An ink jet printer mechanism is disclosed in which a print receiving medium is supported in a clamp (18) in a printing station (16) and a print head (41) is traversed through the printing station. A service station (23) for the print head is provided adjacent the printing station and the print head is traversed to the service station between printing operations. The service station includes a carriage (25) which is movable by a drive motor (28) to bring capping and wiping elements (30, 29) into engagement with the print head. A mechanical linkage (33) from the carriage opens the clamp when the capping element is aligned for engagement with the print head.