This paper proposes a method to optimize 3D models with complex shapes based on 3D scan models into data that can be machined by 3-axis digital fabrication equipment by utilizing displacement mapping technique. In contemporary architecture, the collage technique is being increasingly used, with complex digital models including 3D scanned objects being used as collaged elements without simplification. Additive manufacturing and subtractive manufacturing are the major techniques used to create these forms, but they are difficult to fabricate on 3-axis machines. This paper first discusses the technical challenges of fabricating collaged models using a 3-axis machine, then the paper proposes a method to optimize the models into data that can be fabricated by 3-axis machines by utilizing displacement mapping technique. The paper introduces two cases of art installations designed and fabricated using the method proposed in this paper and discusses how the method is applied to them. Finally, the potential of this method and challenges to be addressed for the future will be discussed.