Anti skate and tonearm damping query

Mark,
am I having a different understanding of what is off-set?

It may explain perhaps some crossed wire...

"Off-set" in my vocab is the angle that a head-shell / cart /cantilever is mounted out of the true / straight line with the tone-arm-wand i.e. 0 deg = no off-set.

As to the various measured forces caused by friction between various materials I have no issue with at all.
In fact, and often, the faster the speed the LESS the friction force e.g. when an object starting to plain on water, rather then being dragged through it is some extreme case in point.

If a tiny tip of a stylus is 'dragged' over smooth vinyl, I can see that no measurable difference in friction force would be the case.
However, no friction force *NO* skate force!

It is this friction that wants to pull the stylus tip with it. Since it can't, due to the arm pivot holding it back, it will do the next best thing and pull the arm in line with the center of rotation. This would also be the shortes distance from pivot to center of rotation, right?

Like a pendulum being pulled (eventually) to the shortest distance from pivot to the center of gravity.

No gravity force, the pendulum will remain where ever is happens to be.

Axel

Mark, my rudimentary understandig says line contact has less force on the groove wall so shouldnt less force lead to lower friction and hence lower skate force, but I cant reconcile this with your Amonton law breakdown stating lower pressure implies higher friction, although wont some of the breakdown be ameliorated by the cantilever making the diamond less hard compared to the vinyl?

Axelwahl

I think I have confused you by trying to simplify things. The angle I referred to as the true offset is the angle between the groove tangent and the line between the stylus and pivot. The frictional force acts along the tangent so this is the angle between the frictional force vector and the restraining force vector. The true offset angle varies with groove radius for ordinary pivoted arms and the offset angle of the arm is an approximate average of the true offset angles.

I can see how this is confusing and I should probably have used a different term.

Perrew

You are confusing force and pressure. The force is set by the VTF and the groove angle, so the sum of the forces on the sidewall is SQRT 2 times the VTF (for 90 degree groove). The pressure is this divided by the contact area. Larger contact area = lower pressure for a given VTF.

Mark Kelly

Mark, so increasing the VTF would increase the pressure and the skate force would decrease, all else equal? Wouldnt this imply that high VTF means anti-skate can be ignored?

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