The range of and particularly the minimumsurface roughnesses achievable mainly with cemented carbide but also with single crystal diamond round nosed turning and facing inserts has been experimentally studied, machining aluminium and steel on engineering and precision lathes. Characteristic variations of machined surface profile with feed rate as well as insert edge sharpness and roughness measurements are reported. For aluminium faced by carbide inserts on precision lathes, insert edge radius (re) rather than feed marks determined Rz at low feeds, with Rz 0.02re. For steel work material, its properties rather than the insert edge radius became the Rz determining factor.

The range of surface roughnesses, and particularly the minimum roughnesses, achievable mainly with cemented carbide but also with single crystal diamond round nosed turning and facing inserts, has been experimentally studied, machining aluminium on engineering and precision lathes. Insert edge sharpness and roughness measurements and characteristic variations with feed rate of machined surface profile are presented. When machine tool limits are avoided, Rz values down to 0.02 times the insert edge radii have been obtained.