Philosophy: Bearing vs. Unipivot

I want to thank you all, and to Doug have just a couple of comments for clarification. I understand that one part moving on the point of another constitutes a bearing. Perhaps I should have specifically named ball bearings, but then folks may have thought that I didn't know that knife edges were also bearings. Having a stylus captured between both vertical and horizontal ball bearings means to me that, apart from micro movement from bearing slop, the stylus will maintain azimuth, and will not tip to the right or left in the groove. That right or left tip is what I meant by relative movement. The same thing can be said for the old Rabco servo driven arm; it was always in front or behind the angle the groove was cut at. With this relative motion is a loss of information from the groove.
I know that there are many unipivot tonearms that are astonishing, so obviously these problems have been scotched, if not killed. Like you, and architect Mies said, God is in the details.

Benjysch, thanks for clarifying. Parts of my post addressed azimuth instability, so hopefully not a total waste. Some unipivots address this successfully, others not so much.

I'm no van der Rohe (thanks for the comparison) but I am a stickler for details in technical discussions. I draft and negotiate legal contracts for a technically oriented multi-national, where nerdliness is next to godliness!

P.S. You gotta love that Rabco. A fun design, even if it never achieved groove tangency except by random chance. I still have my ST-7 and it works perfec... umm, as well as it ever did.

I owned a Rabco for years. I set it up with an opamp to sense the feeler contacts to reduce noise (I got tired of the feelers not making good contact, which would result in the arm lifting off at random points on the LP...) At the same time I also integrated the output response so it would ramp up slowly and ramp down slowly.

The result is that the motor was always turning. This reduced the "error" (BTW Rabcos have **way** less error than radial tracking arms) by about 1.5 orders of magnitude- the arm would find the horizontal cutting speed of the LP and track with it. It was really easy to do.

Ralph, I respect your broad knowledge so could you explain "horizontal cutting speed"?

Obviously the rotational speed of the platter in cutting (and playback) should be constant. But groove spacing is not (a challenge for tangental arms). As I understand the process one task in mastering is to monitor loudness and frequency and adjust spacing since the groove dimension (width) is not constant. That would seem to complicate things.

If I have mis-information, kindly explain.

Groove spacing is in fact what I mean when speaking of horizontal speed. Many records are in fact cut with a constant groove spacing but most are not. At any rate, the arm can be made to track the variable groove spacing with no worries.