Random under extrusion

Hey Guys,I'm experiencing random under extrusion on my CR-10s which then results in a blocked nozzle. When the block occurs, with the nozzle at 200c I can easily pull out the filament, and then feed it back in and continue to manually push the filament through without feeling unusual resistance.

I thought this may have been heat creep, as it occurs randomly, so I replaced the stock hotend with a genuine E3d V6, which with the machine being 2 years old I thought it was a worthwhile replacement/upgrade. I have upgraded my firmware to the latest Marlin version, taken from the Creality website, and run PID tuning.

This happens with any filament I use, whether this is cheap amazon esun filament (~£15 per kg), ProtoPasta premium, or Polyalchemy Elixir. I have tried each filament at temps of 200, 205 and 210.By randomly, this could happen almost straight away and lay down a rubbish first layer, or wait until 5hrs into the print then start missing layers. Sometimes it starts extruding normally again rather than completely blocking.

One thing I have noticed is that if I print a temperature test, the small details appear to over extrude and the nozzle digs itself into the layers it has already printed, so that the conical shape ends up warped. This might be a separate problem which I can worry about later.

Changing the nozzle worked for a large print, then the issue re-occurred. I'm wondering if the cheap filament could be leaving debris in the nozzle?I've been tinkering for over 2 weeks now and am running out of ideas! The most confusing part is that the new E3D V6 is showing exactly the same issues as when I had the stock extruder on.

Attachment 14116Attachment 14117

Here are some pictures to show a more succesful print, the problem is usually more extreme than this

As food for thought, it might be time to change the PTFE tubing, and take apart the extruder gears and give them a clean out.

However also double check you Z height dimensions are correct, if the Z axis is slipping at points the layer is more squished and the filament cant flow correctly and the pressure builds up and the filament can't extrude enough, and can cause blockages in the throat. Alternatively this can also cause over extrusion, when the next time it manages a full Z layer change the built up pressure is released causing over extrusion.

Thanks for the reply, the ptfe tube is brand new as it was replaced with the hot end. I did replace the extruded gear and tensioning arm and that hasn’t made a difference.

How would I check the z layer? I might take the lead screws and motors off, give them a clean and grease and reassemble, maybe something has gone loose or fallen out of alignment

Easiest way is to print a cube say 20mm high and measure with digital callipers.

You can also sometimes visually see a slight slip on a roller you end up going cross eyed after a while watching each wheel bearing going up and down the full height. LOL

I found the solution to this in the end, turned out to be Heat Creep. Like a prat, I had installed the cooling fan duct upside down onto the heat sink, so the throat tube was getting hot higher up the tube that it should do. In my defence, I hadn't noticed that in the installation instructions they turned the assembly upside down in the picture, so I was sure I had the fan the right way up! Well I flipped it over and the prints were better, but still not reliable. Got rid of the rubbish fan that was either supplied or was on the original CR10s, and put a Noctua fan on there instead with the PetsFang mod, also adding the blower, and not had an issue since!

I must say, I learned a lot about the technicalities of how the printer actually works whilst trying to resolve this problem. Oh, and the cheapo PLA has also worked fine since making the swap to the new fan and PetsFang