(57) A franking machine contains a printing head which itself includes at least one print face on the underside thereof which, when inked, will form an impression on the surface of an envelope or packet placed on the platen wherein the printing head is pivotally attached to a freely pivoted arm with the axis of pivoting parallel to and closely spaced from the plane containing the print face (or lies in the plane containing the print face) so as to reduce sliding movement of the print face relative to an envelope or packet during downward movement of the printing head, a non-gravitational centering device resiliently holds the printing head in a fixed orientation relative to the freely pivoted arm and a thrust means is provided for exerting a thrust on the arm in a direction and at a position relative to the pivotal attachment of the arm to the remainder of the franking machine, to urge the end of the arm carrying the printing head in a generally downward direction towards the platen during a printing operation.