Troubleshooting thoughts are solicited and welcome!
Repeating the printing of the same file at the console produces about 1mm of a poorly formed group of layers at different z-positions. Nothing changed from first print to second print. Happens on different files and many of the print jobs result in the defective layer printing behavior.
Fresh Pasta Proto filament used at recommended temperature (205-210) and occurs with both Luban and Simplify3d sliced files. No obvious mechanical issues and have tried alternative filament.
did you check this print for dimensional accuracy on the Z axis? it looks very similar to some prints i have seen when the Z driver overheats and stops moving up. so it prints multiple layers at the same height. you will know that is the case if the height of your print is not what it should be.
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@Atom. Interesting thought! It does look somewhat like the layer has been āsmearedā by the nozzle dragging over it. The overall height measure OK (slightly less height by the same ratio of length measurement to the CAD file dimensions). I would expect the Z axis to be the last to overheat as their motion is a tiny fraction of the X and y axis. However, sometimes the two Z axis linear drives do not move in unison, which I suspect is a firmware issue in the controller. Iāve only noticed the non unison motion on the z -axis. It is easy to notice with Homing and power cycling corrects it for at least one Homing process. Based upon your insight, I think I shall triple check all the cable connections to the two z-axis drives. Thx!
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What a fascinating issue to be having.
If my own experiences say anything, I wonder if you have any loose axis which is sometimes for one reason or another more pronounced than others, butā¦ why would it be the same thickness if that were the case.
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@MooseJuice (interesting handle BTW), Yes, it is almost as if the layer is being repeated causing the significant smearing effect. I can find no loose mechanical aspect and the motion sounds are OK (except when the nozzle is dragging around an apparently existing layer. Iāve submitted this issue to Snapmaker technical support today. The other issue Iāve posted (Z-axis drives not always moving in unison) may actually be another symptom of a common problem??!
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I agree this is a interesting issue. Have you observed the printer while it is printing the layers in question? If not I would try to get it on camera, could be a shake or a wobble maybe. Also what filament are you using? Is it possible that there are bad sections of filament in the roll?
@Atom, the issue is evident with both the Snapmaker provided filament and good quality HTPLA fresh filament from Pasta Proto. I can observe the issue and it appears the comment on āsmearingā over a just printed layer is accurate. I think I can hear and observe the nozzle dragging over existing layer instead of riding just above it. I am printing the same file again (about the 6th time) after re-mating all the cable connections and confirming they are fully seated. I have an enclosure and donāt see any excess movement or stressing of cables. All mechanical aspect seem to be solid and stable, except for the Z-axis motion (occasional non-unison motion of Z-drives when homing observed).
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What about noise? Do you hear a grinding or clicking sounds particularly between layers? Also are these prints measuring the same hight across the print? Could it be that your z hight is getting out of sync at that point in the print and causing the issue?
Simply cut the models in half and take the good top part and glue it to the good bottom part. EZ
I kid, I kidā¦
Hard to tell from the pictures but @jmeckstroth, is this limited to the outer perimeter only? No roughness on the inside?
And I canāt 100% tell, was there a layer shift, or is this sudden overextrusion? Some pictures of all 4 outside walls of the part, along with a picture of the inside wall, would help me out.
Also, would you mind posting the gcode? I donāt suspect itās a problem, but I just like to preview it and orbit around it, helps me think.
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@brent113, thanks for jumping into issue! Snapmaker support is backlogged. What I am now convinced is that the issue is most likely āsmearingā, which appears over the entire layer. On the same part, it can occur on layers with fill (15-20%) or full layers. There is not apparent X or Y shift during or after the number of layers with the āsmearingā. It may be occurring at the time when one of the full layers is injected after so many infill layers (currently set at 20 in the Simplify3D profile), when it occurs?? When the current printing trial is completed, Iāll pull and post the g-code from the USB stick in the A250. Iāve been printing two different parts that exhibit the issue and am currently (after re-mating all cable connectors and confirming all mechanicals are tight) printing both parts together to see if the smearing occurs at the same layer position on both parts (which I expect is the case). I only just started printing with the USB stick (with Simplify3D) after the issues keep occurring with Luban sending files to the A250 via Wi-Fi.
It just occurred to me that if the hotend is somehow shifting, this could explain the symptom?! I will triple check that the hotend captive setscrew is holding the hotend tightly in place. I was unable to wiggle it with my hand (when cold) but it is worth another check!
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Hey what if the nozzle temperature is fluxuating for some reason? Or the sensor which provides the reading?
@MooseJuice. Hmmmm, the temperature display holds very steady, within +0, -1 degree typically. I would expect too cool of a hot end to cause filament extrusion to stop (jamming within the hot end). To me it does not look like a layer adhesion issue. Not sure what symptom being too hot would be?
I perhaps should create a very simple part design, just for testing the issue occurrence and possible fixes over many trials? Maybe a simple hollow cylinder with ~1mm walls that I can print quickly??
@atom and everyone else too - could this be explained by the uneven leadscrew pitch issue? From another thread:
@MooseJuice
could be, but it would be odd for it to do it for so many layers in a row with almost no issues outside of those layers. unless you had it right below an AC vent that turned off for a bit every once in a while. even then though the PID should respond pretty quick. And if it not reading the proper temp the issue would be far more sporadic.
@brent113
I donāt think so, not if homing/power cycling fixes the issue. Also if it was and it was causing these layer problems then it would happen at the same hight all the time. At least everything I have seen about the lead screw issues lend to the idea that they are consistently off at the same number of steps away from home.
The alignment issue sounds like a driver/motor issue to me. Thats why power cycling fixes the issue, it turns off the drivers and then re-homes. Could be skipped steps because of acceleration or jerk settingsā¦ i.e. one rail has a little more resistance then the other, when it jumps to a speed(jerk) or trys to accelerate to quickly one motor canāt provide the torque required and skips a step. From then on the motors are out of sync until you power them down and let the rigidity of the frame square up the system. Then when the motors come back on everything is in sync again.
Edit:
@jmeckstroth next time your out of sync try sending a āM18 Zā over the console, then push the rail manually all the way to the top. Then home and see if they are still out of sync.
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Thanks for the guidance, I shall continue the investigation and attempts to isolate the root cause today.
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I donāt know I am no pro, it was just a thought. Iām sure that the others would know much more than i 
I guess I was just interested in knowing the results so i chimed in
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