Cutting experiments were conducted on an NC precision cutting apparatus to determine relationship between amount of oil particle on the precut surface and lubricant applying effect. Minute diameter-oil particles could be obtained by accumulation of oil mist which was generated by a spray gun. The amount of the oil particle could be controlled by the accumulation time. Reduction percentage in the cutting forces surely increased with increase of the accumulation time. AFM and ellipsometer analyses indicated that the minimum thickness of the oil film on the precut surfaces which could produce the maximum reduction percentage was approximately 2nm.