Abstract: In the field of Computational Geometry, the design of 3D models using hand drawn strokes has been well-studied in recent years as a way to improve user interfaces. When using hand-drawn strokes to design 3D models, an algorithm for cutting a model by a stroke is required. Previous algorithms have concentrated on precision and are expensive to implement. This paper gives priority to simplicity and robustness rather than precision. Firstly, mesh vertices near to the stroke are moved so that they lie on the stroke, to avoid numerical error. Then the stroke is simplified so that it crosses a triangle at most two times. With this approach, the number of patterns of triangle division that a system has to implement is reduced to only three. This reduces the time a developer must take to implement a cut operation for a sketching interface.