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    Re: Fluids for Bubble Sextants and Sealing Methods
    From: Paul Dolkas
    Date: 2015 Dec 28, 21:25 -0800

    I got sick and tired of having to chase that small ball bearing around every time I filled up my sainted Link 12 (which is every few days because of a tiny leak in the pre-WW11 bubble chamber), so I replaced it with a pan-head screw with an integral o-ring under the head. (http://www.mcmaster.com/#machine-screws/=10g04m7). You have a choice of o-ring materials: fluoroelastomer is probably the safest bet. I had to trim the length of mine to avoid the threads bottoming out before the o-ring sealed. This is a much more practical solution than the ball bearing design.


    Paul Dolkas


    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Robert Eno
    Sent: Monday, December 28, 2015 6:25 PM
    To: paul{at}dolkas.net
    Subject: [NavList] Re: Fluids for Bubble Sextants and Sealing Methods


    I have re-filled my Mk IX RAE sextant and my C.Plath marine sextant bubble attachment (the pre-Litton Industries model) with hexane and have found it to be an ideal liquid for this purpose. In my case, and due to my location, using a liquid with a very low freezing point is a major consideration.


    I would not recommend anything viscous like kerosene or compass fluid as the bubble in these liquids is relatively sluggish; more so in colder conditions.




    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Robert Swartz
    Sent: December-28-15 4:25 PM
    To: enoid{at}northwestel.net
    Subject: [NavList] Re: Fluids for Bubble Sextants and Sealing Methods



    There is nothing in the Link literature on the mounting order of the sun shades,

    Both bubble chambers should have Bristol set screw filler plugs with either small ball bearings inserted or, in the case of early A-12s, points on the end of the filler plugs.

    Refilling bubble chambers was part of routine maintenance of bubble sextants--The integrity of the filling depends on the seals and the tightness of the filler plugs (which I also seal w/liquid shellac) after filling the chambers w/ xylene.

    Your sextant is severly out of calibration and probably needs an overhaul. I calibrate the sextants I sell to 1-2 minutes of arc using a Link Collimator. You can use the natural horizin at the shore of a large lake or the sea under calm conditions as a zero datum. You can also use Polaris from a known latitude (requires correction tables in the Nautical Almanac).

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