100 printhead 105 and lift mechanism and a maintenance system 504 comprising the maintenance sled 200 transport mechanism and maintenance modules the ink delivery system 502 may be of the type described in u s pat no 8 485 619 the contents of which are incorporated herein by reference for example the ink delivery system 502 may be a circulatory system having an ink container which delivers ink to inlet ports 105 of the printhead cartridge 102 and receives ink from outlet ports 107 of the printhead cartridge various printing purging pressure priming and depriming operations may be coordinated via a pump and valve arrangement of the ink delivery system as described in u s pat no 8 485 619 however it will of course be appreciated that other ink delivery systems may be used as known in the art the controller 500 coordinates all maintenance and printing operations via suitable signal communication with the ink delivery system 502 and maintenance system 504 as well as the print bar system 503 and media feed mechanism 501 the print bar carriage 100 is slidably liftable relative to the housing 10 along a nominal z axis using a rack and pinion lift mechanism referring initially to fig7 the rack and pinion lift mechanism comprises first and second toothed racks 110 and 112 fixedly mounted to respective first and.