3D printing: Under extrusion and how to resolve it

Under-extrusion often shows up as a strange texture on the outside of the print, as if there are a lot of holes in the shell. The print will also feel lighter than it looks as there is not as much plastic put in the print as there should have been. The problem can come from many places, so follow the guide below and try them out and see which solution works for you.

I have a new printer or slicer profile

Extrusion multiplier

With a new printer and/or a new slicer profile (saved slicer settings), there may be settings that need to be corrected to avoid under-extrusion. The slicer must know how much filament it must press through to keep the hotend fed during the print. It is a good place to start to get rid of under-extrusion. The setting for the different slicers can be found at;

  • SimplyPrint slicer: Outside > Shell print factor
  • Cura: Custom > Material > Tandhjulet > Flow > Checkboks > Close > Material > Flow
  • Simplify3D: Edit process settings > Extruder > Extrusion multiplier
  • Prusa slicer: Print settings > Advanced mode > Filament settings > Extrusion multiplier

Set the value up by 0.1 and run a test print to see if it gets better. Continue experimenting with the setting until the texture disappears. When you are above 1.5, something else is probably wrong and you can try to follow the solutions below.

The problem has arisen out of the blue

Print speed

Different printers have different limits on how fast they can print without encountering problems. Many printers are limited by how much filament the extruder can push through in a given amount of time. Try lowering the print speed setting in your slicer and run a test print. If this does not resolve the issue, try the following solutions. The print speed setting for the different slicers can be found at;

  • SimplyPrint slicer: Filament > Print speed
  • Cura: Custom > Speed > Print speed
  • Simplify3D: Edit process settings > Speeds > Default printing speed
  • Prusa slicer: Print settings > Advanced mode > speed > Perimeters

Tighten the extrusion

If your printer's extruder is not tensioned well enough, it can quickly end up slipping on the filament instead of pushing it down into the hotend. This makes it difficult for the extruder to keep the pressure in the hotend up and will result in under extruding. Many extruders have a way of tightening and releasing the pressure that is applied to the filament towards the gear that drives it forward, often by compressing a spring with a screw.

Cold pull

The first place you can see signs of a clogged nozzle is in the filling. Due to the slightly higher speeds, there is higher pressure in the hotend which has difficulty getting out if something is stuck in the nozzle.

It's a good idea to clean the nozzle with a cold pull which is performed by heating the nozzle up to the print temperature of the material mounted on the printer. When hot, push some filament through before setting the printer to cool. When it reaches 50 degrees, the heat can be turned on again and then pull on the filament until it releases from the hotend and takes impurities out of there. Do the same 2-3 times more to be safe. For best results, use filament such as nylon or PETG for this as they are a bit more slippery than standard PLA.

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Published: Oct 2020, updated: Mar 2021