Celestaire Bubble Horizon Adapter for Davis Sextants
by biketool, published
Press fit adapter for Celestaire Practice Bubble Horizon AKA artificial horizon to fit Davis Mk12, Mk15, and Mk25 plastic sextants. The alternative is to purchase a very expensive commercial navigators sextant, using a bowl of water or puddle sun reflection, or buying folding water box for reflecting the sun which Davis actually sells for inland practice. Cost is an important consideration now that a sextant is mostly a backup and hobby tool replaced in frontline navigation by GPS. Requires no boresighting or adjustment of either the sight, tube, or sextant as the bubble will always gravity align itself with the horizon line in the artificial horizon. Get the bubble horizon here https://www.celestaire.com/sextant-accessories/practice-bubble-horizon-detail.html
An artificial horizon sight is required for celestial navigation any time a good sea horizon is not viewable due to weather, terrain, or an inland location; you do need to know your altitude above sea level though by either a map, survey mark, or properly adjusted altimeter; use air sextant altitude correction tables when above mean sea level. This initially incompatible sextant and artificial horizon combination when joined together with this adapter forms the most affordable off-the-shelf inland, airborne, and bad weather celestial navigation tool currently available.
The Celestaire sight uses a horizontal slit to force proper eye alignment, this makes it less useful than a two axis bubble sight for shooting smaller stars after dark. Don't be concerned that the horizon side of the mirror is blocked by the bubble, you now align the the center of the bubble with the horizon line then adjust the sextant to allign a celestial object to the black line as you would with the sea horizon, it is a bit more work to allign three objects than the regular sun and horizon. Continue to use sun filters for both mirrors as required.
The Celestaire bubble horizon should still work on full size sextants with fork mount sights it was designed for while this adapter is installed.
This adapter printed in ABS has been in use for several years without any problems.
Print at 10% size be sure to use a slic3r ratio of 1.0 for infill and adjust your filament ratio so your walls will be fused properly.
Press fit the more narrow end(22mm) into artificial horizon, you need not cut off the Plath/Tamiya fork mounts for standard sextants unless you want, larger(23mm) tube end fits into the friction fit telescope mount on Davis plastic sextants. This may appear wrong size but the inside of the Celestaire sight sun shade tapers inward to a cylindrical area, tests show a perfect hand tight fit in the sight and proper removable friction fit in the sextant.