Circular cylindrical tracks do not fill space. To solve this problem, they can be printed with some overlap (smaller spacing than their diameter) or with a flat-tipped nozzle at a layer height smaller than the extrudate (nozzle) diameter, both of which cause lateral spreading of the resin into the void space between tracks before solidification. Consider tracks of diameter D printed at a spacing (center-to-center) of D, but with a flat-tipped nozzle. If the neighboring track is solid and all the spreading of the resin is lateral (i.e., sideways in the cross-section view), show that a flat track (layer) height reduced to about 0.78D would just completely fill space. The drawing shows the shape of the track cross-sections (black) just filling the void space between tracks. This assumes the curvature of the liquid surface of the track being printed (right) stays constant at D and all the lateral spreading is into porosity between the neighboring track (left). Note that the equivalent rectangular track cross- section (red) has width D and the same area as the undeformed circular tracks (blue).