This paper introduces and illustrates the results of a new method for offsetting the triangular mesh generated from multiple surfaces. The meshes generated from each surface are separated each other and normal directions are different. The face normal vectors are flipped to upward and the lower faces covered by upper faces are deleted. The virtual normal vectors are introduced and used to of feet boundary. It was shown that new method is better than previous methods in offsetting the triangular meshes generated from multiple surfaces. The introduced offset method was applied for 3-axis tool path generation system and tested by NC machining.