3D Printer Under-Extrusion – Causes and Fixes

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How to Fix 3D Printing Under Extrusion

At 3DSourced we’ve covered everything 3D printing and 3D since 2017. Our team has interviewed the most innovative 3D printing experts, tested and reviewed more than 20 of the most popular 3D printers and 3D scanners to give our honest recommendations, and written more than 500 3D printing guides over the last 5 years.

Under-extrusion in 3D printing occurs when the printer’s nozzle can’t dispense enough filament, leading to incomplete or weak prints.

You’ll notice under-extrusion as missing print layers, layers that have gaps and holes, or prints that have a thin, spongy feeling.

Your under-extrusion problem is likely to be either a mechanical issue, a problem with your filament, or a case of using the wrong print settings.

In this guide, I’ll share my simple solutions to fix under-extrusion issues from years of hands-on experience to help get your 3D printer running smoothly again.

A typical example of under-extrusion
A typical example of under-extrusion

Under-extrusion Diagnosis Checklist

Potential ProblemSymptoms
Feeder IssuesFilament slipping or grinding, causing it to not extrude quickly enough.
Clogged NozzleThe filament isn’t extruding correctly or not at all. Uneven or thin layers.
Loose PartsYour printer fails to function smoothly, with erratic movement, unusual noises and unexpected shutdowns.
Filament IssuesInconsistent extrusion producing brittle prints and causing nozzle clogs.
Incorrect Print TemperaturePoor surface quality, weak surface adhesion, warping or curling.
Incorrect Retraction SettingsSigns of under-extrusion at the start of printing layers or after travel moves.
Incorrect Printing SpeedPoor layer adhesion, uneven layers, or filament isn’t extruding correctly as the printer is moving too fast.
Poorly Leveled Printer BedThe filament is not sticking to the bed correctly. First-layer problems such as uneven extrusion or scraping against the bed.
Under extrusion problems
Every 3D printer’ users worst nightmare, waking up to this after an overnight print.

Mechanical Issues

Feeder Problems and Solutions

Your feeder is responsible for pulling the correct amount filament from the spool and guiding it into the hot end for extrusion.

Filament under extruded
Look familiar? Your feeder gear might have too much pressure, or simply slipping on the filament instead of feeding it.

Incorrect Feeder Tension Settings

Using the wrong feeder tension settings can lead to under-extrusion.

If your tension is too low the filament will slip, meaning there is not enough grip for the filament to be pulled through the extruder.

Similarly, too-high tension settings will cause the filament to grind in the feeder, slow down and under-extrude.

Solution: Adjust the feeder tension settings to the right level. Many newer feeders have a built-in tension indicator – but if yours does not, you can use the steps below.

  1. First, loosen the tension screw to the point where the filament does not pull at all.
  2. Now begin to tighten the tension screw until the filament pulls smoothly.
  3. If the filament begins to grind and make a “ticking” sound, you’ve tightened too much.

You can also check this YouTube video for a full walk-through for checking and fixing your tension settings.

Feeder Maintenance Issues

Under-extrusion can also be caused by filament debris building up over time in the feeder. This debris reduces the feeder’s grip on the filament, meaning less is extruded overall.

Solution: Regularly cleaning your feeder will prevent filament particle buildup (and the risk of under-extrusion).

Consider using cleaning filament between your prints, or check your 3D printer’s user manual for recommended cleaning guidelines.

Filament debris is more common if you’re not using a filament type compatible with your extruder.

For example, if you use a high-temperature filament such as PEEK in a hobbyist 3D printer designed for ABS or PLA filament, the printer’s hot end won’t reach the necessary temperatures and will under-extrude.

Check my complete best 3D printer filament guide to ensure you’re using an appropriate material.

Bowden Tube Issues

Clogs in the Bowden Tube

Clogs in your bowden tube can cause under-extrusion by increasing the friction on your filament, making it more difficult to push filament through.

Solution: To clean your bowden tube, remove the collet clip, press down on the collet around the PTFE tube, and pull the tube with a firm tug, checking for clogged filament and deteriorated PTFE tubing.

We have our full guide to fixing filament stuck in PTFE tubing, or you can see the process in action on an Ender 3 in this video walkthrough:

Damaged Bowden Tube

under extrusion from Bowden tube issue

Under-extrusion can also be the result of a damaged Bowden tube causing friction and preventing the filament from passing through smoothly.

Solution: Regularly inspect the inside of the tube for scratches or other types of damage, and replace if required.

I recommend checking and replacing Bowden tubes after about a year to avoid under-extrusion problems.

Here’s a video walkthrough from The Nerdy Review:

Preventing and Fixing Clogged Nozzles

Nozzle clogging is a common cause of under-extrusion. Clogging happens when filament residue builds up and blocks the nozzle, limiting the flow of filament.

The results of a clogged nozzle
This is the sort of under-extrusion a clogged nozzle causes

Clogging is more common with poor-quality third-party materials that don’t melt evenly. 

You should check our full guide to clogged nozzle fixes – but here’s the TL;DR:

a clogged nozzle

How to Clear Clogged Nozzles

  • Reverse feed the print material out of the print head.
  • Heat the print head to approximately 260°C
  • Carefully insert a long, thin needle (slightly smaller than the nozzle diameter) into the nozzle, gently moving it in and out to clear the blockage. Check nozzle is clear.
Unblocking that nozzle

To see this method in action, check the video from Make With Tech:

If That Doesn’t Work, try a Cold Pull

For more stubborn nozzle blockages, you may need to use the more powerful “Cold Pull” technique (also known as the “Atomic Method”).

  1. Remove the Filament: Pull any excess filament out of the print head. Remove the clamp holding the Bowden tube to the print head and detach the tube gently.
  2. Heat the Print Head: Heat the print head to the filament’s recommended printing temperature. Meanwhile, cut about 20cm from the filament spool and straighten it as much as possible.
  3. Insert the Cut Material: Carefully insert the cut piece of material into the print head, applying pressure until it extrudes from the nozzle or can’t be inserted further.
  4. Cool Down: Lower the print head temperature to 60°C. Any clog or dirt in the nozzle will bind to your new filament
  5. Pull: Once the print head has cooled, quickly and cleanly pull the material out of the print head.

3D Printing Nerd has a clear and trustworthy guide below:

Structural Issues

Loose Parts

Under-extrusion can also occur when your 3D printer parts have become loose over time. A clicking or knocking sound is often a sign that something isn’t quite tight enough!

Solution: Regularly inspect your 3D printer to ensure that all the parts are tight and properly connected.

Hold your 3D printer frame and give it a light shake to check for that feels loose or wobbly.

Some of the most common culprits are extruder gears, the screws on your hotend, and the eccentric nuts securing the z-axis.

Faulty Electrical Connections

An unstable power supply to your hot end can cause under-extrusion by failing to properly heat your filament, limiting the rate at which it flows through the extruder.

Solution: Check all electrical elements, including wires and connectors, to ensure they are securely connected and undamaged.

See the clip below for exactly the sort of thing I’m talking about.

Debris in Moving Parts

Under-extrusion can also occur when a part is prevented from moving smoothly, causing a mismatch between your slicer’s expectations of what is happening and the reality of your print.

The most common issue is a build up of debris within the tracks of the 3D printer gantry your hot end uses to travel.

When the extruder travels unpredictably, it can cause under-extrusion in sections of your print because the hot end is not where it “expects” to be.

Solution: Use a wire brush to clean moving parts and remove any filament or other debris that has built up over time.

Cooling Fan Issues

If your cooling fan isn’t functioning properly, you won’t be able to achieve the right print temperature. This could increase your flow rate and cause a nozzle blockage, leading to under-extrusion.

The ability of your filament to flow properly is intrinsically linked to achieving the right print temperature.

Filament Obstruction in the Fan

If something is blocking your fan, it is not going to be able to rotate properly and lower your print temperature.

Solution: Regularly check and clean the front fan of the printer and remove any strands of filament that may have become stuck between the fan blades. I recommend checking every three months.

Cooling Fan Not Working at All

In some cases, your cooling fan may have simply lost efficiency over time and need replacing altogether.

Solution: Manually increase the nozzle temperature to 60ÂşC or higher and check if the cooling fan is spinning. At this temperature, the fan should have kicked to life, and if not, the fan may need to be replaced.

Check this clip for more detailed cooling fan troubleshooting:

Damaged PTFE Coupler

A PTFE coupler prevents your bowden tube from moving around during retractions – but it can also be a cause of under-extrusion.

Think of the PTFE coupler as a small tube or tunnel the filament travels through. Sometimes, this small tube can get misshapen or squashed over time, due to heat and pressure.

Because of this blockage, less filament can get to the heater block to get melted and then printed, resulting in under-extrusion.

To confirm if the PTFE coupler is damaged, disassemble the print head and inspect the coupler. Look for brown or burned areas where it touches the nozzle. Check the channel from the bottom up and ensure it is a straight cylindrical hole without any bulges.

Solution: Replace your PTFE coupler with your own printed part. For improved reliability, use heat-resistant filament like polycarbonate and consider adding a metal spacer.

Filament Issues

Under-extrusion can also be affected by the quality, type, diameter, and storage conditions of your filament.

In general, before adjusting settings on your printer, always check your filament first.

Wrong Filament Diameter

Under-extrusion will occur if the diameter settings on your slicer doesn’t match the actual filament, because your 3D printer will anticipate more filament is being extruded than there actually is.

Most filaments come in two main sizes (1.75mm or 2.85mm), but cheaper or off-brand filaments may have inconsistencies in diameter.

Solution: Ensure you set the correct diameter in your slicer software to match the actual diameter of your filament.

If you’re using Cura, check your “Compatible Material Diameter” setting is correct.

Filament diamater settings in Cura
Filament diameter settings in Cura

Filament Knots

Knots or tangles in your filament can cause the filament to get stuck or grind in the printer and result in under-extrusion.

tangled filament
An example of tangled filament

Solution: Carefully unwind the filament past the knot and spool it back up. Using a filament clip to secure the filament can help prevent knots and tangles in the future.

You can check our guide to reviving your tangled filament to save you from just throwing it away.

Poor Material Storage

Poor storage of your filament will cause it to degrade over time, affecting its density and diameter. This can lead to under-extrusion because your slicer cannot accurately anticipate the amount of filament it extruding.

Solution: Keeping your filament dry is key to avoid it degrading. Use a proper filament box to maintain the correct humidity and out of direct sunlight.

Similarly, wet filament will also cause irregularities in your prints. If that happens, check our guide on how to dry your filament.

Wrong Slicer Settings

Low Flow Rate

Flow rate describes how quickly filament is pushed through the nozzle over a given period. Under-extrusion occurs when your flow rate is set too low.

Flow rate is affected by many factors, which can make it a little tricky to diagnose. Print speed, print temperature, and retraction settings all come into play.

Print speed is the speed at which the nozzle moves while extruding filament. Under-extrusion occurs when the print speed is too high and the extruder does not have time to properly heat and push out enough material.

Solution:

  1. Start with the filament manufacturer’s recommended speed settings and assess the quality of your prints on this test run.
  2. Then, you can make adjustments from there in 5mm/s increments.
  3. If you notice an improvement you can continue in that direction; and if not, go back the other way until you find the sweet spot for your 3D printer and chosen filament.
Print speed settings in Cura
Print speed settings in Cura

You can check our full guide to the best 3D printer speed settings to make sure you’re on the right track.

Wrong Print Temperature

When your extruder temperature is too low, the filament doesn’t melt properly and moves less freely, lowering your flow rate and causing under-extrusion.

Similarly, higher temperatures can cause an excess of molten filament that turns into a blockage and causes under-extrusion.

Solution:

  1. Test and Observe: Print a test object or use a temperature tower to assess how your filament melts at different temperatures.
  2. Gradually Adjust Temperature: Adjust the print temperature in increments of 5°C until you find the right temperature for your specific filament and printer combination. 
  3. Find the Right Temperature: Keep in mind that your 3D printer’s thermal sensors may be slightly inaccurate, causing a disparity between your print settings and the manufacturer-recommended temperature.
Temperature settings in Cura
Temperature settings in Cura

Retraction Settings – Distance Too High

You may need to adjust your retraction settings if you’re experiencing under-extrusion issues in specific areas of your prints like corners or seams.

When the retraction distance is too high it causes a delay in the filament being pushed forward for extrusion, meaning not enough filament will be extruded overall.

Intermittent under extrusion caused by improper retraction settings
An example of intermittent under-extrusion caused by improper retraction settings

Solution: Troubleshoot with these steps

  1. Lower Retraction Distance: Reduce the retraction distance by 1 mm at a time. 
  2. Increase Retraction Speed: Gradually increase the retraction speed by 5 mm/s at a time. 
  3. Observe Print Quality: While adjusting the retraction settings, closely monitor the print quality. Stop adjusting when the under-extrusion issue disappears or becomes negligible.

If you start experiencing stringing or blobs, you’ve gone too far and will need to raise your retraction distance again.

Incorrect Bed Leveling – Nozzle Too Close To Bed

If your printer’s bed is not leveled correctly, it can lead to under-extrusion, especially on the first layer.

This is because your slicer software needs a level surface to accurately predict the Z distance (distance between the nozzle and build surface), and if the nozzle is too close to the bed, your filament won’t be able to extrude properly.

under-extrusion caused by improper bed levelling
Under-extrusion caused by improper bed leveling. Notice that the bottom side is trying and straight, while the top is thin and flimsy.

Solution: Ensure you properly level your printer’s bed by using first-layer calibration:

  1. Clean the 3D printer bed with Isopropyl Alcohol to remove any excess filament.
  2. Preheat the printer to its operating temperature.
  3. Set the printer to the home position (0,0,0).
  4. Look for an option on your printer controls titled “Bed Leveling“, “Level Corners” or “Bed Tramming”. 
  5. This will begin a calibration process and move the nozzle to key locations across the bed. Using a piece of paper as a gauge, adjust the height of the nozzle at each corner and the center.
  6. Load and run a bed-level test print.
  7. Assess the print results.
    • If the nozzle is too close to the bed, it will cause a rough, uneven surface.
    • If the nozzle is too far, there will be gaps between the filament lines.
    • If the nozzle distance is right, the lines will be slightly flattened and blend well.

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