The increasing complexity of cyber-physical systems poses special challenges for users to be able to appropriate and apply such technologies within their practice. Classic tools to support appropriation have usually taken the form of written manuals or video tutorials. However, recent research regarding appropriation infrastructures and sociable technologies has suggested that appropriation support functionality can be integrated directly into software and cyber-physical systems. The problem confronting this kind of support is the adequate visualization of the information and the provision of user interfaces that could offer the necessary basis for appropriation. Based on the example of 3D printing, we examine how projection mapping-as an innovative form of visualization-can be used as a user interface for hardware-related appropriation support. Through reflections upon the design and evaluation of a projection-based 3D-printer system, we provide insights that extend the notion of appropriation support to encompass projection mapping and that can contribute to the future development of projection-based human-machine interfaces.