paul womack
>if the spot and scrape method is accurate when the starting surface is slightly convex--like in the low thousandths. How does the practitioner place the work on the granite plate (or iron lapping plate) and ink it without rocking it?

Proceeed like a mathematician! Scrape (or file, or whatever) a dent in the convexity, and proceed as for a surface that started concave.

Once a small flat (stable!) surface is created in the middle of the sole, expanding it should proceed quite routinely.

BugBear