The dynamics of grinding is less well investigated than other machining processes. In particular, the cylindrical cup grinding process used in optical manufacturing has received little attention. Our interest in this arises from the observation of rose-petal shaped marks called cutter marks during microgrinding glass lenses. Since microgrinding is a finish grinding process supposed to reduce greatly the amount of material to be removed in the polishing stage, it is important to find the cause of, and to eliminate, these cutter marks.