How to fix under-extrusion

In its simplest form, under-extrusion is when the printer is unable to supply the right amount of material. You’ll know if your printer is under-extruding as you’ll see missing layers, very thin layers, or layers that have random dots and holes in them. This problem is probably the trickiest to find the direct cause as there are so many variables to consider, but we’ll take you through them here and give you helpful pointers to remedy it.

How to fix under extrusion

Ultimaker robot shows signs of under-extrusion

Note: If your print is just missing a single layer in the print, this is not under-extrusion. In this case there’s a ‘skipped layer’ problem, as described here.

Material and material settings

The first and easiest things to check if your print is suffering from under-extrusion are the material settings. It’s important that the material profile on your Ultimaker (or material settings in Cura) matches the material. For example, a temperature setting that’s either too high or too low can lead to problems. When the temperature is too low, the material won’t melt properly as cooler plastic is more viscous and requires higher pressures to push it through the nozzle. Eventually, the pressures will simply become too high and under-extrusion happens. On the other hand, when the temperature’s too high, it can cause problems as the properties of the material will start to change if left in the nozzle for too long, causing clogs. Please check your filament spool for the proper temperatures.

Closely related to the temperature are the nozzle size, the print speed, and layer height. These settings define the flow rate, which is the volume of material that is extruded per second. If you want to push through more material than your Ultimaker is capable of, this will lead to under-extrusion. There should always be a good balance between the temperature and speed. At higher temperatures, you can print faster, but when printing at lower temperatures you might have to decrease the speed to get a proper extrusion.

Besides material settings, it’s also possible that the material itself is causing the problem. For example, the filament can sometimes get tangled after removing it from the 3D printer – this is where it gets stuck before entering the feeder. Therefore it’s always a good idea to check that the filament isn’t overlapping on the spool before you start printing.

Another reason can be the absorption of too much moisture by the filament. Some materials (especially PVA) are very sensitive to moisture and can loose quality when used or stored in a humid environment for too long. Correct handling and storage of the material is very important in this case. For the optimal conditions for your materials, we recommend to take a look at the material guides.

The feeder

The feeder is the part of an Ultimaker that literally ‘feeds’ material into the 3D printer and is, therefore, the first component that could cause extrusion problems. A few symptoms that could indicate your feeder is causing under-extrusion:

  • The material is hardly moving towards the hot-end
  • Material grinds in the feeder
  • The feeder is ticking back/skipping
Feeder of the Ultimaker 2+
The Ultimaker 2+ feeder

When the material doesn’t move through the bowden tube and hot-end properly, it could mean there’s friction in the bowden tube or hot-end, or that the feeder doesn’t have enough grip on the material. In the latter case, the feeder tension could be too low. This can easily be diagnosed by taking the material out of the 3D printer and checking if there are visible marks on the material. If the material is completely smooth, it means the feeder tension is too low.

Good feeder tension
Marks on material means good feeder tension ✔
Too low feeder tension
No marks on material means too low feeder tension ❌
Too high feeder tension
Grinding of the material means too high feeder tension ❌

Contrary to this, it can also be that there’s too much tension on the feeder. When this happens, the material is basically being ‘squeezed’ in the feeder, causing it to flatten and can’t be pushed further. Consequently, the feeder will dig into the material and ‘eat it away’. This is called grinding. Additionally, the feeder could also start making a ticking sound or skip back. Grinding and skipping can also occur when there’s a blockage in the hot-end, but this will be described in more detail later on in this guide. When your filament is ground down, it’s important to remove the material from the Ultimaker, clean the feeder and check the feeder tension before continuing. For a more detailed explanation on how to do this, you can take a look at this page.

The bowden tube

Once the material has passed the feeder, it will be forwarded through the bowden tube. It’s possible the material could actually experience friction in the bowden tube, leading to under-extrusion. There are a few possible reasons for this friction.

When the filament has been ground down, there’s a good chance that small particles from this ‘grinding’ have entered the bowden tube. These particles can cause friction in the bowden tube and eventually lead to under-extrusion. That’s why it’s best practice to check the bowden tube is clean if filament has been ground down inside it.

Friction in the bowden tube can also be caused by the filament on the spool. Towards the end of the spool, the coils are usually small and tight. When going through the bowden tube the filament will experience higher friction than if the filament was nice and straight. If you’re printing at the limit of what the printer can achieve, this additional friction can be enough to cause problems with your print.

The hot end

From time to time, you may experience under-extrusion due to a problem with the printer’s hot-end.

The Ultimaker 2 hot end
Ultimaker 2 hot end

First of all, there could be a partial blockage in the nozzle, stopping the filament from running through properly. Such a blockage is often caused by some dirt or carbonized material in the hot-end. There are several ways of clearing this; therefore please take a look at this page that describes how to unclog a nozzle.

For all Ultimaker 3D printers except the Ultimaker 3 (Extended) another common reason for under-extrusion, especially after many hours of printing, is a deformed coupler. This is the white part in the hot end, which is called the PTFE coupler for the Ultimaker 2 Family and Ultimaker Original(+) and TFM coupler for Ultimaker 2+ printers. The coupler is a consumable item that wears over time and slowly changes shape on the inside due to heat and pressure in the hot-end. Eventually, this will cause friction to the material that has to pass through and causes under-extrusion. To check if the coupler in your hot-end is deformed, and instructions on how to replace it, you can take a look here.

The Ultimaker coupler wears over time
New vs. worn coupler

A third hot-end related cause for under-extrusion could be a bad adjustment of the hot end itself (for example after you’ve replaced it). It’s important that parts fit well together so that there’s no distance in-between them. If the parts haven’t been placed correctly, there’s a chance that material will leak in-between them and eventually cause clogs in the hot-end. Take a look at the page about the hot-end adjustment for more detailed information on this.