This paper presents a Rapid Pattern Manufacturing system developed for the sand casting process. It involves both additive and subtractive techniques whereby slabs are sequentially bonded and milled using layered toolpaths. As such, patterns are grown in a bottom-up fashion, both eliminating the need for multi-axis operations and allowing small features in deep cavities. Similar approaches exist in the literature; however, this system is specifically targeted at large wood and urethane sand casting patterns. This method introduces a novel support structure approach by integrating a flask into the pattern build process. We also present adaptive slicing algorithms that optimally place layer transitions to avoid thin sections near flats, peaks, and valleys or where interaction with chemically bonded sand could be problematic. The system has been implemented in an automated machine capable of producing patterns in excess of several thousand pounds. Preliminary testing of the system in the development of next generation military equipment is presented in a case study.