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Extruder Head Lowering During Print

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Please see the attached photo. I have no idea how this happens. I have checked the G-code from the logs and it does not show anything untoward. I have also lubricated both Z-axes on the printer (it has been upgraded to have two). This has happened twice now at the same height, Luckily I was sitting in the lab when this happened and I could hear the print snap. Any ideas on how to prevent this would be appreciated.

Ciph3rdoc;

Did you get your Z axis problem sorted out?
I was wondering if you had the problem on all your prints or just the one in your photo?
I have had the print head get stuck in the middle of a large fill area due to excess plastic building up on the tip and wind up making a hole similar to what you have. The fix in that case was to replace the nozzle as it was wearing out and opening up. If you are having the issue on all prints check to see if the X,Y, or Z axis cables are hanging up somewhere. Let us know what your fix is.

Hey! Sorry to all that commented in that I did not respond. It has been busy and I just now got around to answering. Anyway, I did find the issue. I had just installed the dual z axis upgrade to the printer. This upgrade came with two mounting blocks for the top of the lead screws. Those blocks are what was causing the issue. With them installed, it is near impossible to get the heights equal as the head travels up. So, what happens is one of the lead screws will "jump" down when the difference becomes too much. That is what was happening. I noticed it did it twice at the same height (about 75mm). I took the blocks off and now it prints perfectly. So, in a nutshell, the mounting blocks are not needed. Allow the top of the lead screw to float at the top.

That looks like a pretty severe "drop" of several mm, but it can be hard to say if those deep holes were just caused by chaos after the part detached from the bed. Have you been able to observe it the z is driven down, or if it seems to just lose power? What are you using for z-drivers, current settings,... stock motors?

I would tend to lean towards an intermittent connection, but that's a bit rare on a8 z motors (since those wires don't usually move much if at all).

Please see the reply to hggomes above. It was one of the lead screws jumping.

What do you slice with?
I was getting layer shifts with Cura 4.12 so dropped back to an earlier version and the shifts went away.
Just my .02¢

I have been using Cura 4.11. I agree with the non-use of 4.12. Until they take care of the kinks, I am not changing. I also dabble with IdeaMaker but it gets confusing sometimes with all the adjustments.

Thanks. I knew it wasn't me... :-)

That would be weird if a slicer caused layer shift. I'd keep fingers crossed that it doesn't come back at some point with the new slicer.

Had a plate of 9 parts bins to print.
Sliced in 4.12, on both my machines, they layer shifted.
Used the same profiles, materials, speed, etc, sliced in 4.6, they both ran to completion fine.
It's happened to me with other parts as well on 4.12
They're both RAMPS1.6+ with 2208's on Marlin1.1.9, literally identical machines, so go figure.
It is what it is.