How can a printer build a solid object one thin layer at a time?

A filament 3D printer builds an object by laying down thin tracks of softened plastic. Each layer rests on earlier material, so a shape grows upward from a flat platform. A small model boat or a replacement knob can begin as a spool of plastic strand rather than a solid block.

The printer feeds the strand into a heated nozzle. The nozzle softens the material and places it along a planned path. A computer first divides the desired shape into many horizontal slices. Each slice becomes instructions for the nozzle's movements and for the amount of material pushed out. The printer therefore needs both a shape and a plan for making that shape.

For each layer, it can draw an outer wall and then a pattern inside. Many objects do not need to be completely solid; an internal pattern can support the walls while using less material. After one layer, the nozzle and platform move slightly apart in height. The next tracks bond to the material below while they are still warm enough.

An overhanging part may need temporary support beneath it. Very thin layers can show curved surfaces more smoothly, but take more passes to build. The small ridges visible on many prints are evidence of the layered process. The joins between layers can also affect strength, so the direction an object is printed matters.

The printer creates a three-dimensional object by repeating a simple action with carefully changing paths. It cannot put plastic just anywhere in empty air. Its remarkable shapes still depend on heat, support and good contact between one layer and the next.