Under-extrusion is one of the most common issues in 3D printing, affecting both Bowden and direct drive setups. It occurs when the printer fails to push out enough filament during a print, leading to weak layers, gaps, missing sections, and fragile models.
Whether using a Bowden tube system or a direct drive extruder, diagnosing and fixing under-extrusion is critical to achieving strong, reliable prints. This guide explains the causes of under-extrusion for both systems and provides clear troubleshooting steps to solve it fast.
What Is Under-Extrusion?
Under-extrusion happens when the amount of filament extruded by the printer is less than the amount expected by the slicer.
Signs of under-extrusion include:
- Thin, incomplete layers
- Gaps in the walls or top surfaces
- Clicking or grinding sounds from the extruder
- Poor layer bonding and fragile prints
- Blobs, zits, or inconsistent extrusion along walls
Both Bowden and direct drive printers can experience under-extrusion, though the root causes may differ slightly due to mechanical design.
Key Differences Between Bowden and Direct Drive Systems
Understanding how these two systems operate helps in troubleshooting:
- Bowden Setup: The extruder motor is mounted on the printer frame, pushing filament through a long PTFE tube into the hotend. More friction and flexing occur.
- Direct Drive Setup: The extruder motor is mounted directly on the printhead, pulling and pushing filament with minimal distance, resulting in faster retraction and better handling of flexible filaments.
Each system presents unique challenges when diagnosing under-extrusion.
Common Causes of Under-Extrusion (Both Systems)
1. Clogged or Partially Blocked Nozzle
Over time, filament residue can build up, partially blocking the nozzle and restricting flow.
Symptoms:
- Skipped layers
- Inconsistent extrusion
- Clicking extruder motor
Solution:
- Perform a cold pull to remove debris.
- If necessary, replace the nozzle.
- Clean nozzle regularly using fine wire or needle tools.
2. Incorrect Extruder Steps (E-Steps)
The firmware needs to know how many motor steps are required to move a certain amount of filament. Incorrect E-steps lead to inaccurate extrusion.
Symptoms:
- Consistent under-extrusion across different prints
Solution:
- Calibrate E-steps manually:
- Mark 100mm on filament
- Command 100mm extrusion
- Measure remaining distance
- Adjust E-steps accordingly in firmware or EEPROM
3. Improper Printing Temperature
If the filament is not hot enough, it resists flow through the nozzle.
Symptoms:
- Uneven extrusion
- Nozzle clicking
- Rough surfaces
Solution:
- Increase nozzle temperature by 5°C to 10°C
- Verify the correct temperature for the filament type
- Run a temperature tower to find optimal settings
4. Dirty or Worn Drive Gear
The extruder drive gear grips the filament. If it becomes dirty or worn, slippage can occur.
Symptoms:
- Grinding or stripping filament
- Inconsistent flow
Solution:
- Clean drive gears with a brush or compressed air
- Replace worn gears
- Properly tension the filament against the gear
5. Moist Filament
Moisture absorbed by filament causes bubbling, inconsistent melting, and under-extrusion.
Symptoms:
- Popping sounds during printing
- Rough, inconsistent extrusion
Solution:
- Dry filament before use
- Store filament in airtight containers with desiccants
Bowden-Specific Under-Extrusion Causes
1. PTFE Tube Wear or Blockage
The filament path through a Bowden tube must be smooth. Over time, friction increases due to wear or dirt inside the tube.
Symptoms:
- Increased resistance during manual extrusion
- Jerky filament movement
Solution:
- Replace the PTFE tube if worn or dirty
- Use high-quality Capricorn PTFE tubes for smoother feeding
2. Too Much Retraction
Bowden setups typically require higher retraction settings. Over-retracting causes the hotend to pull molten filament too far, leading to jams.
Symptoms:
- Frequent clogging
- Inconsistent extrusion after retractions
Solution:
- Reduce retraction distance slightly (typical Bowden: 4mm to 6mm)
- Lower retraction speed if necessary
3. Loose Bowden Tube Fittings
If the tube is loose inside its fittings, filament can catch or jam.
Symptoms:
- Random under-extrusion mid-print
- Clicking sounds without obvious cause
Solution:
- Use upgraded metal Bowden couplers
- Insert the PTFE tube fully and lock securely with collet clips
Direct Drive-Specific Under-Extrusion Causes
1. Too Fast Retraction Speeds
Because the filament path is shorter, direct drive setups need slower and shorter retractions.
Symptoms:
- Nozzle jams after rapid movements
- Filament grinding during retracts
Solution:
- Reduce retraction distance to 0.5mm to 2mm
- Lower retraction speed to 20mm/s to 35mm/s
2. Insufficient Extruder Tension
Direct drive extruders may have adjustable tension settings. If too loose, filament slips; if too tight, filament deforms.
Symptoms:
- Clicking sounds without obvious clog
- Flat spots on filament
Solution:
- Adjust tension carefully following the manufacturer’s recommendations
- Aim for firm, not crushing, grip on the filament
3. Overheating Stepper Motors
Direct drive extruders place the motor closer to the hotend. Without cooling, stepper motors can overheat and lose torque, causing missed steps.
Symptoms:
- Skipped steps leading to under-extrusion
- Heat radiating from the extruder motor
Solution:
- Improve cooling around the motor
- Lower motor current settings slightly
- Allow rest periods between prints if necessary
Quick Troubleshooting Checklist
| Symptom | Likely Cause | Solution |
|---|---|---|
| Inconsistent extrusion | Dirty nozzle or worn drive gear | Clean or replace components |
| Clicking sounds during print | Nozzle clog, gear slippage | Clean nozzle, check gear tension |
| Thin or missing layers | Incorrect E-steps, low temp | Calibrate E-steps, increase nozzle temp |
| Jerky filament movement (Bowden) | Worn PTFE tube | Replace with a new tube |
| Skipped steps (Direct drive) | Overheating motor | Improve cooling, adjust motor current |
Common FAQs About Under-Extrusion
How can I tell if my nozzle is partially clogged?
Signs include inconsistent extrusion, clicking sounds, and rough surfaces. A filament flow test or cold pull can confirm if debris is causing problems.
Should I increase flow rate to fix under-extrusion?
Increasing flow can temporarily mask symptoms but does not solve the underlying problem. Always find and fix the root cause instead of adjusting flow as a first step.
What is the best first step if I notice under-extrusion?
Start by checking the nozzle for clogs. Then, verify printing temperature, extruder gear condition, and filament dryness. Systematic checking saves time.
Is under-extrusion more common on Bowden or direct drive printers?
Bowden setups are slightly more prone to under-extrusion due to longer filament paths and increased friction, but direct drives can also suffer from extrusion issues if not properly tuned.
Can slicer settings cause under-extrusion?
Yes. Incorrect flow rate, excessive retraction, or inappropriate layer height to nozzle size ratios can contribute to under-extrusion. Always match slicer profiles carefully to printer hardware.
Conclusion
Under-extrusion can be frustrating, but with systematic troubleshooting, it is almost always fixable. Whether working with a Bowden or a direct drive system, the solution often lies in cleaning, calibrating, adjusting retractions, and maintaining consistent filament quality. With patience and careful tuning, prints can regain full strength, beauty, and reliability. Mastering under-extrusion troubleshooting builds the foundation for consistently excellent 3D printing results.