Anti skate and tonearm damping query

Mark,
ja now fine, and so we have even more discrepancies since I, for the sake of TRUE simplification, been talking over and again about BLANK vinyl, and the stylus point riding on this smooth surface --- AND THEREBY taking any of this groove tangent stuff OUT OF THE EQUATION.

There IS a skate force WITHOUT any groove! Therefore NO tangent, what so ever comes into play as I tried real hard to get across.

Taking things into the groove, with all this stuff Perrew is on about is no good, if the basics are not cleared up, yes?

So, again, NO friction force, NO skate force, period.

Tangent has NOTHING to do with it at this point, *if we are NOT in any groove*!
As such all this talk about tangent, or off-set, etc. only serves to cloud the basics of the skate force issue --- unless you are much more deeply into the details then at this point was my understanding.

As such, and going back to the SIMPLE, *no groove*, model Dertonarm is NOT right in assuming a zero skate force at a 0 groove tangent angle.
I can prove that, as soon as there is friction, there is a skate force.
His (Dertonarm's) point is such only of any relevance, if at 0 tangent groove angle -- and as he assumes --- there be less friction force than at any other angle.
If this be so in the first place (and I have no explanation why it should be so!), it be so minute a difference, as to have no measurable effect.

Therefore off-set is as little part of the PRACTICAL equation as is Over-Hang. If one groove side is traced a micro-millimetre later (or earlier) then the other --- what be the increased friction due to that?
None! for a spherical stylus, and none for most any other stylus as well, even it the sides be a sharp as it gets.

It will make a mess of the signal, oh yes, but that is another discussion all together i.e. correct cart alignment.

Axel

Perrew

I cannot see how you can get to that conclusion.

Axelwahl

I love how you can take a simplification and twist it until it becomes a complexity. Your jump from "no groove" to "no tangent" is unjustified.

The frictional force vector is in the direction of relative motion between the stylus and the vinyl. When the stylus is following a groove, this direction is tangent to the groove curvature. When the stylus is not following a groove, this direction is tangent to the scribed arc of the stylus on the vinyl.

The rest of your post rests on this false dichotomy so it also falls (except for the bit about our befuddled friend DT not knowing what he's talking about. That I agree with)

Mark Kelly

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