Mini 2 inconsistent print start

Heads up, I’m not a pro with 3D printing. I manage exhibits at a kids museum and only have so much time to learn the ropes, though I do have IT troubleshooting and technical background that I’m not a complete beginner.

We installed a new HE 0.5mm tool head for our Mini 2, along with updating with the most recent firmware and selecting the new head on the printer’s info screen. The wiping/probing process before printing is inconsistent. Sometimes it will start its initial heating sequence, then crash into the wiping pad as if the Z height is off; the only thing I’ve been able to resolve that with is restarting the printer and reissuing the print command–sometimes it will take multiple retries of this to clear the issue. I make sure to home the print head via the Lulzbot software before clicking print.

Other times, it’ll wipe as expected, then zoom quickly up to the top, and come back down to probe but crash into the corner, as if Z 0 is far lower than the bed. That, again, is resolved by power cycling the printer and trying the print command again. I just reinstalled the Cura software to see if that helped, but there seems to be no change.

The initial problem (before head replacement) was inconsistent Z offset distance from the left to the right. I can watch the head move up as it goes to the right side of the bed, and also from front to back. I’ve tried the Z offset calibration steps (bring it down to the bed on a piece of paper, move it up until you’re able to move the paper with little resistance), though when I called LulzBot, their tech told me to ignore that and move the offset value as an object is printing. He said that’d give me more immediate feedback instead of guessing like we do with the other technique, though I’ve noticed adjusting the offset during printing isn’t accurate either; if I get it to a sweet spot during a print, then abort and restart the print, the offset is different than what it was when I aborted. However, adjusting the offset still doesn’t resolve the change in the height of the head from the bed as it moves left to right. And I think whatever leveling I do will be for nought with the above problem of crashing, because that groans/clicks as if it’s throwing off any alignment it could have.

The only other potential culprit for the offset creep (that’s apparent to me) is that the toothed pulley wheel wobbles as it rotates, like if a drill bit gets bent while spinning in the drill. It looks like a consistent move, as if it bent but hasn’t bent since.

Thanks in advance for your time and patience with me.

Can you post a (shared/private) video to youtube to show what’s happening?

Inconsistent first layer is almost always contamination on the nozzle. If there’s **any observable movement in the bed when the nozzle touches a corner, your offset will be wrong.

The Mini2 also loses gantry level easily, so putting a mechanical gantry level before trying the wipe and level is (in my opinion) necessary for consistent operation with the Mini2.

Thanks for the feedback! I think it’s best if I can get rid of this weird start before worrying about leveling. What would contamination on the nozzle look like? This is a brand new printhead, only a couple of tests and maybe 4 complete prints under its belt (puns always intended here).

Here’s a capture of the weird calibration sequence.

Here’s one of the crash into the wiping pad.

You posted the same video twice, it’s the crash after a failed bed level.

If a bed level fails, the procedure is part of firmware to run the wipe command (gcode G12).

Glare on the screen prevents me from seeing what the Z axis position is assumed before the wipe attempt, so it’s possible that the Z max is getting tripped early and it assumes it’s near Z180 instead of Z90.

You said latest firmware was installed, but what firmware exactly? Some versions of Cura won’t automatically update from 1.x firmware to the current 2.x firmware, so you have to do that part manually the first time.

If you can post a video from power on to leveling attempt (showing version on the bootscreen), that would be most helpful at this point.

I would definitely recommend downloading the lastest Cura LE and then upgrading the firmware to the lastest version in Cura LE. There was a bug that appeared a while ago where in certain circumstances the printer would get into a state where it would move twice as far as it was commanded to in one direction on the Z axis. It could be up or down, but on yours it would be down, if this is the issue you are having. You can tell if you are seeing this issue by going to the move menu, pick to move 10mm, then turn the dial one click at a time up or down and see that for each click it goes twice as far in one direction than the other.

Note your Z offset, flash the new firmware, reset defaults just to be sure everything is good, then re-enter your Z offset, and see if it works.

Apologies for repeating the video. Prior to the wipe attempt the Z is at 156. I had to not just uninstall Cura and flash new firmware, but clear the cache too. Cody from Lulzbot confirmed this behavior was a common issue with prior firmware. Clearing the cache I think was what was missing from my previous troubleshooting.

It’s now back working, without the weird behavior during calibration, and the current print is 30% without issue. The Z is at 156 prior to wipe, but I don’t get that crash anymore. Thanks for the help all!

EDIT: I ended up taking down the videos due to resolution. If anyone visits this later and wants to confirm if their issue is the same, I can put them back up.