This paper shows the process followed in the assembly of the different elements of a stationary invention by Henry Muncaster, specifically of a two-cylinder entablature steam engine with parallel motion crosshead whose plans were published in the magazine ‘Model Engineer’ in 1957 as a preliminary step in order to explain the operation of the invention. To do this, the Autodesk Inventor Professional 2024 software was used, finally obtaining a coherent and functional 3D CAD model. However, there have been drawbacks derived from the absence of dimensions in the available plans of the invention and certain inconsistencies, which is why a series of hypotheses have had to be established about the geometries of some elements, estimating their dimension and applying a series of dimensional, geometric and movement constraints (degrees of freedom). On the other hand, one of the drawbacks detected with the use of the Autodesk Inventor Professional software arose when assembling the invention, since the software does not take into account the deformation of components manufactured with elastomeric materials such as the drive belt. Finally, graphic documentation consisting of assembly plans and assembly perspectives was obtained.