The pictures explain my problem. I have already tried to reduce the retraction but that showed no effect. Thank you for your help.

The effect is a total stop of the print (no material is extruded).

  • Creality CR 10
  • Cura 3.4.1

I recently added this new feeder aluminium block because the 3D printed stock version was bad quality.

Filament not entering Bowden tube

Close up

  • $\begingroup$ Can you also add what does work, what changed since your last good print, etc. $\endgroup$ – Sean Houlihane Sep 14 '18 at 17:58
  • $\begingroup$ Does it seem to anyone else that the teeth marks are excessive in the filament, as if the tension idler force is set too high? $\endgroup$ – fred_dot_u Sep 14 '18 at 21:35
  • $\begingroup$ I've always run my extruders at max pressure and haven't seen any issues related to it. $\endgroup$ – tjb1 Sep 15 '18 at 2:03
  • $\begingroup$ What printer is this? and is the hotend running? $\endgroup$ – Trish Sep 15 '18 at 7:44
  • $\begingroup$ @Trish It is a Creality CR 10. The hotend is running. Usually the raft is printed without any problems but afterwards the filament starts to fail. $\endgroup$ – DonaldEnte Sep 15 '18 at 8:55

This is typically caused by resistance in the tube or hotend but in your case it appears to be mostly caused by a very poorly designed extruder. The filament needs to be constrained closer to the drive gear. You may be able to drill out the PTC connector to allow the PTFE tube to reach closer to the gears or print a spacer to fit in between but you need to support the filament in that gap.

You can try raising the hotend temperature as a band-aid until you can fix the problem, do not exceed 240 C if you have a PTFE lined hotend. Long retractions can also pull molten filament into the cold zone where it solidifies and make extrusion harder.

As an example, here is a picture of a Bondtech BMG extruder. Note how the extruder constrains the filament path all the way from the drive gear to the hotend entrance. While this example is extreme for normal PLA/PETG/ABS, it is required for flexible filament. A 4mm gap (or closer) should be fine for PLA/PETG/ABS or other hard filaments.

enter image description here

  • $\begingroup$ Thank you very much. I just installed that "upgrade" extruder (aluminium) and I'll try switching back to the stock version. $\endgroup$ – DonaldEnte Sep 15 '18 at 9:08

Your extruder is encountering resistance and the filament path is too open.

Your teeth seem to be biting in too hard. Loosen up your tensioners a bit. Teeth biting too hard deforms the filament. Does that rough looking stuff feed through the tube smoothly? Any rough bits can catch anything in the filament path?

It is preferable for the motor to skip when there is a problem, rather than waste filament, so maybe turn down your motor vref too.

How well does filament feed by hand, and with no teeth marks on it? Significantly better, or about the same? Does the bowden tube have and kinks or bends in it? Those effectively shrink the diameter of the tube and really put the squeeze on filament passing through.

Does your hotend have proper thermal preparation? Lots of insulation on the block, and a good strong cooling fan? Too little insulation will cause too much power to be used, and raise the melt area. Too little cooling (especially with PLA) will also allow the melt area to rise (called heat creep). If pointing a big fan at the printer fixes the problem, it's probably hotend cooling related. If it makes it worse, it's hotend insulation related.

  • $\begingroup$ The bowden tube is perfectly new as well as the whole hotend (it works perfectly) . I will try the difference of feeding with and without teeth marks. Thank you for your help :) $\endgroup$ – DonaldEnte Sep 15 '18 at 9:10

There are two parts to this problem.

First, the extruder is meeting too much resistance in the print. There can be several causes, from the first layer being too low, a blocked nozzle, too low a print temperature, or printing too fast, so the viscosity of the filament just makes it too hard to pass through the nozzle. Usually, several of these will be in play together.

Second, the extruder design allows the filament to bend as it leaves the drive gears. Typically, this problem is seen most with flexible filament because that will obviously collapse more easily under compression for a given unsupported length.

The trigger is the first group, the second part determines the resiliance of your setup to this problem. Once the break point is reached, there is no recovery. You can retract the filament, but trying to resume the print will just set the extruder back to the same absolute position.

First, check that you can extrude OK in free space, without any drop in temperature. Also check your extrusion steps calibration - if you're extruding 110% of what the print is expecting, the extrusion back pressure can build up to a point of failure. Check the first layer, check the calibration.


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