you see a: "false dichotomy"
in my statements of: No friction = no skate force, no groove = no "off-set" in the groove (well there is NONE).

The only other angle is that angle between pin-point stylus to pivot and the pivot to centre of rotation. This angle seeks itself to be closed as soon as a friction force is applied.

If indeed it is what you keep referring to, we have no argument only an issue with terminology.

"Off-set angle" is by definition (in my universe and also at least SME's) the angle the head-shell and thereby the stylus is "off-set" in relation to the tone-arm-wand. This "off-set", (specific to each tone-arm) should produces two null-punkt (0 deg tangent angle) spots on the vinyl after correct alignment.

This tangent (tracing) angle is a constantly changing angle whilst the tone arm moves toward the centre of rotation, or end of record.

I am starting to think you are using "off-set" in place of this variable "tangent trace angle"?!

Sen wat we hav here is se problem mit de "Begriffsbestimmungen", oh mein Gott!?

Failure to communicate?

Axel

Axelwahl

You said no groove = no offset. That's not correct.

The tangent to the arc of the stylus traces on the vinyl does not pass through the tonearm pivot. Therefore there is a separate vector pasing through the same point (the stylus contact point) which does pass though the tonearm pivot. The first vector is the stylus frictional reaction force vector, the second is the tonearm restraining force vector.

The angle between these two vectors is the angle I described as the "true offset" and which we are now going to call something else, hopefully slightly less cumbersome than "the angle between the stylus frictional reaction force vector and the tonearm restraining force vector". As explained above, the fact that the stylus frictional reaction force vector doesn't pass through the pivot is what causes skating. That's all there is. Nothing more, nothing less.

Mark Kelly