3D printing under extrusion is one form of inconsistent extrusion (the other being over extrusion). Unfortunately, it can have a myriad of causes. No 3D printer troubleshooting guide would be complete without the full list of causes.
Here’s an attempt to classify and list possible reasons and fixes. We also have a dedicated article on under extrusion issues here.
Signs of under extrusion
The signs are easy to spot: you end up with weak prints that crumble, crack or tear under even slight stress, you have visible gaps in your objects, walls start becoming see through because solid areas show spongy patches instead.
Explanation:
Your prints are sticking too much and are hard to remove. You already tried [Under extrusion occurs when your printer is unable to supply the correct amount of material needed to correctly print a layer.
How to fix:
Under extrusion in general
Make sure your filament can unspool freely from the reel.
Check the filament path for any blockages or areas of strong friction.
Verify the filament diameter is consistent. Especially very cheap filaments suffer from fluctuations in filament diameter. Too thin and there isn’t enough filament fed into the HotEnd, too thick and there might be too much friction to push through the extruder and the related filament path.
Check the extrusion settings in your slicer, namely filament diameter, extrusion multiplier.
Check proper print temperature and speed. Try printing hotter and slower.
Also see [filament not feeding properly].
If you printer is constantly under extruding, as in: it is not pushing enough plastic, it is best to recalibrate the steps/mm value of your extruder to ensure your extruder delivers the proper amount of filament requested. Once the steps per mm are set correctly, the next step to a proper calibration is to set your extrusion multiplier (also called feed rate) properly. Both steps/mm as well as extrusion multipliers are filament dependent and might even change over time.
Or it could simply be a matter of you having changed the extrusion multiplier for a recent print and forgot to reset it in your slicer. Also, very often the root cause for constant under-extrusion is a partially clogged nozzle. Cleaning out your nozzle would be a good start. Also check [filament not feeding properly].
3D printer not extruding mid-print
You’ve come back to find your 3D printer not printing anymore. This along with coming back to find a ‘birdsnest’ are the two most cliche versions of failed 3D prints. For some reason or another, your 3D printer stops extruding mid print:
Filament has stripped or is blocked in the extruder. See [Clogged Nozzle]
Filament is kinked, snapped or ran out. The filament has twisted or you got a knot on the reel. See our article How to untangle a tangled spool
Filament diameter isn’t consistent. Especially very cheap filaments suffer from fluctuations in filament diameter. Too thin and there isn’t enough filament fed into the HotEnd, to thick and there might be too much friction to push it in through the extruder and the related filament path.
You’re trying to print a part with too aggressive retraction 3D printing settings or excessive amount of retractions in a short period of time. Check your 3D printer retraction settings and lower total amount of retractions occurring and/or reduce retraction distance. Sometimes loosening the feeder gear idler pressure onto the filament can help.
Overheated stepper drivers. A lot of tinkerers like to increase the Vref of their stepper drivers, often needlessly. This could lead to overheated steppers. Also, when printing high temperature filaments in an enclosed or heated build chamber steppers tend to get considerably hotter.
Nozzle clogged mid print. This again can have a lot of different causes. See [Clogged Nozzle]
If it happens very early in the print, it might be too much back pressure because the nozzle is too close to the bed. See [Nozzle too close].
In general: Try printing hotter or slower. But do not exceed the maximum print temperature of the filament, as it might start to deteriorate in your nozzle and clog. Very common error is to boil rigid ink PLA by exceeding the maximum print temperature.
Check for warping. Warped areas are closer to the nozzle increasing back pressure. See [Warping]
Monitor nozzle temperature while printing, check for high drops in print temperature.
Keep your nozzle clean, especially after switching between different filament types.
When using particle filled filaments, consider using a bigger nozzle.
Flexible filament got stuck. Flexible filaments are difficult to print with most extruders out there, as they tend to escape the intended filament path and simply get stuck. Try printing way slower, try printing hotter (within the recommended range) and maybe even consider upgrading to a different extruder design specialised in printing flexible filaments.
Also see [Filament not feeding properly].
Under extrusion at the beginning of a print
Under extrusion at the beginning of a print is common and to a point to be considered normal. It can take a bit to get the flow of filament going, this is where using a skirt if no brim is required comes in handy.
Consider using a skirt as this will show how consistently the material is being laid down before you waste filament on the printed object itself
Modify your start code in your slicer to add some extra priming. While you’re checking the codes, make sure you don’t have an excessive retract in your end code.
Often, not extruding properly at the beginning of a print is a result of the nozzle being too close to the bed or issues mentioned in the sections above.
Check print temperature, you might be printing too cold.
Also see [filament not feeding properly].
Under extrusion after retraction
During a 3D printing retraction, especially with very aggressive retract settings, there could be not enough filament in the nozzle to properly start the print again at the end of the travel move.
To fix:
Lower your retraction length.
Give it a bit extra restart distance to prime the nozzle after the retraction.
A series of very fast retracts can chew up a filament so that the feeder gear can slip on the damaged filament once you start extruding again.
To fix:
Slow down the retraction speed.
Check that the feeder pinch wheel tension is correct.