I made a post in Dutch about causes for airprinting: a stopping and stuttering extruder.

Hereby the translation in English. Maybe others have some additional observations and thoughts.

Eventually it happened to everyone: the printing stops halfway and the extruder is only printing air. Sometimes it happens that there is only discontinuously printed. The extruder fails for a moment and then continues. That gives interrupted print lines as shown here.
Airprinting and stuttering Extruder

However, a very different reason is when only spaghetti is printed. The extruder works just fine, but the print lines attach no more then a printer creates full of spaghetti. That problem will not be discussed here.
Airprinting and stuttering Extruder

There are several reasons for when an extruder isn't extruding anymore, while the head is still moving on the bed as if nothing is happening.

Concerning the terms used. There is a distinction between the 'hotend' of the extruder: it is the lower part of nozzle, the heater block and the "barrel" above. The 'coldend' part is the part of the extruder where the filament is driven: so the steppermotor, the drive wheel, the clamping mechanism and the holder on which everything is attached.

It is first useful to look at what actually is happening at the extruder. There are several possibilities:

  • The drive wheel turns and seems to jump with a clunck, clunck, clunck sound. It is very likely the hotend or Nozzle clogged.
  • The drive wheel is running continuously, and the filament is, as it were "shaved". Probably the drive wheel is full of plastic and there is a hole visible in the filament after removal. Both the supply of the filament can be blocked, as well the hotend blocked.
  • The drive wheel is not moving, but the motor shaft turns . Then, the drive wheel is loose and needs to be fastened again by fastening the socket screw / grub screw to the axis of the motor. Note that the Allen screw is sitting on the flat part of the shaft.
  • The drive wheel and the motor stand still while printing. Very unlikely, but that happens when the wiring, steppermotor or stepper driver are broken. However, a loose contact is likely, check both the connector of the motor as well the connector on the PCB. This is located on the back of the printer: You have to unscrew the rear panel. Do not yank it immediately, because the connector to the fan must be taken apart first.


Possible causes of the first two problems, some are listed in order of difficulty and the best to see as a checklist:

Checklist Printer, Mechanics.

1. tangled filament

If the filament spindle is not carefully handled, it may be that there is a loop or knot formed on the spool which is getting tangled. Ultimately, the friction is that the the extruder is shaving or skipping. Also, a spindle which is unwound next to the reel or is askew to the filament holder can have this effect. A simple solution for that, see here.

2. The handle on the extruder is open.

Then the clamp to the filament is not sufficient and no traction is possible.

3. The drive wheel is flooded with plastic particles or damaged

The drive wheel can be cleaned with a brush or a toothpick for example. We also use such a small brass brush that comes with a Dremel. If eea really is flooded, then disconnect the drive wheel and with -for example- a stanley knife clean between the teeth. When using metal-or carbon filled filament, the drive wheel can be very quickly wear out. Optionally, the wheel can be slightly moved on the shaft of the motor, so it's using an undamaged part of the drive wheel. After that, the drive wheel must be replaced. When using normal filament however,the drive wheel won't wear that fast. The drive wheel has to be fastened by means of the socket screw to the axis of the motor. Note that the Allen screw is sitting on the flat part of the shaft.

4. Loose parts hinder the smooth transit / extruder fan is not running

In particular, the two buses where the flexible hose is in between (ie those between the filament spindle and the extruder) can come off and sit askew. In extreme cases, the hotend is slightly loose, or the entire extruder motor unit. Not likely though. It may also be that the fan is not running. Loose contact or damaged wiring.

5. Clogged hotend, simplest solution.

Always check, for any action whatsoever: heating the extruder manually and by the LCD panel reverse remove the filament. It is best to heat the extruder slightly more than normal. So for example PLA to 230 degrees instead of 215. If the extruder is not able to get the filament out (and thus skips or shaves), the filament can be hand pulled. It is best not break, but firstly increase the temperature of the extruder until the filament can be smoothly pulled out, because it's melted in the extruder again. Then enter a fresh piece of filament (the first 10 centimeter cut so) and enter again into the extruder / hotend as normal. 9 times out of 10 this is sufficient.

6. Clogged hotend solution with some insistence.

If you are unable to enter into new filament after the above measurements, then the filament presumably has been too hot somewhere in the hotend and cooled thereafter. Thereby causing a hard plug. In order to solve this problem: increasing the temperature of the extruder even more, for example to 250 degrees and from above in the hollow screw of the hotend poking with the smallest Allen key which is supplied. It may take a while for the temperature sufficiently has climbed "up" to melt the plug again. If necessary, the fan unit can also be removed to make the temperature in the upper hotend to climb even more. When that is done, it is important to keep constant poke / push until the plug is melted and can be pushed down. Then immediately reinstall the fan unit.

After this it's very likely that filament can be processed as normally.

7. Clogged Nozzle

When all that solutions hasn't had the wanted effect, or if there was no clogging in the hotend itself, the nozzle itself can be blocked. Dust particles or hardened filament can clog the nozzle. The only solution is to take it off, and burn it clean with a torch. Or replace it with a new one. Halfway through this post is how it can be done.

8. Clogged hotend, the rigorous solution.

It may be that the hotend is that much polluted that all the above solutions have not worked. Then this post shows how to clean the complete hotend. It is also possible to replace the hotend as a unit.

Checklist Slicer Settings.

The above problems often have a mechanical cause, but a number of which can also be caused by slicersettings. Some are listed below:

  • A too low printing temperature: the filament does not melt sufficiently, or not fast enough or at high speeds.
  • Too high printing temperature: the temperature climbs too much in the hotend and will be soft there and nod, a clog having as a result.
  • Extremely low speeds, combined with a high temperature, see above.
  • Broken extruder fan (loose contact) or a closed printer with little ventilation, so the room temperature is too high. See above.
  • Too high speeds with a large layer height (possibly combined with high or low temperature extruder). The flow may be too large for the corresponding filament. Then reduce printing speed considerably. This is usually the cause of stuttering print lines.
  • The bed is not properly calibrated, and the nozzle is too close to the bed, so that the pressure is too high in the extuder so it's skipping and/or is shaving filament.
  • Over extruding, so also at higher layers the pressure in the Nozzle is too high, because of the extruder is not able to spit out the demanded amount of filament. Happened especially with solid parts, so at loops and a massive infill. The filament diameter has to be increased in the slicer.
  • Excessively use of destringing. So if there are many small travel distances then almost the same spot of the filament will be shaved because of the driving wheel is doing a rapid up and down movement each time. Then best reduce the printing speed itself, maybe reducing the retraction speed as well, and/or set a smaller retraction distance and above all increase the minimum distance where a retraction has to be done.
  • Exotic print materials as Woodlay and metal cored filaments contain particles that can clog the extruder.

Specifically for stuttering print lines: Out of the above-mentioned possibilities (an excessive speed and thus flow is moreover most likely) it is most likely that the driving wheel is partly polluted and thus hasn't intermittent not have any grip on the filament .


November 25, 2015

Bartaar Bartaar
Service partner
1664 posts

2 replies

Sometimes you have a jam but not a clog. Common with PLA, in this scenario the part of filament inside the hotend expands and makes a plug. You should reverse the extrusion, shave the plug off, reinsert the filament and purge.
Causes can be bad extruder ventilation, wrong temperature for specific filament fabrication... and so on.
I managed changing the fan (on a modified CB that uses a E3D hotend). The next try (if this fails) would be canola oil on the filament.

November 25, 2015

Angelo Venosa Angelo Venosa
267 posts

Some great info Bart, thanks!

November 25, 2015

Matthew L Matthew L
703 posts
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