The Utah Teapot Paperweight 1991

This teapot was introduced in the paper "NC-Machining with G-buffer Method" at SIGGRAPH 91. During the 1980s, the surface patch data of the Utah teapot was widely used as a 3D shape example, and many

computer-generated teapot images were presented in various conferences and journals.

However, nobody had made the Utah teapot as a real 3D solid. In 1990, we developed a simple framework for NC machining with image-processing techniques called the G-buffer method. In our experiments, we used the teapot data and milled a lot of "hemi-teapots." It worked so nicely that we submitted the paper to SIGGRAPH 91. After the paper was accepted, we made a pair of hemi-teapots by milling modeling wax, and ordered 200 Utah teapots of cast metal. This is one of them. We believe it is the first NC-machined Utah teapot in the world.

Technical Overview
This teapot is made of cast metal. The original solid shapes, a pair of hemi-teapots, were milled with a 3-axis NC machine, and the G-buffer method1 was used to control the NC machine. The G-buffer method was originally developed for non-photorealistic rendering, such as edge-enhanced drawing and cross hatching.2

By preparing the G-buffer (z-buffer) with a parallel projection, the various functions required for an NC system are realized with-image processing operations. The functions include tool-path generation, path verification, and feed-rate control. To generate a tool path, for example, it is necessary to obtain the offset surface, which is not easy to calculate from surface patches. However, it can be easily obtained by the convolution with the G-buffer of the surface and the tool-end shape.

Takafumi Saito
Tokyo University of Agriculture and Technology
txsaito (at)

1. Saito, T. & Takahashi, T. 1991. NC machining with G-buffer method. Computer Graphics, 25(4), (Proc. SIGGRAPH 91), 207-216.
2. Saito, T. & Takahashi, T. 1990. Comprehensible rendering of 3-D shapes. Computer Graphics, 24(4), (Proc. SIGGRAPH 90), 197-206.