Abstract: A centerless grinder having a rotary grinding wheel and a rotary regulating wheel wherein the regulating wheel is adjustable toward and away from the grinding wheel and has its axis of rotation rockable in a substantially horizontal plane. An infinitely variable speed mechanism is coupled to the regulating wheel in such manner as to enable the drive mechanism and the drive coupling to move conjointly with the regulating wheel. The coupling mechanism resists unwanted changes in the speed of rotation of the regulating wheel and absorbs shocks that result from the replacement of finished workpieces with unfinished workpieces.