An adjustment mechanism (100, 200, 300) comprising: a differential screw that includes a first threaded segment that is connected to a threaded feature of a rigid body (108, 208, 308) of a printer assembly, the first threaded segment having a first pitch, a flexible body, and a second threaded segment that is connected to a threaded feature of the flexible body physically coupled to a print head, the second threaded segment having a different second pitch, wherein the threaded feature of the flexible body is placed in a specific position to optimize at least one region of low stiffness of the flexible body to ensure efficient and accurate rectilinear motion along a single degree of freedom, while limiting undesired motion along the other degrees of freedom, wherein the differential screw connects the rigid body to the flexible body; and an indexing wheel (104, 204, 312) through which the differential screw extends that enables bi-directional adjustment of the print head, wherein said indexing wheel comprises tactile detents to prevent inadvertent adjustments and to enable discrete adjustment increments to reduce total error and a number of steps during print head adjustment, wherein rotating the indexing wheel causes pressure to be applied to or relieved from the flexible body, thereby displacing the print head. a differential screw that includes a first threaded segment that is connected to a threaded feature of a rigid body (108, 208, 308) of a printer assembly, the first threaded segment having a first pitch, a flexible body, and a second threaded segment that is connected to a threaded feature of the flexible body physically coupled to a print head, the second threaded segment having a different second pitch, wherein the threaded feature of the flexible body is placed in a specific position to optimize at least one region of low stiffness of the flexible body to ensure efficient and accurate rectilinear motion along a single degree of freedom, while limiting undesired motion along the other degrees of freedom, wherein the differential screw connects the rigid body to the flexible body; and a rigid body (108, 208, 308) of a printer assembly, the first threaded segment having a first pitch, a flexible body, and a second threaded segment that is connected to a threaded feature of the flexible body physically coupled to a print head, the second threaded segment having a different second pitch, wherein the threaded feature of the flexible body is placed in a specific position to optimize at least one region of low stiffness of the flexible body to ensure efficient and accurate rectilinear motion along a single degree of freedom, while limiting undesired motion along the other degrees of freedom, wherein the differential screw connects the rigid body to the flexible body; and an indexing wheel (104, 204, 312) through which the differential screw extends that enables bi-directional adjustment of the print head, wherein said indexing wheel comprises tactile detents to prevent inadvertent adjustments and to enable discrete adjustment increments to reduce total error and a number of steps during print head adjustment, wherein rotating the indexing wheel causes pressure to be applied to or relieved from the flexible body, thereby displacing the print head.