SEXTANT PROJECT - Part Two

In his excellent book, The Nautical Sextant, W.J. Morris describes in intricate detail how to refurbish an old sextant, such as my Simex. I’ve been following his procedure as closely as I’m able. The first phase is disassembly, which after a little more than a month I’ve gotten to the end of it. Morris describes altering and using thin blade screw drivers to take apart the various components while not buggering up the screw heads.

I (mostly) got everything disassembled. One trick he revealed is to be patient with penetrating oil to get into seized threads to loosen stuck screws. I had to let a couple of them sit for a week or so; but now everything is free that needs to come off.

I proceeded with corrosion and tarnish removal. So far I’ve gotten the big pieces fairly cleaned, more detailed work will have to happen on some specific areas: the track in the scale arc, the battery connections for the lamp, and some of the more fragile of the sunscreens.

The best overall method I’ve used so far was vinegar baths, a surprisingly good way to get years of corrosion off the brass and aluminum. Some places will need metal polish, which is where I am at the moment. My intention is not to bring the sextant back to some new-looking, flawless finish, but to get it instead into “working” order and corrosion free. It’ll still look like an old sextant with paint missing, etc. I don’t want a museum piece, just a useful instrument that looks like it belongs on a boat.

Since I’ve had long experience with telescopes I wasn’t hesitant to take apart the small galilean scope and get it back to working order. The vinegar baths took care of the external and internal brass parts and my secret lens cleaner formula has the lenses spotless and protected. The little scope is back together now (with a trace amount of Liberty clock oil to keep things free and moveable).
 

Galilean scope brass parts de-corroded.

Meanwhile the horizon mirror has been sent off for re-silvering, (I was lucky that the index mirror is still serviceable and nearly flawless.) which takes a while to complete. There’s only a few places in the world now that know how to re-silver sextant mirrors and they do them in batches when they have acquired a certain number of them. The really helpful guys I chose were Island Marine Instruments Co. in Everett, WA.

‘Tween now and Christmas I’m busy doing spot corrosion removal on the frame, adjusting the index arm and micrometer, and hunting down a new bulb for the little arc lamp.

It’s all going well, I think.