These methods require two simple tools; one you already have and another that can be made in less than five minutes.
This story is less about tools than it is about know-how. With these two methods there is almost nothing that can’t be scribed to a perfect fit. One is a boat-building technique called spiling; the other doesn’t have a name, but makes use of something called a joggle stick.
You can see the story on the JLC website by clicking here. I wrote it when I was a finish carpenter. I can’t take credit for either technique; they were taught to me in boat-building school in the 80s. It has been years since I built a boat and yet I use these methods to this day, most recently to scribe new treads into an existing closed-stringer stair.