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    Re: SNO sextants
    From: Joel Jacobs
    Date: 2004 Nov 11, 11:45 +0000
    Ken Gebhart wrote a while back that it was not wise to disassemble a tangent screw. He made the point that non-adjustable errors were the result of its factory positioning, and if its position changed, the error would change. If I misquoted him, I appologize, but I find that postition correct, but overstated. Whatever error that would be introduced would not be great and could be determined by comparing sights before and after. Furthermore, it is a known problem with the Freiberger and other sextants with an enclosed tangent screw, that they freeze. IMO, its better to have a working sextant than no sextant, so taking it apart when necessary makes sense.
    I've done it and don't find it difficult. You also can mark the tangents screw's position before dissasembly. You may be off a tooth, but I'm prepared to accept that.
    Joel Jacobs
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    -------------- Original message from Alexandre Eremenko <eremenko{at}MATH.PURDUE.EDU>: --------------

    > Jared
    > mentioned the grease and Freiberger sextants,
    > so I want to ask those who have experience with
    > Freibergers and SNO-Ts:
    > Do you ever disassemble the drum?
    > Does it need inside cleaning?
    > A strange-looking wrench needed for this comes as a standard
    > accessory.
    > I am somewhat afraid to do this: the instruction manual
    > says: never disassemble the sextant.
    > But it also mentions periodic maintenance is a special shop:-)
    > In general, I don't see what is the purpose of this
    > enclosed drum. If it is to keep the worm assembly clean,
    > I would rather make is visible and accessible for
    > cleaning, as in most sextants.
    > By! the way, SNO-T comes with a bottle of oil and the manual
    > gives the precise description of this oil (some
    > Soviet standard) and also says:
    > a substitute can be "Aeroshell Fluid 12"
    > manufactured by Shell.
    > Does anyone know what is this?
    > > suppose that if the standard Soviet sextants
    > > were assembled with a grease
    > > that would not freeze up in Arctic use,
    > > that grease might be unsuitable in
    > > the tropics, i.e. migrating too much,
    > > so something as slight as the grease
    > > might be changed.
    > The manual describing my "Tropical" sextant says explicitly that
    > it is suitable for "unlimited region of navigation".
    > > Maybe the color of the
    > > sextant?
    > Maybe. All SNO-T I've seen have the same color: grey.
    > (And now we know that the T stands for "tropical").
    &g! t; Unlike SMO-M which according to Joel comes in variety
    > of colors (I see black, green, brown and grey on maurnavy site).
    > Alex.
    > On Wed, 10 Nov 2004, Jared Sherman wrote:
    > > curious to find out what the
    > > Soviet Navy considered "tropical".
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