Estimation of volumetric errors of a machining centre fabricated with conformance to geometric tolerances of ISO 10791 series

Machine-specific ISO standards are internationally well-accepted documents which are broadly used to clarify technical aspects during the trading of different types of machine tools and often are considered as the technical annex of a contract between two sides, manufacturer (seller) and end-user (purchaser). Therefore, these standards are mainly used for pre-acceptance and final acceptance tests to check the accuracy and performance of the machine tool and whether it complies with the agreed technical specifications. Among them, ISO 10791 series address different aspects of accuracy of machining centres as the most applied machine tools in industries. ISO 10791 series specify the tolerances for “general-purpose normal accuracy” machining centres. Regardless of this emphasis, it is seen that some contracts are signed without attention to the required machine tolerances which might fulfil dimensional and geometrical tolerances of the workpieces intended to be finished with that machining centre. In this study, based on the positioning tolerances specified in ISO 10791-4:1998 and the geometric tolerances indicated in ISO/FDIS 10791-2:2022 for vertical machining centres (VMC), probable volumetric errors of a 3-axis C-frame VMC with cross table are investigated for all linear axes equal to 500 mm. In other words, the paper will show that if a VMC with that specified structural loop is fabricated with full conformance to ISO 10791 series, what volumetric errors and its tool path accuracy are achievable. This is a useful indicator for machine tool purchasers and users and the method is applicable to all machine sizes.