Development and validation of a new reference cylindrical gear for pitch measurement

Abstract

A new type of master gear, the Gauge Block Gear (GBG), was developed for the performance verification of coordinate measuring machines (CMMs), for the specific task of pitch and chordal tooth thickness measurement. Its main characteristic is the replacement of the teeth with gauge blocks to achieve direct traceability of the chordal tooth thickness. Mathematical models for the geometrical definition of cylindrical gears with involute toothing, data evaluation, and assessment of the task-related uncertainty, were formulated, and measuring strategies for CMMs were designed and implemented. The GBG was calibrated using the swing round method, and measurement uncertainties on chordal tooth thickness and total pitch deviation F p were determined to be 0.9 μm and 1.4 μm, respectively. Assembly stability and flexibility of the artefact were verified with measurements performed on a CMM provided with general purpose software, one with dedicated gear measuring software, a form tester, and a conventional gear measuring center. Results confirm the correctness of the mathematical models developed to analyze CMM results as well as their compatibility with existing approaches. The Gauge Block Gear provides, therefore, for direct traceability of the chordal tooth thickness and allows the definition of the task-specific uncertainty of pitch and tooth thickness measurements of cylindrical gears as basis for the assessment of the metrological capability of measuring machines.