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> o far I only managed to measure the index error
> after my visit to Freiberg. It is -0.6' now.
> (Before it was 0 consistently from October 2004 till
> my visit to Freiberg).
> Another thing I notice is that the screw rotates more
> smoothly after the Freiberg adjustment.
>
> But I am puzzled with this whole business.

Alex

Had a perhaps similar experience today.  A few days ago a laid out a 100 yd
mark from a black light post, and put 1/4" 1/8" and 1/16" pieces of white
tape around it horizontally.  It was a test range for finding a parallax
angle at 100 yards for using the sextant as a range finder.  I tripod
mounted the sextant and took 10 clockwise and 10 anti-clockwise
measurements.  STDEV was approx. .06 minutes.  The angles measured were very
close to those arrived at with trig from measurements taken of the sextant
mirror distances.

Repeated the experiment today and STDEVs were in the same ballpark, but the
angle off the arc had grown by a full minute.  In essence (working
backwards), the difference between the line of sight through the scope and
axis of the index mirror was 1 inch more than reality based on todays
angles.  I then did an IE check with the SUN, and overnight my IC went from
-.5' to +.5'.

I called the always helpful folks at Celestaire.  Ken first asked me if the
arc was clean, to which I replied, "yes."  Then he walked me through a few
areas that might present problems.  I checked them out after the
conversation, and everything seemed OK, so double checked the gear
cleanliness.

Despite using the supplied brush on a regular basis, I could see a brass
build up in frequently used areas with the naked eye, and used a loupe to
examine the arc teeth. They could be cleaner. I used a new toothbrush (as
toothpaste has abrasives) to clean the arc until the brass was gone and they
looked clean under the loupe. Then I lubricated the arc and worm gear.  I
still had a little tactile bump when the drum was rotated through 60 minutes
which I had mentioned to Ken, but it seemed to move locations about 15-20
minutes with each rotation as before.  Then I looked at the worm gear with
the loupe.  There was a little smidge of something animal, vegetable, or
mineral that was lodged in the worm-gear (and must have sneaked in there
between bringing the sextant in last night, putting it in the box, and
taking it outside today). It was barely visible to the naked eye when I knew
where to look.

I cleaned the worm gear and went back out to my parallax test range.  Bingo,
target numbers were the same as yesterday, and IC was back to -.5' from the
earlier shift to +.5'.

Might be worth checking out?

Bill

   

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