Clicking with gaps and first layer troughs
I have been using a MK2 that was given to me with low prior usage for a month or so and it was going great. But now I am getting the dreaded clicking and extrusion gaps problem. I have read a bunch of threads on it, but figured I would add my own specific symptoms and what I have tried to see if those specifics can be useful to anyone to help me pinpoint the issue or next steps. I can illustrate the effect with this image of first layer and half of second layer before stopping a print:
A few points and then observations. First, I am not certain my z-offset is right, but I did use first layer calibration and got it about the best I thought I could. It happens to currently be at -0.50, but the problems I am seeing occur over a range of offsets. If I get to around -0.40 I start to see gaps indicating too high but much below -0.50 and I get definite squishing. The observation I find curious about the first layer to the left is those odd trough-like variations that run 90 degrees perpendicular to the direction the first layer was printed. There is somewhat of a regularity to them but I will say the underside of the print is perfectly smooth with no gaps. I suspect the troughs are one of the symptoms of extrusion issues associated with the same problem I get starting with the second layer. Note that during first layer I do not detect any clicking.
When the second layer goes down, you then see on the right the gaps in the filament. Each gaps is associated with a click. When ovserving the hobbed pulley that feeds the filament, each click is observed to correspond to the pulley seeming to jump rotationally backwards just a bit, effectively retracting the filament and I assume thereby not extruding at that spot.
Things I have tried (not necessarily in order):
- I tried different spools of filament to make sure it was not a bad spool.
- I also dried the filament in a filament dryer as well still concerned about the filament.
- I changed to a brand new nozzle (FYI in all cases I am using an 0.4mm brass nozzle.)
- I tried loosening and tightening the idler screws from everywhere from too loose to fairly tight. They are currently just a bit tighter than the 13mm normal position, probably around 12.5mm.
- I did multiple cold pulls, and am getting a nicely shaped end coming out on the cold pull.
One other sympton besides the gaps is I do find that after a cold pull, when I reheat and then load the filament again, sometimes if seems to stop going through and takes a couple rounds of telling it to load to finally get filament flowing through. I also after reloading the filament have tried running the gcode file to just extrude 100mm of filament. Note that I had done that both before and after a number of these steps and it actually consistently extrudes 96mm of filament instead of 100 regardless of loosening or tightening the idler screws. I have adjusted my extrusion multiplier to 1.04 in PrusaSlicer to compensate for the fact that 100mm comes out as 96mm.
Every time I have tried any/each of the above, I have tried printing again and get the same result with clicking. Also, it does seem to matter the speed I am printiung at. These tests are all using the 0.35 mm FAST print setting. Printing at 0.20 NORMAL reduces, but does not fully eliminate, the problem. I could slow the printer down more, but for larger prints that do not require detail, that of course adds a lot of time to printing. Also, the 0.35mm FAST speed worked fine for weeks for bulkier prints. It is just in the last several days that now I have the clicking problem.
Things I have not tried:
- Taking apart the extruder assembly.
I am guessing that is my next step is to start to take things apart. My gut says perhaos I have an issue with the PTFE tube or the hotend heat sink. But before I start pulling it all apart (which can;t happen for a couple weeks anyway) I am open to other tests I could run to further diagnose what is going on.
Thanks,
-Ed Hinton
RE: Clicking with gaps and first layer troughs
One more thing. Just to make sure I had not messed up my settings in PrusaSlicer in a way that would cause it, I went ahead and reran configuration in PrusaSlicer and checked the box to delete profiles so it would be back to original setting. I then pulled the STL file again for my test print (2x2 square), generated the gcode for it at the built in 0.35mm FAST setting without modifying anything, and tried printing it. Same clicking problem.
RE: Clicking with gaps and first layer troughs
SOLVED. I did not have to do any disassembly after all. The problem was the layer height and print speed. 0.35mm FAST was too much for my 0.4mm nozzle. I had seen some of the issue at 0.2mm layer height, but that was AFTER the problem had developed at 0.35mm and BEFORE I had done the multiple cold pulls. It appears that the too fast extrusion for that nozzle size had caused some amount of blockage above the nozzle and the multiple cold pulls must have cleared it. But since I had then gone right back to trying to see if the 0.35mm FAST printing was working well, it just recreated the problem. I do not know why when I first started using the printer I had gotten away with 0.35mm FAST prints, but perhaps until the problem first developed it was less prone. There very well could have been some movement it caused of the PTFS tube which is why I may still replace it at some point and add a collett clip. But for now I will leave it be.
As for the troughs on the first lyer, I was wrong about the Z offset being good. I was pointed to this print for doing a better live calibration of the z-offset.
https://www.thingiverse.com/thing:4894942
Using the 5x5 grid and varying the z-offset by .05 at a time while it printed and then narrowing in and doing it again adjusting by .025mm at a time, I settled on 0.43 as my z-offset. No trough and now that the clicking probem is gone by printing at 0.25mm layer height rather than 0.35 FAST, all is well. I did order some replacement PTFE tube in case I do decide at some point to change it out and add a collett. But I will probably just keep that in reserve if I see future issues.
-Ed Hinton