All along history, humans have always invented, created to improve their standard of liv-ing. Many machines have been built, sometimes simple and others very complex. In order to achieve the best results for customers, machines, industrial plants and humans are moved, displaced and replaced. It is the global humanity technical knowledge that dis-appears. Indeed, there is a lack in the actually conservation methods: sciences and technologies have to be considered and not only architecture. Our heritage research focuses on the mechanical and technical point of view. For instance, in a factory, there is the building but also actua-tors, motors and machines that produce product: taking into account the technical point of view can reach to a better understanding of the past. That's why preserving the national technical patrimony has now become the priority of governments and world organizations. Our approach proposes a new kind of finality: as saving and maintaining physical object cost a lot for museums, and sometimes dismantling is impossible as the machine falls in ruin, we propose to preserve it as a numerical object. The aim of this research is to define the global process and technologies used for imple-menting a numerical model of old machines. The final aim is to constitute a new reference for museologic actors, using actual techniques and methods for putting old machines and technical means in “virtual use”, taking into account the working situation including human being at work. This process is illustrated by an example we performed: a steam engine.