NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble sextants on e-bay
From: Douglas Denny
Date: 2009 Jun 7, 07:17 -0700
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. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---