This work presents halftoning techniques to manufacture 3D objects with the appearance of full grayscale imagery for Fused Deposition Modeling (FDM) printers. While droplet-based dithering is a common halftoning technique, this is not applicable to FDM printing, since FDM builds up objects by extruding material in semi-continuous paths. A set of three methods is presented which apply a linear halftoning principle called 'hatching' to horizontal, vertical and diagonal surfaces. These methods are better suited to FDM compared to other halftoning methods: their applicability stands irrespective of the geometry and surface slope and the perceived tone is less sensitive to the viewing angle. Furthermore, the methods have little effect on printing time. Experiments on a dual-nozzle FDM printer show promising results. Future work is required to optimize the interaction between the presented methods.