Operational problems often remain undetected until a machine is commissioned and first machining is attempted. Heavy-duty machines are a specific group of machine tools due to the character of their manufacturing process. As they are often manufactured as single units, which involves high production costs, there are no prototype versions built and no tests are performed on them. Therefore, before the machine is complete, computer simulation methods are often the only validation tools of a machine project at the stage of designing. The variety of applications and the individuality of production are the reasons for the lack of standards defining the rigidity and precision of the cutting process performed by heavy machine tools. In this case analysis, the authors are considering a heavy duty rail wheel lathe, in which some issues were found during its exploitation which make it impossible to achieve the required shape, dimensions and surface finish, while working at set parameters. This article presents a comprehensive approach to the identification of the form and frequency of a machine tool supporting structure’s self-vibrations and their potential sources in the case study of a horizontal lathe for railway wheelsets. The authors, drawing on the results of their long-standing research and their experience in the field of heavy machine tool design and testing, indicate self-excited vibrations as a key factor machine’s operational behaviour, which is rarely considered in this type of machines