For the proper characterisation of different physical quantities in machine tools, it is obligatory to report the uncertainties connected to the measurements. The uncertainty evaluation according to international standards expresses information of the quality and the reliability of the measurement result. Applications like calibration and compensation are sensitive for the quality of the input data, thus the reliability of the characterisation results need to be interpreted accurately to avoid significant residual errors. General approaches take several factors into consideration during the estimation of measurement uncertainty such as the environmental variations or the uncertainties of the measurement device or the setup. At the same time various repeatable and non-repeatable sources due to the behaviour of the machine tool during the test execution are ignored. This paper highlights the significance of the uncertainty sources connected to the performance of the machine tool itself under quasi-static and loaded condition. The variation of the static stiffness of machine tools, the hysteresis and the play in the system can be even more significant uncertainty sources than the above mentioned ones. Under the framework of Elastically Linked Systems (ELS), a circular test device the loaded double ball bar (LDBB) is used in a case study to identify this effect. The LDBB can be used as a double ball bar and it also enables the measurement of machine tool deflections under quasi-static load. A measurement methodology is proposed to properly describe and demonstrate the variation of the contributing uncertainties associated with repeatability performance of the machine tool. With this approach important interdependencies can be expressed as uncertainty sources and the reliability of the measurements can be increased.
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