Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Site details
    From: Gary LaPook
    Date: 2008 Nov 30, 04:11 -0800

    Gary adds:
    When reassembling the A-10 the easiest way to align the index prism is
    to use the sextant like a normal marine sextant. Set the counter to
    zero. Install the index prism and the fixed prism but don't tighten up
    the screw holding the index prism shaft, just hold the prism in the
    frame with your finger. Don't install the plates that close the inside
    of the the A-10 frame as they limit your ability to push the index
    out of engagement with the worm.
    Go outside and sight on a clear object in the distance, the farther
    better, by looking around the left edge of the fixed prism. Then move
    the index prism up or down by moving it slightly to the left to
    disengage it from the worm so that it can be moved up or down. Let it
    drop into the worm when you have the same object lined up in the prism
    with the object as viewed around the lefthand edge of the fixed prism,
    then tighten up the screw to hold the index shaft in.
    When reassembling the index prism into the frame put grease not oil on
    the tapered shaft because the tapered shaft applies a great deal of
    pressure on the mating surface and oil is not strong enough to supply
    enough lubrication. If you use oil you will end up with a horrendous
    amount of backlash, say about a 30' difference when you bring a star
    or down..
    The trickiest thing about installing the index prism is installing the
    spring that goes around the index prism pivot to apply a constant
    pressure on the gear teeth against the worm to minimize backlash. You
    need a small forceps that lock to grasp the end of the spring and
    manoeuvre the end of the spring into the underside of the index prism,
    this is a frustrating exercise due to the very limited room for
    but necessary. You might be a blt to use a piece of fishing line for
    this but I haven't tried it.
    On Nov 27, 7:08�pm, bruce hamilton  wrote:
    > All times GMT 27 Nov 2008
    > A-10 Sextant with 31.5' index error off the arc (horizon reading is lees
    > than zero in case if am mixed up)
    > Sextant has no other calibration. I frequently get LOP's within 2 miles
    > of my AP so I am happy. It has backlash so I try not to change
    > directions. �I suspect some other error as stars with higher altitudes
    > tend to give me bigger errors.
    > I am actually quite surprised that I am getting a fix that is close
    > enough to find the airport (or Bermuda) if I had do. I have an A-12 and
    > Mark IX, but I only drag out one an evening.
    > Thanks
    > I am presently using CelestNav 3.0 for the palm pilot to work out the
    > sites. I would appreciate any comments on the program. I like it for
    > everything but the fix calculation, but I think 3.0 is only a Beta.
    > AP 49d �16.1 N �123d 7.1 W
    > Pollux � 06:19:33 � 27d �59.3'
    > Vega � �06:16:31 � 13d � �0.3'
    > Betelg � 06:10:53 � 28d �44.3'
    > Altair � �03:56:11 � 22d �37.0'
    > Vega � �03:54:45 � 32d �06.9
    > Capella 03:52:46 � 39d �35.7'
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site