A few months ago, I taught the Triangle Calligraphers' Guild how to letter in a circle. It wasn't that easy! First, I needed to do my research. I looked through the 60 calligraphic books I have on my bookshelf. There was next to nothing on how to letter in a circle. I then went online to try to find instructions. Again, not real helpful.
So, it finally came down to putting on my mathematical thinking cap and figuring it out myself, in a way that made sense to me.
Above is the final pencil sketch of my idea. The large "A" is a Roman rendition. I think I might need to move it over just a tad to the left for the final piece. The smaller "a"s are Uncial. Inside the inner circle are round Celtic signs.
Below are some of the steps taken to make this sketch.
Use gridded pad and compass to draw a circle.
Using a protractor, lay out lines equidistant, radiating out from the center. Add other circles delineating x-height, ascender height, descender height, etc.
Lay tracing paper over your template, cross your fingers, and start lettering! It might take a few tries to get the spacing just right.
I hope you found this helpful! Now, go and make your lovely letters in a circle! I want to see them!