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    Re: Astro Compass maintenance
    From: Zvi Doron
    Date: 2005 Mar 24, 19:57 -0000

    Two additional points:
    
    1. Utilising a sudden brain wave I have now tested the alignment of the
    latitude scales by placing a long straight edge on the LHA drum, setting the
    Latitude micrometer to 0 and measuring the height of the ends of the
    straight edge abve the dsk surface with the instrument level. It proved that
    the micrometer is accurate - when set to 0 the LHA drum is perfectly level.
    It is just that the circular latitude scale (indicating 0-9 in white and in
    red) is not perfectly aligned with the micrometer but as its only purpose is
    to indicate units of 10 degrees latitude this is not a problem.
    
    2. In a few books I have including Air Ministry Mual of Air Navigation
    AP1234 it is stated that the knob turning the LHA plates above and below the
    LHA drum should be pushed in to operate it and then pulled out to disengage
    it so that LHA is not changed accidentaly. This is a March 1944 model and it
    seems that it does not have this feature - the knob turns the drum, allbeit
    with a bit of effort required, but it has no push / pull movement as
    described in the books. Is that because it is a later model and the feature
    was not implemented, or is it again a result of hardened grease?
    
    Thanks again for any ideas regarding both my messages.
    
    
    ----- Original Message -----
    From: Zvi Doron 
    To: 
    Sent: 24 March 2005 18:22
    Subject: Astro Compass maintenance
    
    
    > I have just obtained an A.M. (Air Ministry?) Astro Compass  Mk II Ref
    > 6A/1174   4.C.
    >
    > It is in great condition but had been stored for many years and the grease
    > had hardened inside the mecanisms. The bearing plate and the LHA knob are
    a
    > bit hard to turn although functional. The Latitude and declination
    > adjustments are fine, although there is a slight mismatch (about 0.7
    degree)
    > between the main latitue scale and the micrometer drum. The difficulty in
    > turning resembles what happens to Aluminium sextants leke the Freiberger
    > sometimes.
    >
    > My questions -
    > Can the LHA drum be stripped, lubricated and re-assembled easily? It has
    > three screws on each face.
    > Can the bearing plate be dis-assembled and lubricated?
    > What lubricant should I use?
    > Is there a way, using the little screw on the latitude micrmeter drum, to
    > align it perfectly with the main scale?
    >
    > Thanks for any information and happy Easter.
    
    
    

       
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