The geometry of a product is one of the important factors for manufacturing design such as the design of rigging systems for castings. In this study, several geometry extracting methods were summarized and investigated for general purposes. A fundamental technique to obtain useful information for design of rigging systems was then investigated based on the distance from the surface easily and quickly by using three dimensional CAD data. The algorithm proved very helpful to predict hot spots only from a geometric model, and at least more convenient than the conventional inscribed circle method. An algorithm for the automatic design of risers was also proposed considering the distribution of the distance from the surface. Some examples are indicated to demonstrate that the method is practically useful.