Abstract A new concept of a tracing system is introduced in this paper, the system being based on the curvature sensing and curvature catering method [1,2] developed by the authors. It can be utilized both for real-time pure tracing by means of the 5-axis machining method and for digitizing and modelling a 3-D pattern with high efficiency. Coupled with CAD/CAM technology (the latter may provide manufacturers with a much higher degree of flexibility) engineering changes can be executed quickly. The so-called curvature-catering method is a new technology offering the most efficient use of a 5-axis machine tool, and ensuring that the envelope formed in one pass and the surface have the same curvature and curvature derivative in the plane normal to the feeding direction. The key point of this new concept is a surface geometric parameter detecting system, consisting of an intelligent probe, an algorithm for recognizing surface geometry, and a posture-control system for keeping the posture of the probe in line with the curvature-catering method. This system can detect the position vector, curvatures, and curvature derivatives at the same time. For pure tracing, the cutter will follow the probe and the surface may be machined with high efficiency. Further, with all this information, the whole surface can be digitized quickly and transformed into a mathematical model.