Dies for injection molded parts require high-quality surface finishes in terms of both appearance and integrity. Manual finishing by skilled workers is required to produce such surfaces, but this takes several days. To minimize the amount of polishing required, a new finishing technique that employs ultrasonically assisted diamond grinding was proposed in a previous report. Cutting edge truncation prior to grinding is required to produce a mirror surface. In this study, the effect of cutting edge truncation was investigated and the relationships between the ground surface roughness and the cutting torque and the thrust force were considered to optimize the grinding conditions for mirror surface finishing.