A cap 13, 15, for the print face 9 of a drop-on-demand ink jet printer moves between a closed position, in which it covers the print nozzles on the print face 9, and an open position in which the print nozzles are uncovered, without requiring movement of the print face 9. In the open position, the cap is recessed relative to the front surface 21 of the printhead. For at least part of the movement of the cap, it is further forward than the print face 9, so that it does not slide across and damage the print nozzles. The drop-on-demand ink jet printer may be used to print onto objects 3 conveyed past it, for example on a packing line. The cap 13, 15, does not obstruct the path of the objects 3 even if they pass very close (e.g. 0.5 mm) to the print face 9 because its uncapped position is further back than the front surface 21 of the printhead.