Under-extrusion: when a printer lays down less plastic than needed

How to recognise it

You can see it on a first layer that is sparse with gaps between lines, on walls that are full of holes, or on top surfaces where the infill shows through. In FDM printing, plastic is laid down from the nozzle and each line should have an exact width. If it is thinner, the bonds between lines do not form.

Weak bonds mean lower strength. On a functional part, under-extrusion is one of the first things to look for.

Common causes

• A partly clogged nozzle, see clogged nozzle.
• A nozzle temperature that is too low or a speed that is too high, so the plastic does not have time to melt, see nozzle temperature.
• Damp filament that bubbles in the nozzle.
• A badly set flow rate or a worn extruder.
• A tangled or jammed spool.

How to tell it from other flaws

Regularly alternating thinner and thicker layers are usually something else, especially Z-banding. The opposite of under-extrusion is over-extrusion, where there is too much plastic. Moisture and its effect is covered under filament moisture.

It helps to tell the cause by where it appears. If the flaw is there from the very start of the print, it is a setting or a clog. If it appears only later, the cause is often moisture, a tangled spool or overheating in the upper part of the hotend.

For your order

You choose the strength of a part when uploading, from 10 % to 40 % infill. If the model has walls thinner than 1 mm, under-extrusion shows sooner, so give functional parts a thickness of at least several lines, see wall thickness. We photograph every batch before dispatch, but we do not promise in advance that nothing will go wrong.