Step 1 of the physical globe construction involves shaping the perfect sphere. How to do this? The globe must be perfect, down to the millimeter, since all the gores must fit together perfectly upon the surface of the globe. I thought about tracing a circle myself as a template, so as to produce a template in which I could apply plaster to a lightweight core. Honestly, though, there is no way I can get the precision in a template through any manual cutting method that I can imagine.
So, off to the local machine shop. They have a huge flatbed laser-cutting machine that can cut to a precision of +-0.003. Works for me. The result, as shown below, is a 30″ 10-gauge galvanized steel template, with guides spaced every 10 degrees.
It worked out pretty well, I think. Now to frame it up and devise a retractable axis to serve as the central rotation point.