A method that pertains to design of the optimal form-cutting-tool for machining of a given sculptured surface on a multi-axis NC machine is discussed in the paper. The results reported in the paper are based in much on the author’s previous work in the field of R -mapping of a sculptured surface onto the machining surface of cutting tools. Mathematical foundations of a novel method of experimental modeling of the interaction of the form-cutting-tool and the work are disclosed. The last method is of critical importance for the experimental determination of the rate of conformity functions, those essential for consequent use of R -mapping of surfaces. The presented geometric criteria is helpful for designers since the maximal rate of conformity of the generating surface of the form-cutting-tool to the sculptured surface is a prerequisite for the development of extremely efficient machining operations, and in solving design problems. The results of the research reported in this paper can be considered as a portion of the DG/K -method of surface generation on a multi-axis NC machine earlier developed 1 The DG/K -method of surface generation is based on fundamental results obtained in differential geometry of surfaces and in kinematics of multi-parametric motion of a rigid body in E 3 space (See: Radzevich, S.P., Sculptured Surface Machining on Multi-Axis NC Machine. Monograph , Kiev, Vishcha Shkola Publishers, 1991, 192p. – Copy of the monograph is available from the library of congress, and Radzevich, S.P., Fundamentals of Surface Generation. Monograph , Kiev, Rastan, 2001, 592p. – Copy of the monograph is available from The Library of Congress). 1 by the author. The method is based on the extensive use of reliable results worked out in classical differential geometry of surfaces. Topics covered in the paper enables one designing the form-cutting-tool for optimal machining of a given sculptured surface on a multi-axis NC machine. The usefulness of the approach is verified from two simple examples that are clear and easy for understanding.