Contact accuracy and orientations affecting the lapped tool sharpness of diamond cutting tools by mechanical lapping

In this paper, a brittle–ductile transition lapping mechanism is proposed for the mechanical lapping of single crystal diamond cutting tools. The critical depths of cut for brittle–ductile transition and the dynamic critical tensile stress are regarded as the references to analyze the influence of contact accuracy between the rapid rotating scaife and lapped tool surface and the effects of tool face orientation on the sharpened cutting edge radius, respectively. The experimental results indicate that the vibrations of lapping setup, surface quality of scaife, dynamic balance and motion accuracy of the spindle, lapping compression force and lapping velocity all have enormous influences on the contact accuracy so as to affect the lapped cutting edge radius of diamond cutting tools. Under the optimal settings of each influencing factor for a robust contact accuracy, a perfect diamond cutting tool is sharpened in ductile lapping mode with a cutting edge radius of 30–40 nm and a surface roughness Ra of 0.7 nm on the tool rake face. On the other side, different orientation settings of tool faces enable diamond cutting tools edge to have different micro mechanical strength. Under the same configurations of the lapping parameters, the higher the micro mechanical strength of tool cutting edge is, the smaller the sharpened cutting edge radius would be.