Assessing measurement uncertainty in CMM measurements: comparison of different approaches

Manufactured parts are affected by size and form errors, which need to be assessed against geometrical and dimensional tolerances in order to meet the functional requirements they have been conceived for. The compliance assessment of workpieces with specifications depends on measurements and is unavoidably affected by several uncertainty contributions. According to the geometrical product specifications and verification (GPS), measurement uncertainty consists of method and implementation uncertainty. Literature proposes different approaches for the evaluation of implementation uncertainty, however a standardized method has not been yet achieved. This paper makes an analysis of the various elements to be considered when choosing a specific approach: in the implementation uncertainty of circular features. The most common manufacturing signatures affecting circular profiles were considered, together with the number of points necessary for a reliable estimation of implementation uncertainty.