A rotary controller selectively-disengageable locking knob assembly, including a hub having a longitudinal axis and an axial bore extending at least partially through the inner hub along the longitudinal axis, wherein the axial bore is configured to receive a shaft of a rotary controller arranged in or on a device surface. The hub includes a radial bore extending from an outer surface of the hub to the axial bore, wherein the radial bore is perpendicular to the axial bore. A knob is concentrically disposed about at least a portion of the hub, wherein the knob includes at least one central bore structured to receive at least a portion of the hub, a radial slot alignable with the radial bore, and a circumferential bottom surface having a first engagement arrangement. The knob is axially moveable on the hub to selectively disengage the first engagement arrangement from contact with the second engagement arrangement.