A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2017 Jan 15, 18:44 -0500
Rember that the device being made is for navigation, not surveying or astronomy. Navigation requires the least precision of the three. Wooden octants were made and used for a very long time, even after the metal sextant - sometimes at the same time. The extra precision and range of a sextant over the octant was to do lunars. A ship's navigator could do morning time sights and noon latitude just fine with a wooden octant.
A small ball bearing used in an electric fan has tolerance of 1/10,000 inch. Small electric motors spin at 8,000 or 9,000 RPM. Press that bearing into hard wood, then use the bearing as the pivot point to fine tune the outside of the arc. The result should be well within the acuracity of an 1800s octant.