Abstract: A computer-controlled apparatus and method for fabricating three-dimensional articles in layerwise fashion is disclosed. Upon dispensing a layer of a fusible powder, a laser irradiates selected locations of that layer to fuse the powder into a cross-section of the article to be formed in that layer, such that the fused cross-sections fuse together into the article. The laser is controlled in a raster scan fashion across the selected locations of the powder layer. The parallel raster scan lines are separated from one another, centerline-to-centerline, according to a selected pitch, or fill scan spacing value. The positions of the parallel scan lines are determined with respect to a coordinate system at the powder layer, rather than with respect to boundaries of the cross-section being formed; in alternating layers, the parallel scan lines are offset from one another by one-half the pitch.