A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Peter Monta
Date: 2017 Oct 4, 20:55 -0700
Here is the images of all the tools that I have tried to make. None of them is working.
Ah, rats. I guess the screw requires substantial torque to move, if it can be made to move at all.
Getting a tool from Celestaire sounds like a good idea, provided you're sure the size is the same. My Astra IIIB tool has diameter 4.7 mm and the square hole is 2.1 mm on a side. The corresponding adjustment screws on the sextant have a circular shell with inside diameter 5.0 mm, and the square post on the screw itself is 2.0 mm on a side.
It's possible to drill out the screw. This requires a drill press or milling machine, proper workholding with clamps, support blocks, etc., a way to center the spindle exactly over the hole, and a rigid tool like a center-cutting end mill. Afterwards install a bushing or helicoil insert or similar to bring the threaded hole back to its original state.
If all else fails, and you don't mind modifying the sextant slightly, could you add new adjustment screws near the old ones so that the mirrors rest against the new screws?