Re: ATM "Stiction"

[ran@netgate.net]

In <364D7EBC.E1568C8E@fred.net>, on 11/14/98 
   at 07:59 AM, Brad Davy <bdavy@fred.net> said:


>The thrust bearing is a swivel bearing (5 inch
>diameter) from a local hardware store.  While the mount seems to turn
>smoothly, it suffers from "stiction".

I think you're probably kidding yourself about the "turn smoothly":  
you'll probably find unacceptable jumping even after it's moving. Between
the cheap balls and the stamped-steel races,  there are about 43 bazillion
(+- a few jillion) surface irregularities in the system, that will
randomly add and subtract in effect.  Grease will help some,   but I think
you've exceeded the limits of Safe Scrounge,  here.

Why not just replace the Lazy Susan bearing with something like sheets of
Teflon or HDPE?

Or,  here's an idea I haven't tried yet,  but might work:  start with a
metal surface that's "pretty close to" flat and well-polished.  Opposite
that,  mount three Teflon pads.  Run the RA axis at "slewing speed" for a
few days,  periodically repositioning the teflon pads a bit.  This will
tend to fill in surface imperfections in the plate with ground-off bits of
Teflon,  and grind the Teflon bits into a close-enough approximation of
"flat and parallel".

Doing a round with polishing compound first (and replacing the pads) might
make this even better.

Ran


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