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Frank,

You questioned making a home shop sextant.  I did just that years ago, before buying my first ( a Davis Mk 3 ).

Make one out of hard wood, maple or oak.  For the pivot use a small ball bearing pressed into a hole near the top of the triangle of wood.  Small, high speed ball bearings are very exact ( like out of a electric fan or hand drill )

Pivot arm from any light, ridiged material, alumumn is what I used.

The scale need not be radial marks on the bottom face like a normal sextant but linear marks on the outer diameter.  Accurate linear scales are easy to find ( think measuring tape - metal or fiberglass ) and a linear vernier is easy to make.

You would not be making a sextant ( no lunars ) but an octant of large radius, maby 20 inch.  A linear scale of centermeters - millameters glued to the wood would work.   Hold the wood triangle by the ball bearing and use a Dremeal tool to sand the correct radius to match the scale.  Put the vernier on the arm using a L shape.

My first try, years ago, was good to 1/10 degree without a vernier.  I just wanted a hands-on model to hold what I was reading about.  With a little skill and time I am sure a handy person could build a sextant to one minute arc.

John H.