QuestionHow to fix 3d printer under extrusion

03/05/2026 10:34:06 Published

There’s nothing more disappointing for 3D printing hobbyists and professionals than investing time, filament, and effort into a print—only to pull it off the bed and find gaps between layers, thin fragile walls, or incomplete details. 3D printer under extrusion is one of the most common FDM (Fused Deposition Modeling) printer issues, and it’s defined by the printer failing to push out enough molten filament to create smooth, solid layers . The good news? Under extrusion is almost always fixable with simple adjustments, basic maintenance, or minor tweaks to your slicer settings—no advanced technical skills required.

In this comprehensive guide, we’ll break down how to identify 3D printer under extrusion, the most common causes (ordered by frequency), step-by-step fixes you can implement today, material-specific tips, and pro tricks to prevent under extrusion for good. By the end, you’ll be able to troubleshoot under extrusion quickly, save filament and time, and achieve consistent, high-quality 3D prints every time.

How to Identify 3D Printer Under Extrusion (Key Signs)

Before diving into fixes, it’s critical to confirm you’re dealing with under extrusion—since it’s often confused with other issues like layer shift or nozzle clogs. Here are the telltale signs to look for :

Gaps Between Layers: Visible spaces between horizontal layers, making the print look “gappy” or incomplete. This is the most obvious sign of under extrusion.
Thin, Fragile Walls: Print walls are thinner than your slicer settings (e.g., 0.8mm walls printing as 0.5mm) and easily breakable due to insufficient filament.
Rough, Uneven Surfaces: The outer surface of the print is bumpy, uneven, or has a “stringy” texture, with missing filament in key areas.
Underfilled Infill: Infill patterns (e.g., grid, honeycomb) are incomplete or sparse, even when set to a high percentage (e.g., 50%+).
Extruder Skipping: The extruder motor makes a “clicking” or “grinding” noise as it struggles to push filament—this means the motor is skipping steps because it can’t overcome resistance .
Inconsistent First Layer: The first layer has thin, patchy lines (instead of smooth, consistent lines) that don’t adhere well to the bed.

Pro Tip: To rule out other issues, print a simple test model (e.g., a 20x20x20mm cube) with default settings. If the cube has gaps or thin walls, you’re definitely dealing with under extrusion <superscript:4>.

Common Causes of 3D Printer Under Extrusion (By Priority)

Under extrusion almost always stems from one (or more) of these issues—most of which are easy to overlook. We’ve ordered them by how often they occur, so you can troubleshoot efficiently:

1. Clogged or Partially Clogged Nozzle

The #1 cause of under extrusion is a clogged or partially clogged nozzle. Over time, leftover filament, dust, or debris builds up inside the nozzle, restricting the flow of molten filament<superscript:3><superscript:6. This is especially common if you switch between filaments (e.g., PLA to PETG) without cleaning the nozzle, or if you print with low-quality filament that leaves residue. Even a tiny clog can drastically reduce filament flow <superscript:1>.

2. Incorrect Nozzle Temperature

Every 3D printing material has a specific optimal nozzle temperature range. If the temperature is too low, the filament won’t melt completely, making it too thick to flow smoothly through the nozzle <superscript:3><superscript:6. If it’s too high, the filament may soften too early (before reaching the nozzle), creating drag and reducing flow<superscript:3. Even a 5–10°C difference can cause significant under extrusion—especially for materials like PETG or ABS <superscript:2>.

3. Loose Extruder Gears or Insufficient Tension

The extruder uses gears to grip and push filament into the hotend. If these gears are loose, dirty, or worn, they’ll slip on the filament instead of pushing it consistently <superscript:4><superscript:6. Insufficient tension on the extruder idler (the wheel that presses filament against the drive gear) also causes slipping—look for filament with deep, uneven indentations or white dust (from worn filament) on the gears <superscript:4>.

4. Incorrect Slicer Settings

Slicer settings are a common culprit, especially if you’ve recently adjusted them. The most problematic settings include <superscript:1><superscript:6:

Flow Rate (Extrusion Multiplier): If the flow rate is set below 100% (e.g., 90%), the printer will extrude less filament than needed.
Filament Diameter: Most slicers default to 1.75mm filament—if you’re using 2.85mm filament (without adjusting the setting), the printer will under extrude.
Print Speed: Printing too fast overwhelms the extruder, preventing it from pushing enough filament to keep up with the print head <superscript:4><superscript:6.
Retraction Settings: Excessive retraction (too much distance or speed) can pull molten filament back into the hotend, creating a “gap” in flow when printing resumes <superscript:4><superscript:6.

5. Poor Filament Quality or Moisture

Low-quality filament with inconsistent diameter (e.g., varying from 1.70mm to 1.80mm) causes under extrusion, as the printer can’t adjust to the changing size <superscript:3><superscript:6. Moisture in filament (especially hygroscopic materials like PETG, ABS, or nylon) turns to steam during printing, creating bubbles and disrupting flow <superscript:4><superscript:5. You’ll often hear a “popping” sound when printing with moist filament.

6. Nozzle Too Close to the Bed

If your bed is unlevel or the Z-offset is set too low, the nozzle will be too close to the bed <superscript:1><superscript:3. This squishes the first layer too much, obstructing filament flow and causing under extrusion—especially in the first few layers <superscript:1><superscript:2. This is often mistaken for bed adhesion issues, but it’s actually a flow problem.

7. Hotend Cooling Issues

The hotend’s cooling fan is critical for controlling the “melting zone” of the filament <superscript:2><superscript:4. If the fan is broken, blocked, or set to the wrong speed, the filament may soften too early (above the nozzle), creating drag and reducing flow <superscript:2>. This often causes under extrusion that gets worse as the print progresses (e.g., first few layers are fine, then gaps appear).

8. E-Steps Calibration Issues

E-steps (extruder steps) determine how much filament the extruder pushes for each step of the motor. If your E-steps are not calibrated, the printer will extrude too little (or too much) filament—even if all other settings are correct <superscript:4><superscript:6. This is a common issue after replacing the extruder motor or hotend.

Step-by-Step Fixes for 3D Printer Under Extrusion

Follow these fixes in order (from easiest to most advanced) to resolve under extrusion quickly. Start with the first three steps—they fix 90% of under extrusion issues:

Step 1: Clean or Unclog the Nozzle

A clogged nozzle is the most common cause, so start here. Here are three effective methods to unclog or clean your nozzle:

Cold Pull (Best for Partial Clogs): Preheat the nozzle to your material’s printing temperature (e.g., 200°C for PLA), extrude a small amount of filament, then cool the nozzle to 90–120°C (PLA) or 140–160°C (PETG) <superscript:4<superscript:6. Grip the filament firmly and pull it out quickly—this will pull out any debris or hardened filament from inside the nozzle.
Needle Cleaning (For Small Clogs): Preheat the nozzle to 200°C, then use a thin nozzle cleaning needle to gently scrape out debris from the nozzle opening. Be careful not to damage the nozzle <superscript:3>.
Replace the Nozzle (For Severe Clogs): If cleaning doesn’t work, replace the nozzle—they’re affordable (usually $5–$15) and often faster than repeated cleaning <superscript:6. For specialty nozzles (e.g., hardened steel), ensure you’re using the correct temperature (5–10°C higher than brass nozzles) <superscript:1<superscript:2.

Pro Tip: After cleaning or replacing the nozzle, print a test cube to verify flow is restored <superscript:4.

Step 2: Adjust the Nozzle Temperature

Set your nozzle temperature to match your filament—this is critical for smooth flow. Use these guidelines (adjust ±5–10°C based on your printer and filament brand) <superscript:5<superscript:6:

PLA: 190–215°C (most common: 200–205°C). If under extrusion persists, increase by 5–10°C <superscript:4.
PETG: 230–250°C (most common: 235–240°C). PETG needs higher temperatures to flow smoothly <superscript:5<superscript:6.
ABS/ASA: 230–260°C (most common: 240–250°C). Use a closed enclosure to maintain consistent temperature <superscript:5.
TPU: 210–230°C (most common: 220°C). Print slow (15–30mm/s) to avoid flow issues <superscript:5.

Pro Tip: If you’re unsure, start with the higher end of the temperature range—this helps melt the filament fully and clear minor clogs <superscript:6.

Step 3: Tighten and Clean Extruder Gears

Loose or dirty extruder gears cause slipping, which leads to under extrusion. Here’s how to fix them:

Clean the Gears: Use a small brush or toothpick to remove filament dust, debris, or leftover filament from the extruder gears <superscript:4<superscript:6. Pay special attention to the teeth of the drive gear—this is where filament slips most often.
Adjust Tension: Locate the extruder idler tension screw (usually on the side of the extruder). Turn it clockwise to increase tension—you want the idler to press firmly against the filament, but not so hard that it crushes or wears the filament <superscript:4<superscript:6. Test by pulling the filament gently—you should feel resistance, but it shouldn’t be impossible to pull.
Inspect for Wear: If the gears are worn (e.g., teeth are rounded or broken), replace them—worn gears can’t grip filament properly <superscript:4.

Step 4: Adjust Slicer Settings

Incorrect slicer settings are a common fix—here’s what to check (using Cura, PrusaSlicer, or your preferred slicer) <superscript:1<superscript:6:

Flow Rate (Extrusion Multiplier): Set it to 100% (default). If under extrusion persists, increase by 5–10% (e.g., 105–110%) and test. Avoid setting it above 115%—this can cause over extrusion.
Filament Diameter: Confirm it matches your filament (1.75mm is standard; 2.85mm is less common). Even a 0.05mm difference can cause under extrusion.
Print Speed: Reduce your overall print speed by 20–30% (e.g., from 60mm/s to 40–45mm/s). For complex models or small details, slow down to 30–35mm/s <superscript:4<superscript:6.
Retraction Settings: Reduce retraction distance and speed. For direct-drive extruders, use 0.6–1.5mm retraction distance and 20–35mm/s speed <superscript:4<superscript:6. For Bowden extruders, use 3–6mm distance and 30–45mm/s speed. If retraction is too high, it pulls filament back into the hotend, causing gaps.

Step 5: Dry or Replace Filament

Moist or low-quality filament causes under extrusion—here’s how to fix it:

Dry Filament: For hygroscopic materials (PETG, ABS, nylon), use a filament dryer or place the filament in an oven at 40–60°C for 4–6 hours to remove moisture <superscript:4<superscript:5. Store filament in a dry box with desiccant to prevent reabsorption.
Replace Low-Quality Filament: If your filament has inconsistent diameter (check with calipers) or leaves residue, switch to a high-quality brand. Look for filament with a consistent diameter (±0.03mm) <superscript:3<superscript:6.
Check for Tangles: Ensure the filament spool is not tangled—tangles create resistance, making it hard for the extruder to push filament <superscript:4<superscript:6.

Step 6: Adjust Bed Level and Z-Offset

A nozzle that’s too close to the bed obstructs filament flow. Fix it with these steps <superscript:1<superscript:3:

Level the Bed: Preheat the bed to your material’s temperature, then use the paper test to level it—slide a piece of paper between the nozzle and bed; you should feel slight resistance <superscript:1<superscript:2.
Adjust Z-Offset: If the bed is level but the nozzle is still too close, increase the Z-offset (move the nozzle away from the bed). Print a first-layer test to ensure the lines are smooth and consistent, not squished.

Step 7: Fix Hotend Cooling

Poor hotend cooling causes filament to soften too early—here’s how to fix it<superscript:2<superscript:4:

Check the Cooling Fan: Ensure the hotend fan is working (spin it gently to confirm it’s not stuck). Clean any dust or debris blocking the fan blades.
Adjust Fan Speed: For PLA, use 100% fan speed after the first layer; for PETG and ABS, use 30–50% fan speed (too much cooling can cause flow issues) <superscript:5.
Inspect the Heat Break: Ensure the heat break (the part between the hotend and extruder) is properly installed— a loose or bent heat break can cause uneven cooling <superscript:2.

Step 8: Calibrate E-Steps

If all other fixes fail, calibrate your E-steps to ensure the extruder pushes the correct amount of filament <superscript:4<superscript:6:

Mark the filament 120mm from the extruder entrance (use a marker or tape).
Use your printer’s control panel or G-code to extrude 100mm of filament.
Measure the remaining distance from the mark to the extruder entrance. If it’s more than 20mm (e.g., 25mm), the extruder is under extruding—you need to increase E-steps.
Calculate the new E-steps using this formula: New E-steps = (Current E-steps × 100) / (120 – Measured Distance).
Update the E-steps in your printer’s firmware and test again.

Material-Specific Tips to Fix Under Extrusion

Different materials have unique flow needs—tailor your approach with these tips <superscript:5<superscript:6:

PLA (Polylactic Acid)

PLA is the easiest material to print with, but it’s prone to clogs if temperatures are too low. Use a nozzle temperature of 200–215°C, print speed of 40–60mm/s, and 100% fan speed after the first layer. Avoid over-tightening extruder gears (PLA is brittle and can break).

PETG (Polyethylene Terephthalate Glycol)

PETG is hygroscopic (absorbs moisture) and needs higher temperatures to flow. Dry PETG for 4–6 hours before printing, use a nozzle temperature of 235–250°C, and reduce print speed to 30–40mm/s for perimeters. Use 30–50% fan speed to prevent cooling-related flow issues.

ABS (Acrylonitrile Butadiene Styrene)

ABS requires a closed enclosure to maintain consistent temperature. Use a nozzle temperature of 240–250°C, bed temperature of 100–110°C, and print speed of 40–60mm/s. Avoid excessive retraction (3–5mm for Bowden extruders) to prevent flow gaps.

TPU (Thermoplastic Polyurethane)

TPU is flexible and can cause extruder slipping. Use a nozzle temperature of 220°C, print speed of 15–30mm/s, and disable retraction (or use 1–3mm for direct-drive extruders). Increase extruder tension slightly to grip the flexible filament.

Pro Tricks to Prevent Under Extrusion Long-Term

Once you’ve fixed the immediate issue, use these tips to avoid under extrusion in future prints:

Regular Maintenance: Clean the nozzle and extruder gears every 1–2 weeks, or after switching filaments <superscript:4<superscript:6. Lubricate the extruder mechanism to ensure smooth movement.
Use High-Quality Filament: Stick to reputable brands with consistent diameter—this reduces clogs and flow issues <superscript:3<superscript:6.
Store Filament Properly: Keep hygroscopic filaments (PETG, ABS, nylon) in a dry box with desiccant. For PLA, store in a cool, dry place <superscript:4<superscript:5.
Test Prints: Print a small test model (e.g., a single-wall cylinder) before starting large prints to verify flow<superscript:4.
Avoid Over-Retraction: Use the minimum retraction needed to prevent stringing—excessive retraction is a common cause of under extrusion <superscript:4<superscript:6.
Check Nozzle Size: For filaments with additives (e.g., wood, carbon fiber), use a 0.6mm or larger nozzle—smaller nozzles (0.4mm) can clog easily <superscript:2.

Troubleshooting: When Nothing Else Works

If you’ve tried all the above and still have under extrusion, check these final fixes:

Worn Hotend Components: If the heat break or throat is worn or damaged, replace them—they can restrict filament flow <superscript:2<superscript:6.
Extruder Motor Issues: A weak or faulty extruder motor may not have enough power to push filament. Test the motor by manually extruding—if it struggles or skips steps, replace the motor.
Firmware Glitches: Restart your printer and re-slice your model. Sometimes, corrupted firmware or slicer files cause under extrusion<superscript:4.

Final Thoughts: Mastering Under Extrusion Troubleshooting

3D printer under extrusion is a frustrating issue, but it’s also one of the easiest to fix once you know the causes. Start with the simplest fixes—cleaning the nozzle, adjusting temperature, and tightening extruder gears—and work your way up to more advanced tweaks like E-steps calibration.

Remember: Every printer and filament combination is unique. Don’t be afraid to experiment with settings (e.g., increasing temperature by 5°C or reducing speed by 10mm/s) to find what works for your setup. With a little patience and these tips, you’ll be achieving smooth, consistent, and high-quality 3D prints in no time.

Happy printing!

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