Filtering effects on involute gear form measurement


 Traditional gear measurement results are used to classify a gear tolerance grade in accordance with ISO 1328-1:2013 but as more stringent requirements are placed on gear performance it is important to be able to properly characterise measurements within a single tolerance grade. However, the measurement uncertainty of the measurement machines is not improving at the same rate as the tolerance requirements, and it is not uncommon to have a sub 10 micron tolerance to be measured with machine with a 1-3 micron uncertainty capability. This breaks the ‘rule of thumb’ that the uncertainty should be smaller than one tenth of the value you are trying to measure. It is therefore important to review the measurement and evaluation process to discern if there are any areas for improvement within our current methods. Additionally, the measurements are being used to refine gear tooth contact analysis performance models and the development of optical and high speed tactile scanning measurement methods is allowing the 3D gear flank surface measurement a feasible option on the shop floor. A greater understanding of the involute flank beyond the standard evaluation limits is required. These developments have prompted a review of the effect that the gaussian filters specified in ISO 1328-1:2013 can have and that they are fully understood by those who must perform and interpret the measurement results. This paper examines the effect that these filters have on measurements where micro geometry corrections or tooth tip and end face chamfers are present. Methods of minimising these effects are reviewed with specific reference to strategies defined in ISO 16610-28:2016 and recommendations are offered to minimise the effects when evaluating the gear tolerance class and quantifying gear flank micro geometry.