Some of the items
I have made up for use with the Mk IX bubble Sextant.
You can replace
a filament "Bulb" with an LED, or, as I do, make up
the brass parts as well.
Eye Guard, Original
and some early attempts!
An original (left) with a typical production version for comparison
Home brew eye
guard mounted on one of my Mk IXs
I use a penny for the contacts, not sure about the legalities
but it works well.
How to check lamp socket polarity
A few of my sextants had scruffy mirrors
and the thoughts were to re silver them or try replacing them
with modern glass mirror. I located some mirror made of float
glass, I could not get the same thickness so decided to go for
thinner material. I cut the glass to size, ground the edges and
because I noticed that the screws for the adjusters were removing
the silver on the originals I coated the mirror backs with epoxy
and placed some pads of stainless steel where the screws would
make contact. The end result you see below.
I later realised that I could use as
a hard backing, microscope slides. These I cut to size and glue
onto the back of the mirror instead of the steel pads. These work
well. Overall thickness is the same as the originals so fitting
is not a problem. The same warning of course about the slight
difference in thickness applies.
The center mirror is viewed from the
front, it is flanked by two back views showing the epoxy and steel
pads. The outer pair are the backs after a couple of coats of
gold paint. Optically the mirrors seem no different to the originals,
though theoretically, because of the different thickness of the
glass, there will be a increasing error as one gets away from
0°. Once I adjusted the sextant I have done trials that seem,
to all intents and purposes, to show the sextant works as well
as when it had its original mirrors.
Above are shown a new Mk IX Prism cover.
All the original ones I have seen are either a light orange or
a deep red. This is an effect caused by age and they should be
clear. I thought. WRONG! They should be a light orange colour.
The clear ones I make I have found allow too much light in when
pointing at the sun. I have had to add an extra light orange filter
on top of the existing internal filter above the bubble chamber.
If your bubble is difficult to see in daylight, but seems OK with
the internal lamp at night,try removing the cover as a test. It
may well have become too dark.
Most of my sextants have either lost
some or all of their bubble chamber lamp filters. These are the
small circular pieces to the right of the prism cover. I made
mine out of modern plastic stage lighting filters. The originals
are made of gelatine and will dissolve in water.
The bottom shot is of a replacement
logging tablet I made. It is printed, not engraved and is more
for appearance than utility.
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