Z-level height

Mini 2 - I am getting very frustrated - maybe because I am still new to this and still learning.

I print and everything works fine. Then with a new print all of a sudden the nozzle seem to be plowing through the first and following layers, messing up the whole print. This is after nothing on the printer was changed - not even the filament.
I have googled this problem and it seems to be a z-leveling problem, which I have tried to adjust but does not seem to make a difference.
If I could only figure out why this only happens some times? I sometimes print exactly the same print from my SD card twice and in the one instance the print would be perfect and in the next it is a big mess.

Please help!!

Sorry to hear about the difficulty! Your printers automatic bed leveling procedure is done by electrical contact. The most common way this will fail is due to a dirty nozzle that prevents this contact until the filament is “pushed” to the sides and electrical contact is made. This will cause your printer to think the bed is lower than it actually is, and run the nozzle into the bed when the print starts. If you see a deflection during the probing sequence, turn off the printer and restart the print.

I would suggest checking that your wiper pad isn’t looking worn out. If you do need to swap out your wiper pad you should have some spares within your toolkit, and you can even flip them over to use them twice! This will help ensure a nice clean nozzle before each print. You will also need to clean off the printhead by hand to ensure a clean nozzle. Raise the printhead off the bed, and bring to extrusion temperature. Using a thick leather glove and a clean blue shop towel gently wipe off the outside of the nozzle. Using a non-conductive Scotch Brite pad to clean the nozzle is also very effective. The one thing that you will want to avoid when cleaning is anything metal, the printers hotend is susceptible to electric static discharge that can damage the hotend, so avoid using any kind of wire brush. This is a good time for a visual inspection of the corner washers to assure no filament has accumulated on them as well.

Also, what filament are you working with (type, brand, and diameter)? It is possible that you might need to adjust your wiping or probing temperature to ensure the nozzle is clean when it is coming down to make contact with your build plate.

The same thing happened to me and I eventually found that the nozzle had come loose and unscrewed which lowered it onto the bed.

Thanks, I have in fact picked up that my wiper pad was quite worn and flipped it over.

I use only PLA and this has happened with different suppliers’ filaments.

Will keep an eye on that nozzle to make sure it is clean for now. :slight_smile:

I am being very meticulous to clean the nozzle before every print but it is starting to happen again. :frowning:

What I have come to realise is that whenever I put more than one item on the bed to print this starts happening.

If I only print a single item on the bed it seems to be better.

Is there a possibility that the firmware is having a glitch when printing multiple items at a time?

Please help!!! :question:

No. The cleaning / auto-leveling commands are part of the start gcode. This gcode only has knowledge of a few settings (i.e. temperatures) and knows nothing about what objects have been placed for slicing. The firmware processes the .gcode linearly one command at a time so it also knows nothing about what is coming next.

You can verify this for yourself by examining the .gcode with a text editor for jobs with one item vs. jobs with multiple items.

My Mini (type1) used to gauge the Z-axis height during the pre-printing stage (just after nozzle cleaning) by descending to each of the metal discs at the corners of the buildplate in turn. The nozzle would touch a disc, back off about 1 cm, then come down more slowly and just “kiss” the disc, and retract – then onto the next corner etc. Now, on the “second” approach instead of “kissing” the disc it remains touching it for about 1 second and meanwhile you can hear the z-axis motor still trying to turn. (It gives 3 or 4 little “tock-tock-tock” sounds). Then the nozzle backs off and does exactly the same with the other corner discs.
Has the latest software update changed the way that leveling is done, or do I need to clean the nozzle tip to ensure better electrical contact with the discs? The Z-axis offset and Estep value are correct for my machine (I always check them when up-dating the firmware). I am using Cura:3.6.20, Firmware: I am using ABS. The nozzle wiper is new.
Strangley enough, the parts turn out as good as ever in spite of this leveling business.

Update: I cleaned the nozzle with acetone so it would make good contact with the four corner discs. I checked that there was good contact with a multimeter set to ohms. However, this did NOT cure the problem. I’m guessing there is a poor connection either from the corner discs or from the printing head to the circuit board. A broken wire? A corroded multipoint plug? I need to investigate.