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    Re: Bubble sextants on e-bay
    From: Douglas Denny
    Date: 2009 Jun 7, 07:17 -0700

    Herewith a pic of the Fairchild A10, including closup of 'new' bubble.
    
    The 45 degree angled horizon glass had to be replaced in this instument too as 
    it was broken.  A new one was cut out of a microscope slide, which was not 
    easy as it was oval in shape.
    
    I used a method taught to me (verbally) by an optical technician who used to 
    glaze spectacles pre and post-WW2 and was the universal method for cutting 
    lenses to shape at the time, as the modern method of glazing machines using a 
    former and diamond wheel were not invented then.
    
    It is to mark both sides with the shape required using a diamond then crush 
    the glass from the outside inwards to the line marked carefully with 
    'snuffers'  - pliars which could have a sideways movement too thus crushing 
    and 'grinding' away the glass at the same time. The diamond marking stops 
    cracks propagating past into the required area of glasss ...if you are lucky!
    I had to just use pliars as I had no 'snuffers' which is why it took four 
    microscope slides before I had it right. The sideways movement makes a lot of 
    difference to crushing efficiency, I have tried it in the past.
    
    Douglas Denny.
    
    Chichester. England.
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