Flow in 3D printing: how much plastic is extruded

What flow sets

The slicer works out how much plastic each line needs, and the extruder feeds it. Real filament is not perfectly round, though, and each material behaves a little differently when melted, so a flow ratio is added. Its tuning and its relation to pressure advance are described in the OrcaSlicer wiki. The filament diameter is related to it as well.

Signs of wrong flow

• Too little. Under-extrusion: gaps between lines, thin walls, and a weaker and smaller part.
• Too much. Over-extrusion: blobs, bulging walls, elephant foot and dimensions larger than in the model.
• Uneven. Poor filament, moisture, a worn nozzle or a partial clog give alternately thick and thin spots.

Flow and dimensions

With precise parts, correct flow shows up in the tolerances. A wrong setting, even by a few percent, changes the wall thickness and how components fit. That is why flow is calibrated for each material, and with tolerance-sensitive parts a margin is allowed for. See also wall thickness.

Flow and strength. Correct flow is also a condition of strength. With a shortage of plastic the lines stand apart, and the part is brittle and porous. With an excess the surface is lumpy and accuracy drops. Infill and walls are affected equally, see infill.

Flow in your order

We have calibrated the flow for PLA and PETG ourselves, and you do not set it in the calculator. If you need two parts to fit together precisely, design a gap of at least 0.2 mm and see tolerances. We do not promise very precise dimensions, as FDM printing is naturally tolerant to fractions of a millimetre.