New filament "not moving as expected"  

Ian Bebbington
New Member


I recently purchased some "PETG HDGlass Transparent Green" filament (from Devil Printers but which was shipped directly from CEL - I won't be using Devil Printers again!). Unfortunately I've yet to have a successful print with this filament. Every time I try to use it I get the dreaded "filament not moving as expected" error. I've done the usual cutting back the filament to non-marked material and squaring it off to no avail.

Once purged, I can print successfully with my other filaments so think this filament must be faulty. Is this likely to be the case or might there be an issue with my Robox?



Posted : 31st May 2019 9:49 am
Topic Tags
I am Pete Admin

@ibebbs if you have some calipers (even cheap ones are really handy) please try measuring the diameter of the filament, check it several times along a few meters. Also check it is round by measuring twice in the same place but rotating the filament 90°.

It would also be good to test if the material is passing through the tubes and other parts easily without the head attached.

  1. Eject all filament.
  2. Power off <always do this when you fit or remove the head>.
  3. Remove the head.
  4. Power on.
  5. Feed the problem filament in.
  6. Use the controls to feed it so it passes all the way out past where the head would be feed it backwards and forwards a bit and see if there is any sign of extruder skipping. A chug chug chug sound.
  7. Eject again then power off before fitting the head.

Report to the service portal if it doen't improve.

For official support please create a support ticket using this link

Posted : 31st May 2019 2:36 pm
Ian Bebbington
New Member

Hi Pete,


Thanks for the reply. I finally got a chance to do some measurements and can confirm that, over the first three metres, the diameter of the filament remains fairly consistent (and round) at about 1.75mm +/- 0.03mm. I trust this shouldn't be an issue for the Robox?

I don't believe - but am open to being wrong - that there's an issue with the Robox itself given I am able to print successfully with other filaments.

Please let me know if you think it's worth reporting to the service portal or whether I should be looking to return the filament as damaged.

Thanks, Ian

Posted : 7th June 2019 12:05 pm
Estimable Member

PETGs can saturate with humidity from the surrounding air if they are not stored in an airtight bag or container with silica gel. The humidity in the filament expands into steam at a volumetric rate of 1000 to 1 inside the extruder. This can give you all kinds of trouble from clogging feed pipes, excessive oozing, inconsistent material flow rate to bad layer adhesion and ugly prints.

Dry out your PETG filament for two weeks in an airtight bag with a pound of fresh oven baked silica gel. It is best to keep the rolls of filament in an airtight bag or container during printing. PETGs need to be bone dry to print properly.

Posted : 10th June 2019 7:33 am
I am Pete Admin

What are you other filaments?

PETG is a big harder than ABS and doesn't flow quite as easily.

The hardness will effect how it can be gripped by the extruder gears.

Does it skip during purging?

You could heat the nozzles, open the valve and feed the filament using the buttons, these buttons have speed controls and should not skip (g0 commands do not have speed controls so might show skipping anyway).

While it is feeding through the nozzles listen for little pops and look for evidence of bubbles in the extruded material. Take care of the hot nozzles!

Bubbles and popping sounds will indicate wet filament which is harder to extrude.

This post was modified 4 months ago by Pete

For official support please create a support ticket using this link

Posted : 10th June 2019 11:02 am

This community page and the content inside is publicly visible except in restricted groups. A registered community member is able to post content. Because of the open nature of this forum the content posted may not represent the views of CEL. While we do regularly read the content posted, in some cases the content may not be appropriate for the reader or may cause offence. Please help us by reporting such content. Technical advice provided in this forum may be provided with good intention and a belief that is is correct but may not be applicable to all hardware, software or user ability. In some cases content may not be relevant to newer or older revisions, conflicting or incorrect advice may be contained within conversations, community moderators will attempt to add to this or make corrections but to preserve the thread this may be on following pages or be missed as the forum evolves.

For official advice users should contact the CEL support team via and follow the provided advice to preserve safety, warranty and function of Robox hardware or software.
This applies to any use or alteration which is not specifically described in the officially supplied guides from CEL. Community content should not be considered official even where posted by CEL employees. Only advice provided via the CEL support portal should be considered official.
Robox is a complex machine with many potential uses, to help preserve the good working order of both hardware and software please be patient and note that many common fixes for other 3D printers do not apply to Robox and may cause irreversible damage or compromise safe operation.