This is a fairly easy method for getting to radius fase for boxes & other curved detail in home workshop.
It is a simple compass for the router, which I made with a long thread & piece of plywood.
I take a board of beech & fixed it on table. After that, I doing moves router back and forth, every time lowering the bit on the router, until it gone under down of detail through it. I leave little thickness.
I was cutting detail by fret saw & after – processing by the router, with template bit.
This is a detail after gluing.