Abstract: In this study, the effect of the cutting edge radius on a machined surface and subsurface in the nanoscale ductile mode cutting of silicon wafer is investigated through cutting tests using tools with edge radii ranging from 23 nm to 807 nm. The machined surface is examined using SEM, AFM, and Formtracer, with an etching technique used for SEM observation. The results show that if the cutting edge radius does not exceed a certain upper bound value, and the undeformed chip thickness is less than the cutting edge radius, it is possible to achieve both a surface and a subsurface free of cracks. Based on the molecular dynamics simulation of the nanoscale ductile mode cutting process of monocrystalline silicon wafer, it is found that the critical upper bound for the cutting edge radius in the ductile mode chip formation relates to the stress condition in the cutting region. The shear stress decreases as the tool edge radius is increased. As the cutting edge radius increases beyond the limit, the insufficient shear stress will cause both surface and subsurface damage on the machined workpiece. For the cutting of silicon under the same conditions, the limit for the cutting edge radius was found to be about 807 nm. © IMechE 2007.