3D Printer Under-Extrusion: 8 Easy Fixes

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Gaps in a 3D printed helmet caused by 3D PRINTER UNDER-EXTRUSION

3D printer under-extrusion occurs when the printer’s nozzle doesn’t dispense enough filament. Under-extrusion can manifest in various ways, including missing print layers, gaps, and holes in the print.

Under-extrusion compromises print quality and strength.

You can solve under-extrusion by tinkering with your slicer settings and calibrating your 3D printer.

Let’s explore seven easy ways to fix 3D printer under extrusion.

What is 3D Printer Under-Extrusion?

A photo of a 3D print with areas of under-extrusion circled in red

3D printer under-extrusion occurs when your printer’s nozzle doesn’t release enough filament to complete a layer properly. If you notice gaps or holes, you may have an under-extrusion issue.

Under-extrusion leads to thin and brittle parts, affecting your printed object’s overall appearance and structural integrity.

Clogs, incorrect slicer profiles, hardware issues, or lack of maintenance can cause 3D printer under-extrusion.

If the issue begins suddenly, it’s best to look at your machine’s hardware before changing your slicer settings.

How to Fix Under-Extrusion

Check Your Filament

A dual color polymaker polyterra roll of filament left on the 3d printer

Incorrect filament diameter can cause under-extrusion. If you set the wrong filament width in your slicer settings, your printer will extrude less material than required.

For example, suppose you set your slicer to print with a filament diameter of 3 mm but actually use a filament with a 1.75 mm diameter. In that case, your printer won’t feed enough filament through the extruder. The lack of filament creates under-extrusion issues in the final print.

You can find the filament diameter on the filament’s box, on the side of the roll, or manually check the diameter using calipers.

 If you’re using Cura, you can update the filament diameter by visiting “Settings > Printer > Manage Printers > Machine Settings.”

Low-quality filaments can be the cause of print defects.

A 3d printed pikachu with print imperfections like stringing, zits, and blobs caused by wet filament
You can see gaps around the nose of this model caused by under-extrusion issues.

Cheap and low-quality filaments may have inconsistent diameters throughout the filament roll. The inconsistencies in width produce inconsistent extrusion.

Inconsistencies are less common now, as manufacturers have improved the manufacturing of 3D printing materials. The best 3D printing filaments have a dimensional accuracy of +/- 0.05 mm or less.

An inaccuracy of as little as +/- 0.1 mm can cause printing issues.

Additionally, tangles and knots in your filament spool can cause issues while your printer feeds filament to the hot end. Check your filament for kinks to prevent the material from getting stuck in the printer.

Using a filament clip, you can minimize the chances of knots and tangles. 

Even with careful handling, tangles are inevitable.

If you find a tangle or knot in your filament spool, pause the print and carefully unwind your filament past the knot. Be very careful to spool it back up without creating new tangles.

Finally, it’s important to ensure you’re printing with dry filament. Wet filament can cause issues like 3D printer stringing, zits, blobs, gaps, and holes in your 3D prints.

Wet filament is the culprit if you hear hissing or popping sounds while your printer is running.

You can dry out your wet filament in a filament dryer or dehydrator and continue to use it for future projects.

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It’s important to properly store your 3D filament in a cool, dry place to keep our filament dry and prevent it from absorbing moisture.

Clean the Nozzle

White filament oozing from the nozzle of an FDM 3D printer

A clogged nozzle can cause under-extrusion by restricting the flow of filament. Regularly cleaning your nozzle is an essential aspect of 3D printer maintenance to prevent buildup and maintain consistent extrusion.

Over time, molten plastic can build up inside the printer’s nozzle, preventing the hot end from extruding the required amount of filament.

Most of the time, you can clean the nozzle to remove partial clogs.

Follow these steps to clean your 3D printer’s nozzle:

  1. Pre-heat your printer’s nozzle to regular printing temperature.
  2. Use a needle or other fine object and carefully clean out debris from the nozzle.

In cases of significant filament buildup, you may need to remove the nozzle to clean out the old filament. You can also do a cold pull to remove unwanted filament buildup inside the print head.

If you can’t clean your nozzle, it may be time to replace it.

Check Your Extruder’s Gears

The gear box on an anycubic vyper 3d printer

Uncleaned and worn extruder gears can impact filament feeding, resulting in under-extrusion. Examine the extruder’s gears for signs of wear, debris, or damage.

The extruder motor uses gears to feed filament through a Bowden tube or directly to a direct drive extruder. As the gears feed filament into your machine, the gear’s teeth can remove small amounts of plastic from the filament, which clogs the mechanism.

Remove any debris and check for broken parts and worn teeth.

The gear’s teeth wear down over time. If necessary, replace worn or broken parts to ensure smooth filament feeding.

Increase Print Temperature

Four models being printed on an anycubic vyper 3d printer in dual color blue and red filament

The filament won’t melt properly if the print temperature is too low, leading to poor extrusion. Gradually increase the printing temperature in 5 to 10-degree increments while monitoring the print quality.

PLA generally works best at around 200 – 220°C. ABS and PETG print well at printing temperatures of 220-250 °C. 

Different filament brands, colors, and material types have different optimal printing temperatures.

If you’re noticing under-extrusion after switching filaments, your print temperature is a likely culprit.

Pro Tip: You can save time by printing a temperature tower. The temperature tower test print creates a stack of bridges at varying hot end temperatures.

The temperature tower allows you to test several nozzle temperatures simultaneously, quickly determining the best printing temperature for your filament type.

Adjust Filament Retraction

Adjusting your retraction settings can correct under-extrusion if you notice gaps along the seams and corners of your print. Gaps in direction changes may indicate that your filament is retracting too quickly or too soon.

Lower your retraction distance in increments of 1 mm and increase your retraction speed in 5 mm/s increments.

Run a test print after each change. If you begin to notice stringing or blobs, you’ve adjusted your retraction settings too far. An indication that your printing issue isn’t caused by the retraction settings.

Increase Flow Rate

White filament oozing from the nozzle of an FDM 3D printer

Try increasing the flow rate in your slicer settings, which causes more filament to extrude during printing. Increasing the flow rate can help balance any under-extrusion issues you may be experiencing.

 Increase the flow rate by 2.5% until you fix the extrusion problem.

Avoid increasing the flow rate above 110% (1.1 in Cura). You may create new issues like clogs and jams in the nozzle if you set the flow rate too high.

Additionally, you can calibrate the filament feeding by checking out this guide to set your extruder steps.

Lower The Print Speed

If your print speed is too fast, the printer won’t have enough time to deposit material, resulting in under-extrusion.

Every printer has different printing speeds. Most hobby-level 3D printers, like the Ender 3, can comfortably print at 60-100 mm/s. In contrast, Core XY printers have printing speeds of up to 500 mm/s.

Printing speeds are not commonly a culprit for under-extrusion. But you should consider lowering your print speed if the other fixes on our list don’t solve your problem.

If All Else Fails, Upgrade Your Extruder

If you have attempted all the above fixes and still experience under-extrusion, consider an upgrade to a higher-quality extruder. A better extruder can provide more consistent filament flow and help eliminate under-extrusion issues.

Replacing your printer’s hot end is a last resort. It’s costly and requires some t

Mario De Lio
Mario De Lio

Mario is a Mechanical Engineer with experience working at one of the largest industrial printing companies in the country. He previously owned a rapid prototyping company specializing in designing mechanical parts for 3D printing applications.

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