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3D Printing Guide

How To Fix 3D Printer Under Extrusion

Picture of Scott Gabdullin
Scott Gabdullin

Updated on January 31, 2025

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After meticulously calibrating your machine, selecting the ideal filament, and dedicating hours to your design, weak layers, gaps, or uneven surfaces can ruin your print. Under-extrusion is a significant challenge in the workflow of any professional in 3D printing. Fortunately, resolving it doesn’t require a complete overhaul of your setup.

Whether it’s an issue with your filament, hardware, or slicer settings, it’s just a calculated approach to identifying and addressing the root cause. Let’s break down under-extrusion into manageable pieces, offering practical steps to restore your printer’s performance.

What Happens When a 3D Printer Is Under Extrusion?

Under-extrusion occurs when your 3D printer’s extruder assembly fails to deliver enough filament to produce a solid, continuous layer. Instead of smooth, cohesive prints, you are left with gaps, weak layers, or incomplete sections. 

Unlike a total extrusion failure, under-extrusion can be subtle, showing irregularities in the walls, thin layers, or surfaces that seem stingy or brittle. When a 3D printer fails to extrude enough filament, several issues arise that can render prints unusable or aesthetically flawed. It disrupts the printing process, leading to compromised quality and functionality of the final product.

One common indicator is the presence of gaps in the top or side layers, where layers appear incomplete or feature visible holes, disrupting the smoothness and integrity of the print. These incomplete areas occur because the filament flow is insufficient to fill the intended volume. As a result, the print may have weak spots or missing sections that affect its structural integrity.

Another consequence is poor layer adhesion. Without a consistent flow of material, the layers of a print may not bond properly, creating weak points that make the object fragile or prone to breaking under pressure. This lack of strength can be especially problematic for functional parts or prototypes.

Under-extrusion also leads to rough or uneven surfaces. The insufficient extrusion causes inconsistent patterns, resulting in a finish that is far from smooth. These irregularities can be visually unappealing and may require additional post-processing to correct.

Additionally, under-extrusion can waste valuable time and resources. Prints affected by this issue often need to be scrapped, requiring reprints and consuming extra filament. For professionals, this can lead to delays and increased costs, particularly in time-sensitive projects.

Common Causes of Under Extrusion

Under-extrusion can stem from several common causes, each impacting the printer’s ability to maintain a consistent filament flow.

Clogged Nozzle

Residual material, such as hardened filament or debris from previous prints, can obstruct the nozzle opening, preventing proper filament flow. This blockage leads to uneven extrusion or complete failure, often requiring cleaning or nozzle replacement to restore functionality. 

Wrong Filament Diameter

Using filament with an incorrect diameter for your printer can cause uneven extrusion. When the filament is too thick, it can jam the extruder, while filament that is too thin may not provide enough material for proper layer formation. 

Additionally, even minor inconsistencies in filament diameter along the spool can disrupt the flow, leading to gaps and weak spots in prints. Verifying filament diameter and compatibility with printer settings is crucial for maintaining print quality.

Extruder Calibration

Calibration problems in the extruder, such as misaligned or worn gears, can hinder its ability to grip and feed filament consistently. If the extruder tension is too tight or too loose, it may cause slipping or grinding of the filament, resulting in insufficient extrusion. Regular inspection and calibration of extruder components are necessary to secure optimal performance and prevent mechanical issues.

Software Settings

Improper slicer settings are a frequent but often overlooked cause of under-extrusion. If the flow rate is set too low, the printer will not push enough filament through the nozzle, leaving gaps and weak layers. 

Similarly, incorrect retraction settings can cause filaments to retract too far or too fast, leading to delays in extrusion during print restarts. 

Temperature Problems

Temperature plays a critical role in making sure of the smooth filament flow. If the nozzle temperature is too low, the filament may not melt properly, causing resistance and inconsistent extrusion. Over time, this can exacerbate clogging and lead to poor layer adhesion. 

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Troubleshooting 3D Printer Under Extrusion

Under-extrusion can derail even the most meticulously planned 3D print, leaving you with weak layers, gaps, or incomplete structures. The good news is that most under-extrusion issues can be resolved by systematically addressing the underlying causes. 

Try these essential steps to resolve under-extrusion for a smooth and reliable print:

Step 1: Check Filament Quality

Let’s begin with the simplest step: checking your filament. The quality and condition of your filament can significantly impact print performance. Budget filaments or improperly stored spools are prone to absorbing moisture, leading to brittleness, swelling, or inconsistent extrusion. 

Begin by ensuring the filament spool is not tangled or crossed, as knots or overlaps can create tension and restrict movement, leading to uneven or interrupted extrusion. Carefully unwind and rewind a portion of the filament to confirm it feeds smoothly without resistance.

Next, assess the filament’s quality and storage conditions. Filament that is brittle, swollen, or uneven in diameter can severely affect extrusion consistency. Exposure to humidity is a common culprit; moisture absorbed by the filament can cause it to swell, bubble, or weaken during printing, disrupting the flow through the extruder.

To maintain optimal filament quality, store it in a cool, dry, and airtight environment, ideally using resealable bags with desiccant packets to absorb moisture. Regularly inspect your filament before printing and discard any material showing signs of damage or degradation.

Step 2: Clean The Nozzle

Next is to clean the nozzle. A clogged or partially blocked nozzle is a frequent culprit of under-extrusion, as it disrupts the flow of melted filament during printing. The obstruction often results from residue left by previous prints, burnt filament fragments, or even dust particles that have entered the nozzle. 

To address this, begin by heating the nozzle to the recommended temperature for your current filament, which softens any residual material and makes it easier to remove. Use a cleaning needle to gently clear the nozzle opening or a soft wire brush to scrape away debris around the nozzle exterior.

For severe clogs, a cold pull is an effective solution. This process involves feeding cleaning filament or nylon through the heated nozzle, then allowing it to cool slightly before pulling it out, which dislodges hardened residue. Repeat the process if necessary until the nozzle is clean. If the clog persists despite these efforts, replacing the nozzle may be a quicker and more effective option.

Moreover, regular nozzle cleaning should become part of your maintenance routine, especially if you frequently change filament types, as different materials can leave varying residues that accumulate over time.

Step 3: Clean Gears, Motors, and Cooling Fan

Next is to check the cleanliness of your printer’s moving parts, such as extruder gears, motor, and cooling fan. This is essential for consistent performance and preventing under-extrusion, as over time, these components can accumulate dirt, dust, and filament debris, which reduces their efficiency and hinders proper filament feeding. Dirty gears can lose their grip on the filament, while clogged cooling fans may fail to prevent overheating, further exacerbating extrusion problems.

To clean these components, start with compressed air or a soft brush to remove loose dust and debris. Focus on the extruder gears, inspecting their teeth for any buildup of filament dust or grime.

Use a fine tool or a soft cloth to gently clean the gear teeth, ensuring that nothing obstructs the filament’s path. Neglecting this step can lead to slipping filament, inconsistent extrusion, and poor print quality.

Next, check the motor and cooling fan for dust or filament particles that might obstruct airflow or hinder movement. A clogged cooling fan can overheat the motor, leading to reduced torque and erratic filament feeding. Clean the fan blades carefully and ensure the airflow is unobstructed.

Step 4: Inspect the Bowden Tube

The Bowden tube plays a significant role in guiding filament from the extruder to the nozzle, but it can also be a hidden source of under-extrusion issues. Over time, the tube may develop bends, kinks, or internal friction points that restrict filament movement. Debris, such as filament dust or fragments, can also accumulate inside the tube, creating additional resistance. 

Inspect the tube closely for any visible damage or wear, especially near connection points where friction is most likely to occur. If you notice bends or excessive friction, consider replacing the tube with a new one. High-quality bowden tubes, such as those made with PTFE (polytetrafluoroethylene), are more resistant to friction and wear.

Next, consider applying a small amount of lubricant specifically designed for bowden systems. This can also help reduce resistance and ensure smooth filament feeding.

Step 5: Increase the Print Temperature

Next is addressing the print temperature, which plays an important role in achieving smooth filament flow. If your filament isn’t melting properly, it will struggle to pass through the nozzle, leading to under-extrusion. 

Begin by checking the recommended temperature range for your specific filament, as each material—PLA, ABS, PETG, etc.—has different melting characteristics. Increase the nozzle temperature in small increments of 5–10°C while running a test print, observing how the filament flows and adheres.

Be cautious not to exceed the filament’s upper temperature limit, as overheating can cause stringing, blobs, or even degrade the filament, leading to other print issues. Keep a close eye on the print’s surface quality and layer adhesion as you adjust the temperature.

Step 6: Adjust the Flow Rate

Next, let’s look at the flow rate, also referred to as the extrusion multiplier, which determines how much filament the printer pushes through the nozzle. If the setting is too low, your printer will under-deliver material, creating gaps, weak layers, or incomplete prints. Adjusting the flow rate can be done in your slicer software, where you can increase it in small increments, typically by 1-5% at a time.

As you make adjustments, observe the print results carefully. If the flow rate is increased too much, you risk over-extrusion, which can lead to thick layers, poor surface quality, or even filament jams. 

Remember, the goal is to achieve a balanced flow that provides sufficient material for strong layer bonding without creating excess. 

Step 7: Refine Retraction Settings

Next is refining the retraction settings, which play a key role in controlling filament movement during non-printing moves. 

Retraction is designed to pull the filament back slightly to prevent stringing and oozing, but overly aggressive settings can create problems. If the retraction distance is too long or the speed too fast, it may retract more filament than necessary, leaving insufficient material in the nozzle when printing resumes. This delay in extrusion can result in gaps or thin areas at the start of each new section.

To address this, open your slicer software and experiment with reducing the retraction distance and/or speed. Start with small adjustments, as even slight changes can have a significant impact. Next, test your new settings on a print with complex movements, such as one with multiple retractions, to ensure the changes effectively prevent gaps without causing stringing. 

Step 8: Adjust the Layer Height

After adjusting the retraction settings, the next step is to consider the layer height. Printing at a fine resolution requires your extruder to deliver very precise and consistent amounts of filament, which can amplify under-extrusion issues if the flow isn’t perfectly calibrated. 

If you’re experiencing gaps or weak layers with small layer heights, try increasing the height slightly, such as moving from 0.1mm to 0.15mm or 0.2mm, depending on your print requirements.

Start by increasing the layer height, which reduces the demand on the extruder by requiring less precision in filament delivery for each layer. This adjustment not only minimizes the risk of under-extrusion but can also improve print speed, as fewer layers are required to complete the object. 

Afterward, run test prints with the new layer height to ensure the balance between print quality and extrusion consistency meets your needs.

Step 9: Calibrate the Extruder

Next is calibrating the extruder. This is an essential step for ensuring your printer delivers the precise amount of filament needed for consistent prints. An improperly calibrated extruder can lead to under-extrusion because it may push less filament than required, resulting in gaps or weak layers. 

To check calibration, use a ruler or calipers to measure the actual length of filament the extruder feeds compared to the intended length. For example, if you command the extruder to feed 100mm of filament, but it only delivers 90mm, you’ll need to adjust the settings. In most printers, the extruder steps-per-millimeter (e-steps) value in the firmware or control panel determines how much filament is extruded for a given command. 

Calculate the new e-steps value based on your measurements and update it in your printer’s firmware or through the control interface. 

After making adjustments, run a test print to verify that the extrusion is accurate. Proper extruder calibration ensures consistent filament delivery, which is essential for reliable and high-quality prints.

Step 10: Update The Printer Firmware

Finally, one often overlooked yet essential step in resolving under-extrusion and improving overall print performance is checking your printer’s firmware. Firmware controls the core functions of your printer, including how the extruder operates, and outdated firmware may contain bugs or limitations that affect extrusion consistency. Manufacturers frequently release firmware updates to fix known issues, optimize performance, or add support for new features.

To update your firmware, visit the manufacturer’s website and locate the latest version for your printer model. Follow the provided instructions carefully, as updating firmware incorrectly can lead to errors or even render your printer temporarily unusable.

Fine-Tune Your Printer for Flawless Prints

Addressing under-extrusion is imperative to achieving reliable and high-quality 3D prints. Maintaining components like your extruder, nozzle, and filament is essential to ensure consistent filament flow and prevent common print defects. With the right adjustments and regular upkeep, you can eliminate under-extrusion and extend the lifespan of your 3D printer.

For more pointers, complete how-tos, and thorough printer reviews, stop by 3DGearZone, your top source for knowledge and tools to improve every aspect of your 3D printing experience. Whether you’re troubleshooting under-extrusion or picking out your next printer, we’re here to help you make the right decisions.

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