In the sixteenth century we witness a large circulation of the vernacular translation of Vitruvius’ De architectura and of treatises on Greek mechanics. In this period, the technicians begin to pay attention to the utility of the geometrical principles to design buildings and machines. In this context Guidobaldo del Monte writes the Mechanicorum Liber. In this text, Guidobaldo defends the idea that geometry must be placed at the basis of the practical realisation of simple machines. To better explain his point of view, Guidobaldo combines the geometrical representation, more suitable for the analysis of constraint reactions, with the three-dimensional representation, typical of the visual culture of technicians, to illustrate a same object. By examining the description of the machine Axis in the wheel contained in the Mechanicorum Liber, we argue in favour of the importance of three-dimensional and geometrical representation of the same machine to make the functioning of the mechanical components more understandable to architects, engineers and builders.