Flow issue for first (bottom) 12 mm of a print
I built my Core One+ from a Mk4S. Everything is working other than a very peculiar issue. I seem to have a flow problem for the first 12mm of the part. On anything I print the walls of first 12mm of the part are noticeably rougher than the rest of the part. I am attributing the roughness to a flow problem, but it may be something else. One note, the wall quality seems to be the worst on the right side/back side of the part. Although the issue can be seen around the entire part.
I have called the Prusa help desk and they first said it was a filament quality issue. I do not think is the problem, because it is a Prusa filament; I dry the filaments and if it was a filament issue, it would be for the entire height. Then they said it was a lubrication issue with the z-axis lead screws. So, I carefully cleaned all of the lead screws and degreased them, but there was no change.
Since then, I have checked on the printer squareness and belt tension and although I did a bit of adjustment, there was no change in the wall quality issue.
I am going to look into the tightness of the mounting fasteners of the z-axis stepper motors, but right now I am grasping at straws.
I did not have this issue when it was a Mk4S. I was hoping to get some help here.
P.S. I can attach a photo, but all that would be seen is a slight difference in the hue of the print color up to 12mm. Let me know if a picture would help.
RE: Flow issue for first (bottom) 12 mm of a print
Not a clue but a photo never hurts. Better would be a 3mf (zipped) file so people can see the settings.
RE: Flow issue for first (bottom) 12 mm of a print
If this happens on different models (with significantly different footprint area), it seems implausible that it would be related to filament flow. The amount of filament used to print the first 12 mm of height will vary wildly across different-sized prints, right?
Some issue with the Z drive would be a logical possibility. I would try the following: Move the heatbed down a few centimeters from its top position, and then -- one at a time -- completely unscrew the M3 screws which hold one of the trapezoidal nuts, so you can rotate the nut up on the lead screw with you fingers and feel whether there is any roughness or excessive friction.
RE:
Well, I started to check the leadscrew nuts, but I came to find all of the fasteners that held the three lead screw nuts were loose. The screws that held the 3 z-axis steppers were also loose. I went through the printer and retightened as many fasteners as I could find. After I tightened up the print the artifact was gone.
I am pretty sure that I had tightened all of the screw during the assembly. I think they loosen during operation. I was not aware of a requirement to retighten the fasteners after use, and I did not use thread locker on the fasteners.
Oh well lesson learned.
RE: Flow issue for first (bottom) 12 mm of a print
First, glad you got rid of the print artefacts!
In my Core One the mounting screws for the motors and trapezoidal nuts have not come loose on their own so far. I had to undo them when I replaced the motors and lead screws a while ago, and they were all nice and tight.
For the trapezoidal nuts, I believe Prusa's most recent guidance in the assembly instructions is to actually keep the M3 screws slightly loose, so the nuts can move laterally? I did not do it that way though. In my understanding, it is sufficient to loosen the screws temporarily during assembly, to let the nuts find lateral positions which agree with where the smooth rods want to position the headbed. Then I tightened the screws again for operation, and have not experienced any Z jams or step losses.