Anti skate and tonearm damping query

Axelwahl

Go back and read my post 15 above this one.

Mark Kelly

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?