Re: [ATM] Use of bearings in (static) mirror cells

["Don Clement" <clement.focuser@verizon.net>]

>
> If anyone has access to a "higher quality" audio
> turntable" (PRE-CD ERA) you can get an idea of the
> design where the GYMBALS and counterweight are
> adjustable for fine tuning the effect on the glass.
> Imagine the GYMBALS as part of the cell and the tone
> arm the link to the mirror.

A Long Time Ago in a Galaxy Far, Far Away in the Pre-CD analog epoch, I
experimented with replacing the "gimbals" in "high quality" counterweighted
tone arms with flexural pivots. Flexural pivots eliminated all stiction with
tone arm movement and were a great improvement to performance.  Much better
than the knife edge bearings used in SME tone arms. Also a spring bias could
be imparted using  flexural pivots the same way that springs were used on
the  ESL tone arms. Another compliant mechanism from analog epoch was the
legendary Decca cartridges that used a single cantilevered flexure
positioned between fixed coils to coax the subtlest nuances from vinyl. See
http://www.tnt-audio.com/sorgenti/deccalondon_e.html



A few years ago when the supports for the Palomar 200" mirror had to be
rebuilt it was rumored that flexure pivots had been considered to replace
the grease-lubricated ball bearings races used in the original mechanisms. I
am not sure what the reason was for flexure pivot consideration, but flexure
pivots would have eliminated one reason for future rebuilds because no
lubrication is required.  Mirror cells for large portable Dobs are located
near the ground and exposed to grit and dirt contamination,  (and cooling
fans).  I would think that flexure pivots would be highly desirable because
of complete immunity to grit and dirt contamination and no need for
lubrication. Immagine that soft Teflon  bearing embedded with a layer of
abrasive grit  pitting the ball bearing support.



Don Clement

Running springs, California

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