A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Geoffrey Kolbe
Date: 2016 Mar 27, 07:37 +0100
For a start, Geoffrey, the frames of sextants were not brass, a copper-zinc alloy of dubious corrosion resistance, but bronze, whose main constituents were copper and tin.
This is a tough and tenacious metal and one has to remember that the instrument maker in the late eighteenth and early nineteenth centuries used man-powered lathes, so turning a large radius was difficult. The metal had hard spots that could deviate the stylus of the dividing engine, so a dovetail was cut into the limb and a sliver of silver whose section was a segment of a circle was hammered into the dovetail and filed or turned flush.