How to properly set VTF??

Dear Sirspeedy: WElcome a board!!!

+++++ " BTW--If the arm sees the anti-skate as it plays the record,I can't understand why one would not want to adjust downforce with it engaged. " +++++

You are right but there is a little problem: usually the AS value changes a cross the record, so the VTF will change with those AS changes and we need a constant VTF. Now, if we have a constant AS then your idea is not only right but we can work with it.

Regards and enjoy the music.
Raul.

Sirspeedy, unless you have a dynamic load cell at the stylus, you really don't know the 'true' VTF at any given place on the record. If you think that because you reset your VTF to 1.87 that you are getting 1.87 every time, then you are mistaken! The 0.01 variation or precision that you claim is an illusion, since other parameters involved vary more than that. +/- 0.1gm is all that is needed and also to set up with the AS de-activated. Activating the AS will falsify the VTF reading by more than 0.01g due to the horizontal vector force applied. Re-applying the AS after the VTF is set is only approximate anyway and is correct for only 2 spots on the record anyway.
Bob P.

After pondering some of these excellent responses,Bob's really puts the "Kabbash" on anyone using an arm with antiskate.Possibly!

Maybe this is one reason Harry Weissfeld,of VPI does not employ an antiskate setting on his unipivots.

This does seem to lend creedence to the issue of a "tangenital tracking" arm.Like the Air Tangent/Kuzma Airline/or Walker!

In reality I guess the best I can do,in my own set-up,is "guesstimate"!!

However, just to continue the discussion, if we assume that on a given listening session all things being equal (humidity, temp, phase of the moon, etc.) that these variances that Bob mentions across the record will be pretty much the same each time the record is played. (I would hope they are or there is something really wrong with all of our playback equipment.) In this case the VTF of 1.87 is the only parameter we can measure to somewhat predict the behavior of the arm/cartridge across the grooves. Perhaps with some arms and some cartridges it can make a difference. (I admit I haven't experienced it but I don't yet own a cartridge that could respond to that level of adjustment. Mine don't even respond much to VTA changes. :) ) I can't help but draw an analogy to a stock car. The suspension, and thus the load on any tire, is constantly changing all the way around the track but the only way to somehow predict the behavior is to weigh the static load on each tire. Then changes are made during the run to compesate for what is actually happening. We have the advantage in that our "track", the grooves, are much more predictable in that we don't have to worry about what line we trace since there is only one.

Sirspeedy, the reason that AS is not a good idea with uni-pivot arms is that the horizontal vector imposed at the stylus will cause a unipivot to twist and drive the stylus out of azymuth (and also lower the VTF, due to the upward vector imposed by the torque)since there is no bearing in that horizontal plan to counteract that force. My STAX UA7 was a unipivot arm, which had a very elaborate AS (variable across the disc), but I ended up using very little AS, as determined by listening with a test record.
Dan_ed, if every record were recorded at the same level (level and frequency affect the friction which causes the centripedial force, along with the VTF and the 'lack of tangency'), were of the same length and thickness, then yes I would say that extreme accuracy on the VTF would be worth it. However, as you have mentioned, one cannot get 0.01g repeatability reliably from the VTF mechanisms on todays arms. Even those that claim to dial in the 1.87g and play, will tell you that after they carefully and painstakingly set the VTF to 0.01 precision, they then reset the VTF according to ear.
Might as well set the VTF to 1.9g (with less fuss) and then tune the VTF. It is quicker and just as good, depending on your ears, of course.
Bob P.