Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Backlash
    From: Clive Sutherland
    Date: 2005 Nov 21, 20:42 -0000

    Some years ago when I was servicing a sextant for a friend I noticed an
    excessive and variable (i.e. dependant on the part of the arc being used)
    backlash problem.My surmise was that at sometime during its life the index
    micrometer worm had been clumsily grated across the gear arc, and back lash
    was occurring wherever the worm did not now properly engage. This only
    occurred
    only over certain parts of the arc, mostly near the parking position, as the
    sextant was put away in its box.
    
    This could occur on a sextant if the clamping lever had been insufficiently
    gripped as the index arm was rapidly moved and the teeth on the gear (which
    was made of a hard metal) come into contact with the softer arc and damage
    the tops of some the teeth. If you were to look at the shape of the damaged
    teeth in  profile their normal triangular shape would be turned into that of
    a breaking wave.
    
    My thoughts are that If you find backlash occurring on a old or second hand
    sextant or anytime on
    a plastic one, look carefully at the shape of the gear teeth. If any damage
    is not very bad It may be carefully repaired. But!  Beware, always look very
    carefully if you are buying second hand. Even a new plastic sextant is not
    immune, especially if "shop soiled!"  This, in my opinion, is the greatest
    risk with plastic sextants. They do need Extra Tender Loving Care!
    
    CLIVE
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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