Alongside the macro test parameters on tooth flanks for profile and tooth traces, surface
properties (roughness) play a decisive role in ensuring proper toothed gear function. This
article addresses roughness measurement systems on tooth flanks. In addition to universal
test equipment, modified test equipment based on the profile method for use on gears is
addressed in particular. The equipment application here refers to cylindrical gear flanks and
bevel gear flanks. The most important roughness parameters, as well as the implementation
of the precise measurement procedure will also be described under consideration of the
applicable DIN EN ISO standards as well as the current VDI/VDE Directive 2612 Sheet 5.
Surface roughness measuring of gear teeth can be a very frustrating experience. Measuring results often do not correlate with any functional characteristic, and many users think that they need not bother measuring surface roughness, since the teeth are burnished in operation. They mistakenly believe that the roughness disappears in a short amount of time. This is a myth! The surface indeed is shiny, but it still has considerable roughness. In fact, tests indicate that burnishing only reduces the initial roughness by approximately 25%.
The working surfaces of gear teeth are often the result of several machining operations. The surface texture imparted by the manufacturing process affects many of the gear's functional characteristics. To ensure proper operation of the final assembly, a gear's surface texture characteristics, such as waviness and roughness, can be evaluated with modern metrology instruments.
