NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: A-12 sextant question
From: Jean-Philippe Planas
Date: 2006 Oct 15, 14:28 -0700
From: Jean-Philippe Planas
Date: 2006 Oct 15, 14:28 -0700
Just rotate the drum until the arm reaches its stop either at 0° or 105°. When the stop is reached, insist to go further by still rotating the drum. Then the rachet should operate resulting in clutching out the gears and lifting the axel. Go on until the axel positioning pin is abeam the drum groove.
But pay attention with those old instruments. The rachet might be stuck or inoperant resulting in a possible gear damage.
The fact that the axel pin is in such a position means that the arm has already been rotated to its stop while the operator was rotating the drum further on.
Also note that if the gears are already damaged (tooth missing) either at 0° or 105°, then the system might not operate and/or you might induce more damage on the gears in this sector.
If your instrument is working well besides this condition (drum position), don't be too eager to apply the above procedure as you don't
know the history and the internal condition of the instrument. Could create more harm than good.
Good luck.
JPP
"James R. Van Zandt" <jrvz@comcast.net> wrote:
As I have mentioned, I have recently bought an A-12 bubble sextant. I
have since refilled the bubble chamber with xylene and made a sun
shot.
However, I have a question: The sextant came with three plastic drums
to record measurements. How do I take off a drum?
According to the user manual, it should be simple:
"Lift the drum straight off the Sextant. It will be noted that the
drum is fitted to a flange which has three studs. Two of these studs
are small and long enough to extend through the operating drum. The
remaining stud is shorter and larger so that it is impossible to put
the drum on in the wrong position"
However, I think my sextant has been assembled incorrectly. I've
posted a picture here: http://jrv.oddones.org/A-12-drum.jpg. In
addition to studs mentioned above, the drum has a slot and the shaft
has a key. However, on my sextant, the key and slot are almost 180
degrees out of alignment. The drum cannot be pulled directly out
because of the key, and cannot be rotated because of the studs.
I can see two possible ways to proceed. The studs have slots,
suggesting I might remove them with a screwdriver. I actually tried
that, but they didn't budge. The other way would be to remove the
"spring lock" from the other end of the shaft. I'm not sure that
would accomplish anything - the manual tells me to remove the spring
lock only after I "remove the three screws from the countershaft and
trigger bracket assembly". However, the drum is covering those three
screws.
Any suggestions would be appreciated.
- Jim Van Zandt
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