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    Re: A-10 Sextant Manual
    From: Douglas Denny
    Date: 2009 Jun 11, 04:56 -0700

    Hello Bill,
    
    The worm assembly came apart very easily. I made a simple crude anvil to 
    back-up the shaft to remove the pins (picture) it being essential to prevent 
    any distortion of the shaft whilst driving the pins out.  They came out quite 
    easily.
    It is also essential to be very careful indeed to remove the shaft without 
    touching the threads as the clearence through the upper bearing is not much.
    ------------
    
    I am not impressed by the use of this method of position fixing for the shaft 
    axially, even if used elsewhere in engineering. In this instance 
    particularly, the bearing surface of the shaft diameter on the washer must 
    only be a fraction of a mm creating a very small annulus of bearing on the 
    washer, and any piece of dust/grit or other detritus getting between will 
    cause trouble. It also has friction that should be avoided at this point 
    which would be eliminated with a proper bearing. Also, if the washer is 
    slightly bent or out of true and/or the shaft bearing edge not true then 
    there will be an up and down movement on 360 degree rotation of the 
    shaft(unless the washer travels with the shaft rotation which is unlikely 
    with the greater friction of the washer on the bearing boss).  The best 
    practice method here should have been a small taper-roller bearing.  As there 
    is room between the helical gear onthe shaft, and the bearing boss I shall 
    investigate the possibility of replacing the crude shaft/washer end-thrust 
    bearing with a taper-roller beraing. It should not be too difficult to do and 
    if I can get a bearing with internal diam the same as the shaft diam then I 
    am home and dry - otherwise a bit of lathe work on the worm shaft is 
    necessary.  Can be done without too much trouble I reckon.
    --------
    
    I have not modified the sextant in any way (yet) the ball-race bearing you see is as seen when opened.
    
    Regards,
    
    Douglas Denny.
    
    Chcihester. England.
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