Under extrusion is one of the most common issues that can plague 3D prints, resulting in weak, brittle parts with poor layer adhesion. This post provides a comprehensive guide on identifying, diagnosing and resolving under extrusion to help you achieve smooth, high-quality 3D printed parts.
What is Under Extrusion?
Under extrusion occurs when the 3D printer fails to supply enough molten plastic through the nozzle to complete a print layer. This can stem from either a mechanical issue impeding filament flow, or insufficient hot end temperature preventing plastic from properly melting.
Insufficient extrusion manifests visually as thin layers, gaps in the print between extrusion lines, or a “stringy” surface texture. Parts suffering from under extrusion are weaker structurally and prone to layer separation or cracking under stress.
Causes of Under Extrusion
There are several potential causes of under extrusion:
- Clogged Nozzle – Accumulated charred plastic, oxidized buildup, or foreign particulates in the hot end can partially or fully block the nozzle opening, restricting filament flow.
- Filament Slippage – The extruder gear fails to adequately grip and advance the filament, causing slipping and inconsistent extrusion.
- Tight Filament Path – Obstructions or tight clearances along the filament path can impede flow to the nozzle.
- Low Hot End Temperature – If the hot end temperature is too low, the plastic won’t properly melt and flow through the nozzle.
- Loose Filament Drive Gear – A loose or worn extruder gear doesn’t grip and push the filament reliably.
- Calibration Issues – Improper e-steps calibration results in the printer under extruding plastic.
- Cooling Issues – A cooling fan blowing too strongly onto layers can prematurely cool and solidify molten plastic flow.
- Low Print Speeds – Very slow print speeds don’t create enough friction and pressure to force plastic through the nozzle properly.
Diagnosing Under Extrusion
Identifying the specific cause of under extrusion is crucial for applying the appropriate fix. Here are key techniques for diagnosing potential issues:
- Inspect the Nozzle – Check for a visibly clogged or gunked up nozzle. Remove it when cooled and clean out any debris.
- Check Drive Gear Tension – The extruder drive gear should fit tightly on the motor shaft and grip filament with consistent pressure.
- Check for Filament Obstructions – Ensure the filament spool can unroll freely without snagging and inspect the full filament path for blockages.
- Measure Filament Diameter – Use calipers to check for inconsistent filament diameter. Diameter deviations can impede steady extrusion.
- Monitor Nozzle Temperature – Observe if the nozzle temperature fluctuates beyond +/- 5°C of the target temperature during printing, indicating a heating issue.
- Perform a Cold Pull – Force filament through the hot end then allow it to cool and solidify before yanking it out to remove stuck debris.
- Calculate E-Steps – Mark filament with a permanent marker then extrude 100mm of filament and measure the distance actually extruded to dial in e-steps.
- Examine GCODE File – Check for settings in the file that could under-extrude, like low temperatures or low volumetric flow rates.
Resolving Under Extrusion
Once the specific cause is determined, here are effective fixes to get your 3D printer extruding optimally again:
Unclogging the Nozzle
- Perform a cold pull to physically remove debris from the nozzle. Pull out stuck filament while hot, let it cool, then yank to extract clogs.
- Replace the nozzle completely if it’s too gunked up. Use original manufacturer nozzles for best fit and performance.
- For tough clogs, disassemble the hot end and use a narrow wire brush to clean out the melt zone and throat.
Adjusting Drive Gear Tension
- Tighten the extruder idler bolt to increase tension on filament between drive gear and idler.
- Check the extruder drive gear is tightened properly on motor shaft and not slipping.
- Consider upgrading to a geared extruder for more gripping force and torque on filament.
Fixing Filament Path Issues
- Detangle any filament snags on the spool and check spool holder allows free rotation.
- Disassemble hot end and clear any filament obstructions or tight spots in tubing connections.
Tuning Hot End Temperature
- Increase nozzle temperature in 5-10°C increments until extrusion smooths out.
- Perform PID tuning or auto-PID tuning to stabilize hot end temperature control.
- Check thermocouple wiring is intact and replace thermistor if temperature control falters.
Calibrating E-Steps
- Mark 120mm of filament and extrude 100mm, measuring how much was actually extruded.
- Adjust e-steps in firmware according to ratio of expected vs actual extrusion.
- Fine-tune flow rate multiplier for consistent single wall line widths.
Modifying Print Speeds
- For flexible filaments, increase print speed to create more friction heating and flow pressure.
- Slow down initial layer speed to allow strong bed adhesion before speeding up.
- Accelerate and decelerate more gradually between speed changes to prevent abrupt underextrusion.
Hardware Upgrades
- Upgrade to a geared extruder for more torque and gripping power on filament.
- Install a flexible filament guide tube to reduce friction feeding filament to the hot end.
- Change nozzles to 0.6mm or larger diameter for highly viscous filaments like wood or carbon fiber.
Adjusting Cooling
- Reduce fan speeds when printing overhangs, bridges and small parts prone to under extrusion from excessive cooling.
- Modify firmware temperature settings to shut off fans when below a set threshold temperature.
- Design prints with larger features or modify slicing settings like infill to reduce cooling impacts.
Optimizing Slicer Settings
- Adjust filament diameter, flow rate, and extrusion widths for more consistent extrusion.
- Increase nozzle temperature, reduce print speeds and turn off fans for tricky filaments like flexibles.
- Enable filament retractions and optimize retraction settings to prevent ooze and clogging.
- Toggle on “coasting” in slicers to stop extrusion slightly early and prevent blobbing at the end of moves.
While under extrusion can be incredibly frustrating, methodically diagnosing the specific cause and applying targeted solutions will get your printer flowing freely again. Follow these tips to recognize, resolve and prevent under extrusion issues for smooth, well-formed prints. Carefully tuned extrusion is the key to replicating intricate designs and achieving sturdy, functional 3D printed parts.
