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on 8/30/04 1:19 PM, Renee Mattie at reneemattie@HOTMAIL.COM wrote:

> I have just bought myself a Freiberger drum sextant,
> used, made in 1976. I am happy with its overall condition.
> It works well.  Other than a few scratches in the middle
> of the frame, nothing looks terribly worn. I want to start
> out on the right foot with it, of course.
>
> If anyone has any tips or warnings to offer on disassembling
> and reassembling this sextant, I'd really appreciate learning
> more about it.
>
> Why would I want to do this?  There is a small amount of corrosion
> on some of the screws.  I think the thing to do is to remove
> the scope, mirror, and shade assemblies, wash the sextant
> to remove particles, the completely disassemble it for a
> more thorough cleaning, coat the non-moving parts
> (including screw threads) before reassembly to prevent
> corrosion, and lubricate the moving parts.
>
> So far, I have only been bold enough to remove the handle
> by unscrewing the upper leg stub and the large lower
> screw.  I see a waxy substance in the screw holes.
> I have no way of knowing if it was ORIGINALLY waxy,
> or if this is a grease that has gone waxy with age.
> In this forum, I have seen the following recommended
> for protection from galvanic corrosion:
> * Never-Seize
> * Lanocote
> * TefGel
> * Krytox with corrosion inhibitors(which Jared Sherman
> frequently recommends highly for a number of reasons)
>
> I don't see any recommendations for:
> * Hydrophobic dry coatings (like sailkote, which contains Krytox)
> and I wonder why.  Jared Sherman is of the opinion that these
> spray-on coatings just don't last very long.
>
> I am eager to take the sextant apart, but I want to be
> prudent.  I understand how to create a proper workspace,
> label and lay out each and every part, put screws back into
> same holes they come from, and take pictures along the way
> to remind me what it ought to look like when I'm done.
>
> It's just that I've never done this before, and there is no
> shop manual.  It looks like a straightforward job, but I
> really would appreciate hearing more from anyone who can
> give me a heads-up on any stupid thing a beginner is likely
> to do wrong.
>
> And I am up in the air about what to put on the screws before
> I put them back in.
>
> Thanks for your help!
>
> Renee
>
Renee,

Under the heading of not doing anything dumb, I would recommend not doing
two things.  Do not take the arm out of the frame, or move any screws
associated with this area other than removing a cover to apply lubricant.
Final assembly is done in the factory with the sextant on a testing machine.
Set screws are adjusted to center the pivot exactly during the test.  The
other area which I would not disturb is the worm gear, other than to clean
and lubricate.  I have always found that to disassemble and re-assemble any
kind of gearing invites the prospect of mismatching of teeth or axes which
results in high and low spots of tactile feedback, new wear patterns, or
other mysterious results that just don't seem right.

Ken Gebhart

   

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