Dynamic characteristics of a water jet cutting machine, to be used in a virtual machine implemented in an analysis tool for engineering design, are derived. Machine users need for more cost effective production put demands on faster cutting. Faster cutting results in higher dynamic loads. As a consequence, problems with unwanted vibrations that decrease cutting precision may occur. Prediction of such potential problems is facilitated by an analysis tool for evaluation of suggested design solutions early in the product development process. The present work contributes to ongoing development of such an analysis tool for design engineers. An iterative approach including both theoretical and experimental analysis is applied in order to derive a structural dynamics model of the studied machine. A complex dynamic behaviour of the machine is found. High correlation between results obtained from theoretical and experimental modal analysis implies that the developed model can be used with confidence in future studies of the machine’s total system behaviour.