Carving the curved moulding above the arch opening, my little pattern above right
 
Carving the curved moulding above the arch opening, my little pattern above right

First I saw and plane smooth the inside radius. Then I use my drawknife to make an even chamfer, and then carve a cove of even dimension all around the curve. Carving a long straight or radius'ed cove, or any type of moulding on furniture or architecture takes careful, dexterous, skillful, patient work. Try and take stock of this when viewing the plethora (all) of our wonderful pre Industrial Age Material Cultural and Decorative Arts. Minds, bodies and hands !!