MK3S Extruder is Not Printing Reliably  

MK3S Extruder is Not Printing Reliably

I have a MK3S and a MK2.5.  The MK3S has been a reliable machine until recently and the Mk2.5 has been a workhorse.  Over the past 3 weeks, the reliably of the MK3.5S has suffered tremendously.  The print begins to fail about at layer 2-4 on a snowflake ornament that I printed for my grandson about 3 weeks ago.  When we did our session together, we had 2 failures out of 4 prints that we attempted. Now at 3 weeks, it is every print.  I thought it might be poor PLA so I tried it on my MK2.5 today using the same settings on Simplify3D and got a perfect print on the first attempt.

The nature of the failure is 2 fold: 1) the printer is oozing blobs of filament which results in missing pieces of the first layer and provides an area where the nozzle catches and jams up the print and 2) the print does not appear to have good bed adhesion so the print also starts to lift contributing to the failure.  I am using PLA.  I worked on failure number 1 by adjusting the retraction, coasting, and speed which seemed to help a little, but still results in blobs and missed sections that can caught up by the nozzle.  I have worked #2 by adjusting bed temperature from 60 to 70 deg C to aid adhesion of the first layers going to 65 then 60 by layer 4.  I also have adjusted the nozzle temperature for 215 at the first layer and 210 by the 2nd layer.  I also adjusted the cooling fan timing.  All this has helped very little.  Again, using these same settings on my MK2.5 gave a perfect result so it is not the PLA filament.

I also notice that the extruder cover that holds the extruder in place had a weak, thin area that the heat had deformed.  I thought this might be a catch point.  So I printed a rev 5 version of the the part that has a sturdier section in that area that should not deform.  This did not reduce the catching.  I did find some of the extruder bolts that hold the extruder together were loose and tighten them up with no change in performance.  Another thing I have noticed is that the SD card reader is loose and sometimes requires an extra push to get it to register.  The MK2.5S is very tight.  I ordered a new LCD screen to resolve this issue.  I have run the first layer calibration to get the best Z adjustment.  I am getting good results with the calibration, but it does not seem to impact the problem.

Net, I do not know the what I should do from here.  All the basic test checks come out positive and does not identify any equipment issue. I am beginning to wonder if I have a problem with the extruder and need to replace it.  Or change out the nozzle which I have one that I could replace it with.  Or should I do a complete rebuilt of the extruder system itself?  This machine has become completely unreliable and nothing seems obvious to solve it.  Any ideas to try or recommendations would be appreciated.

Mark4E