How to Fix Under Extrusion- What Causes Under Extrusion on Your 3d Prints and How to Fix Them

3D printing is considered to be efficient, cost-effective, and highly customizable. However, as powerful as things manufacturing technique is, it does come with a few flaws and challengers. Without resolving them and finding solutions as soon as you encounter them, you’ll have trouble achieving the results you’re looking for.

Keep in mind that the reason why 3D printing pros have so much experience in technical troubleshooting and improvisation is that so many things can go wrong during the 3D printing process. Furthermore, few problems require just one solution. So as a 3D printing enthusiast you need to get used to doing research and performing small adjustments.

Under-extrusion is one of these problems, but fortunately, it’s one of the easier ones to solve. It isn’t difficult to notice a printed object that didn’t end up as intended due to under-extrusion. For instance, you may spot random holes, a few missing layers, or at least layers that are too thin. In other words, a print that suffered from under-extrusion looks plain awful. In addition, the structure of the print is also severely weakened.

With that being said, we have to ask ourselves: what is under-extrusion, and what causes it? How can we change the settings to fix this serious problem? Let’s find out!

Understanding Under-Extrusion

As you can probably guess from the name, under-extrusion occurs when the hot nozzle doesn’t extrude as much filament material as needed. An object that’s printed with less material than required will contain empty spots inside the layer or miss a layer altogether. You need to learn how to spot the problem and accurately diagnose it. But that’s the easy part. Fixing the problem is more complicated, but not too difficult even if you’re just starting out in the world of 3D printing. So, why and when does under-extrusion occur?

The filament spool is stuck:

The filament material can easily get stuck if it wasn’t wound up correctly. But the 3D printer can also cause this issue if it fails to roll the filament thread correctly. When that happens, the spool will often get stuck and in turn cause so much friction that the motor fails to correctly grip the material when it's being fed to the printer. The result is less material going in or in other words, under extrusion.

The extruder is clogged:

Sometimes when we aren’t careful we’ll notice filament leftovers clogging the head of the extruder. When that happens any new filament material we feed through the extruder will cause additional friction. This friction is troublesome enough to slow the speed at which the material goes to the nozzle, and therefore we get to experience under-extrusion.

However, clogging can also occur inside the feeder motor. So make sure that the motor cog that’s responsible for feeding the filament through the nozzle doesn’t contain any material that doesn’t belong there.

The nozzle is clogged:

You need to clean the printer’s nozzle every now and then to keep it in perfect working condition. Filament material can gradually build up and in time it will clog the hole. When that happens, you won’t be able to admire a successful print anymore. A blocked nozzle is one of the most common causes of under-extrusion, so make sure you inspect it and test it. You can do that by pushing the filament by yourself and see how well it passes through the nozzle. If you feel some kind of resistance, or worse the material doesn’t go through at all, then you’re dealing with a clogged nozzle and you have to clean it.

Deformed or bent Teflon tubes:

Some printers use Teflon tubes to unroll the material and push the filament through the print head. If any of the tubes become deformed, there will be more friction applied to the filament. When that happens, there’s too much pressure on the motors of the feeder and that’s what causes the under-extrusion. Take note that Teflon tubes can be warped by overheating due to the printer emitting too much heat. Another common cause is a lack of printer maintenance, especially when using the machine frequently.

The printing temperature is too low:

You always need to pay attention to the printing temperature. If it’s too low while printing fast, you’ll end up with under-extrusion because the flow rate of the material is far greater than the required temperature. The material simply doesn’t melt quickly enough for it to be correctly fed through the nozzle.

Not enough pressure on the material feeder:

Usually, FDM 3D printers enable us to modify the material feeder’s pressure settings. The right pressure is crucial for controlling the amount of force the motor applies to the filament in order to establish a strong grip. If the pressure is too low, that grip is lost and we get to experience another case of under extrusion. Fortunately, the pressure level can be checked. All you need to do is hold the material when the motor is working and if you feel that the grip is being lost and the material slips, you need to increase the pressure.

With that in mind, you also need to verify and adjust the pressure whenever you change the filament. Make sure to check the manufacturer’s recommendations based on the filament’s diameter.

The printing speed is set too high:

Printing an object too fast is another leading cause of under-extrusion. It’s extremely important for the flow rate of the material to match print speed. If the speed is higher than the flow rate, you won’t have enough filament going through the nozzle. If that happens, make sure to lower the speed in small increments until it matches the flow speed.

How to fix the under-extrusion problem?

As you can see, a lot of things can go wrong and cause under-extrusion. While the problem itself isn’t all that complex, it’s challenging because you have to verify so many possible causes. For the 3D printer to work properly, we need to perfectly balance the extruder, hot end, and the printing head so that they work in perfect unison to create the best piece. Anything that goes wrong and ruins the balance between these three elements will throw off your results. To prevent that from happening, or to fix your under-extrusion problem if you already have it, you need to take a number of investigative steps and make adjustments to the printer’s settings.

Inspect the printer and the materials

• Inspect the filament diameter: This is the first thing you should check. Far too many people make this obvious mistake, including the pros, so don’t feel bad about it. For example, if you’re using a filament that is 3mm in diameter, but the slicer is set for a 1,5mm filament, the extruder won’t operate at the correct rate. Even when there’s a smaller variation between the two diameters you can end up with under-extrusion. So, first of all, make sure you buy good-quality filament from a reputable manufacturer or distributor. If that’s out of the way, take a caliper to verify the filament’s diameter. Make sure its value matches the diameter setting on the slicer.
• Inspect the Teflon tubes Since most printers use Teflon tubes due to the materials’ friction reduction characteristics, you need to make sure that they’re perfectly smooth and undamaged. As mentioned earlier, they need to have a perfect path between the filament and the extruder to work correctly. The problem is that these tubes get easily damaged, either due to a lack of maintenance, high temperatures, or because you’re printing a lot. Even when the tubes are just slightly damaged, that’s enough to lead to under-extrusion. So if you spot any problems with the Teflon tube, throw it away and replace it with a brand new one. There’s nothing you can really do to fix it. The other solution is to simply print your project without it.
• Inspect the filament spool: Sometimes the filament gets stuck. The spool needs to be tightened just right to make sure the material is steadily fed into the extruder. However, if you tightened it too much, it’s likely to get stuck sooner or later. When that happens, there’s too much friction inside the feeder and that will cause under-extrusion. If you encounter this problem often, you should start winding the filament by hand and make sure it doesn’t overlap anywhere. The filament has to flow without any interruptions or snags.
• Inspect the nozzle: If none of the above solutions solve your under-extrusion problem, there might be an issue with the nozzle. As mentioned earlier, the nozzle can sometimes get clogged. Luckily, you can unclog it without much difficulty. You don’t have to disassemble it. All you need for starters is a pin. Try to unblock the nozzle by sticking a pin to remove whatever is clogging it. If that doesn’t, then you’ll have to resort to removing the nozzle and cleaning it properly. Chances are you have some filament stuck inside it, so place the nozzle in acetone. If everything fails, it’s time to say your goodbyes and buy a new nozzle.
• Inspect the extruder idler: When something goes wrong with the extruder itself, you’ll have to disassemble it. There’s no shortcut around it. Nearly every single time we’re dealing with a faulty extruder we’re going to also deal with under-extrusion. So if this is your first time doing this, take a deep breath and pay attention to each step you take because you’ll have to reassemble it again. Take notes or pictures if you have to.

Normally, the extruder is made out of two important components that push the filament to do the nozzle, namely the drive gear and the idler. While the purpose of the gear is to grip the material it can’t do that without a frictionless surface. This is where the idler comes in, allowing the gear to hold the filament against it. This means that there’s a lot of friction for the idle to handle and that force is constant throughout the printing process. As you can imagine, the idler will gradually wear down. When that happens, the extruder can no longer grip the filament. That’s how we get under-extrusion. So make sure to check the idler. As long as you know how a brand new idler is supposed to look like, you’ll be able to identify a worn out idler. If that’s indeed the problem, the solution is to buy a new one.

• Inspect the drive gear: As mentioned, the extruder is mainly made out of an idler and a drive gear. The gear is pushed by the stepper motor. Its teeth are used to grip the material and hold it against the frictionless surface provided by the idler. The filament is pushed gradually towards the hot end nozzle. What can happen here is the gear getting clogged. Sometimes material gets stuck between the gear’s teeth, preventing it from gripping the material further. As you can imagine, this results in under-extrusion. Fortunately, cleaning that drive gear is a simple process. The challenging part is reassembling the extruder once you're done.

Check the settings and adjust them

If you finished inspecting and adjusting the printer’s components and materials and you’re still dealing with the under-extrusion problem, the root of the cause may lie in the printer’s settings.

• Pay attention to the printing temperature: If the temperature doesn’t perfectly match the printing speed, the filament may not melt properly. This will obviously lead to extrusion problems. So check the temperature setting and make sure it matches the filament you’re using.

On the other hand, if the temperature is set higher than the filament’s requirements, you’ll have another problem on your hands. Each plastic reacts in a certain way at set temperatures. If you go beyond their melting point, you may weaken its structure or degrade it in some way. So always make sure you are within the recommended temperature margins.

• Inspect the feeder and monitor it: The first mechanism that pushes the material is the feeder, and you guessed it! The feeder can also cause under-extrusion. Pay attention to it and if you notice that it’s not pushing the filament as it should, you probably need to increase its pressure. However, if you’re uncertain, don’t increase the pressure too much or you’ll end up with a flat filament and a much slower feeding speed.
• Fine-tune the extrusion multiplier: Sometimes the extruder itself doesn’t feed the filament fast enough. If that’s the case, you need to increase the extrusion multiplier. Do it gradually, around 2% at a time, otherwise, you might speed things up to the point of causing a blockage. Furthermore, remember that when you increase the speed you need to increase the temperature as well, or you’ll end up with under-extrusion once again, but this time because of low temperatures.

Final thoughts

As you can see, a lot of things can cause under-extrusion. Whether you’re a beginner or a pro, sooner or later you’ll have to deal with it. When the time comes, go through the checklist. Check one possible cause at a time. Don’t rush through the troubleshooting process or you’ll end up working a lot more than you should. And who knows, maybe you’ll discover new causes or solutions and share them with your fellow 3D printing enthusiasts.