Abstract: An apparatus for in-situ dressing of threaded type grinding wheels that is more versatile in operation than conventional operator-controlled equipment. The grinding wheel and dressing tool posts are driven by respective motors controlled and synchronized exactly via a fully electronic control circuit, and the grinding wheel motor associates directly with the axis of the grinding wheel in conjunction with two separate encoders, designed to generate dissimilar pulse frequencies; the two encoders can be switched in and out to suit the respective requirements of grinding and dressing operations, so that the output pulse frequency does not rise beyond a level which can effectively be monitored by the control circuit.