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Re: Altitude Bearing Pressure

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  • jpcannavo
    Tom, Roy The UC18 (and 15 as well). Yeah the bearing arc looks like its no more than 60 degrees. What s interesting is that as far as I know, no one - until
    Message 1 of 10 , Aug 1, 2008
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      Tom, Roy
      The UC18 (and 15 as well).
      Yeah the bearing arc looks like its no more than 60 degrees. What's
      interesting is that as far as I know, no one - until now - has
      commented on this difference in the altitude bearing geometry.
      http://www.cloudynights.com/item.php?item_id=1669
      http://www.cloudynights.com/item.php?item_id=1830
      It is remarkable that the difference in loading Teflon has had that
      dramatic an effect. My own experiments with loading have shown more
      subtle differences in static friction - but I did not get down to the
      low psi range that obtains with a 60 degree arc of Teflon.
      By the way Tom, about how wide...1 inch?
      In terms of a fix, it would seem that Toms approach is the way to go.
      I also wonder if the mating edges of the trunions could be slightly
      beveled so that the EbStr slightly slopes away at the edge. I can't
      imagine that this would then hang-up, especially considering that the
      surface of EbStr has its own surface irregularities with no
      consequent problems. Also, speaking of taping on Teflon - I have to
      share - every one should own some of this stuff. I make great use of
      it - the adhesive doesn't creep/fail - even at higher temp.
      See in Photos under "Joes Stuff"
      http://tech.ph.groups.yahoo.com/group/bigdob/photos/browse/129f
      Website:
      http://www.cshyde.com/Tapes/PTFEtape.htm
      Joe

      --- In bigdob@yahoogroups.com, "Roy Diffrient" <diffrient@...> wrote:
      >
      > Tom,
      >
      > Have you communicated this problem and fix to Kriege? Since he's
      selling
      > them about as fast as they're made, I wonder how receptive he is to
      > significant changes/improvements.
      >
      > Roy
      >
      >
      > ----- Original Message -----
      > From: "Tom Polakis" <tpolakis@...>
      > To: <bigdob@yahoogroups.com>
      > Sent: Wednesday, July 30, 2008 11:42 PM
      > Subject: Re: [bigdob] Altitude Bearing Pressure
      >
      >
      > > ---- Roy Diffrient <diffrient@...> wrote:
      > >> I believe that scope (Obsession compact 18, right?) has long,
      continuous
      > >> Teflon strips to avoid hang-ups on the discontinuity in the
      joint between
      > >> halves of the altitude trunions. So small Teflon pads are not
      really a
      > >> solution_unless_you change to conventional one-piece trunions.
      > >
      > >
      > > Roy,
      > >
      > > Actually, 4 individual pads has turned out to be a very good
      solution,
      > > since there is only one altitude (about 60 degrees) where the pad
      > > encounters the split in the Ebony Star. I went into making the
      change
      > > knowing that I would only be working at that altitude for some
      very small
      > > percentage of the observing time. I expected an
      objectionable "bump" at
      > > that altitude, but how it has really worked out is that the
      telescope is
      > > only a bit more difficult to move for a half degree or so across
      that
      > > split line. And I didn't even taper the Teflon pads.
      > >
      > > So now, instead of a telescope with very poor altitude motion at
      all
      > > elevations, it has moderately poor altitude motion for a half
      degree
      > > around one discrete elevation, and excellent motion otherwise. I
      was
      > > pleasantly surprised by this result.
      > >
      > > Tom
      > >
      > > ------------------------------------
      > >
      > > Yahoo! Groups Links
      > >
      > >
      > >
      > >
      > >
      >
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