refresher for a situation most of us will/have run up on. We have a project and know how wide the piece is and we know how tall we want the arc to be to finish it off. This is how to find the radius for the arc that you want.
https://www.mathopenref.com/arcradius.htmlThis should help in setting up your trammel or jig to swing the arc. Set it up and swing a test to make sure that you like the visual results
PS there are a bunch of math/geometry/algebra items at the bottom of the page, maybe you might find something handy