Techniques and systems for 3D printing using mirrors that are oriented at about 45 degrees from an X-axis and Y-axis are described. A technique includes receiving an object model; rotating the object model about 45 degrees around the Z-axis; generating cross-sectional images of the rotated object model; mapping pixels of the cross-sectional images to corresponding mirrors of a digital micromirror device of an additive manufacturing apparatus to form additive-manufacturing images, wherein edges of the mirrors are oriented about 45 degrees from the X-axis of the digital micromirror device and about 45 degrees from the Y-axis of the digital micromirror; and providing the additive manufacturing images to generate a build piece corresponding to the object model. Other implementations can include corresponding systems, apparatus, and computer program products.