CNC Turning is an intricate and detailed method of creating custom parts and components using a lathe or turning center. Turning is a machining process that uses stationary tools with your material rotating. Typically parts that need this process have mostly circular/round features. Turning provides a superior concentricity than milling and also proves to hold tighter tolerances in round features.
CNC Milling is a machining process with rotating cutting tools while the material is held stationary. This process is typically used in parts that have a box like appearance. Other attributes that may make milling a better options over turning are larger pieces, features that are not on centerline, and prototype parts.