Some problems in gear metrology

Abstract

The inspection of each individual tooth element of a spur gear wheel can be a tedious and expensive process. Two methods of composite gear testing are available, namely, the single flank rolling gear test and the dual flank rolling gear test. The first method is well documented, but the dual flank system tends to have been neglected, few papers being available on the subject. As a preliminary stage to the investigation into the dual flank testing technique two methods of pitch error measurement using ball ended contact probes are examined. These are :(i) the direct measurement of cumulative pitch measurement using a single contact probe and dividing arrangement and(ii) the span gauging of adjacent teeth, commercial measuring equipment being used in both cases. The two methods are compared theoretically in terms of the maximum cumulative pitch error of a gear, and their probable accuracy of measurement compared with the allowable pitch tolerances quoted in the relevant British Standard. Specifications, a theory for the dual flank test is developed relating the variation in centre distance of a pair of gears in close mesh to the errors in tooth pitch and involute profile. The validity of the theory- is tested by experimental measurements, on actual gears, and- a means of determining the permissible variation in the dual flank test error trace from the allowable tolerances on tooth pitch error and tooth profile error suggested. The identification of the type of elemental error from the pattern of the dual flank trace is also examined together with the limitations of the test.