Underextrusion

Underextrusion is a defect in 3D printing where the filament is not deposited in sufficient quantity, resulting in gaps or incomplete areas in layers and a weak overall print. It can affect perimeters, infill, and top layers, leading to rough surfaces and poor layer adhesion. It is commonly discussed alongside overextrusion as a contrast in how material is laid down.

Causes of underextrusion fall into several categories. Mechanical issues such as a partially clogged nozzle, a slipping or weak drive gear, or insufficient motor torque can prevent the extruder from pushing filament consistently. Process settings including low extrusion flow or incorrect filament diameter input to the slicer can cause the printer to under-fill. Temperature problems, such as a nozzle that is too cool or fluctuating hot-end temperature, reduce melt flow. Printing too quickly or with high acceleration can outrun the nozzle’s ability to supply material. Filament moisture, especially in materials like nylon or PETG, can cause steam pockets that interrupt extrusion. Other factors include worn or stretched timing components, excessive retraction, and spool tension that causes binding.

Symptoms include visible gaps in layers, thin or incomplete walls, weak infill, poor layer adhesion, and rough or uneven surface finish. Diagnosis often involves verifying extrusion calibration, examining the hot end for clogs, and checking for consistent nozzle temperature.

Common fixes include calibrating the extruder steps per millimeter, confirming accurate filament diameter in the slicer, cleaning or replacing the nozzle, ensuring stable and appropriate print temperature, reducing print speed or flow if needed, and drying filament to remove moisture. Regular maintenance and small test prints help identify and prevent underextrusion.