In this paper, a new approach is presented to construct the G-buffer models by finding 3D shape-generating profiles of milling cutters. The G-buffer method is commonly used in 3-axis machining verification. In this paper, the analytic 3D shape-generating profiles are formulated to construct the swept envelope in 5-axis tool motion. The 5-axis machining G-buffer model is updated by the constructed swept envelope. The techniques presented in this paper can be used for 5-axis tool path generation and the machined surface error analysis.