A dry grinding test of a nano-polycrystalline diamond (NPD) using a polycrystalline diamond (PCD) disc as a truer was conducted to clarify the mechanism of thermochemical reactions to remove chips from the NPD. The PCD disc, in which the cobalt used as a second phase was replaced with several transition metals by electrochemical machining and radio frequency sputtering, was used as a truer. It was verified through the grinding test that at least two types of thermochemical reactions generated and affected layers on the ground surface of the NPD were abraded by diamond grains on the PCD truer. One is an affected layer, in which the covalent binding of diamond was weakened by loosing electrons engaged in the binding owing to the transition metal attracting electrons towards itself. Machining efficiency increased and ground surface roughness became rough with an increase in the electronegativity of transition metals when this type of affected layer was generated. The other type of affected layer is a heat-damaged layer, which has the same crystal structure as a laser- machined surface, formed by the friction heat between the NPD and the truer. A generation of this type of affected layer increased and surface roughness became fine by increasing the specific heat capacity of transition metals.