Ender 3v2 nozzle plunging into bed after finishing mesh (only changed springs)

Question

Yesterday I was printing just fine. Today I put the new springs that I bought from Amazon. Swapped them out, went to level things and my Z-offset was of course way off.

I have the Ender3V2-422-BLTUBL-MPC-20230904.bin firmware from mriscoc

I homed and set the probe Z-offset with paper barely grabbing at the tip.

I do the tramming wizard and get it all within limits, do the auto mesh, and it checks out all green (until this last one after several bed digs).

Now when I try to print, it goes through the steps, and when it does the last piece of 25 (back left corner) it just immediately plunges straight down and digs into the bed until I yank the power.

The probe worked fine until that point, and I changed nothing in my settings. The CR Touch triggers every time, until after that 25th square, and then it just dives into the plate and the printer sounds like it's trying to kill itself, and I have to kill the power manually.

Literally, the only thing I did was change the springs. I know I have to figure out how to tighten my arm now and the entire hotend assembly because it's loose after diving into the bed several times.

I hope someone has seen something like this before. I'm at my wits end trying to figure out what is causing this all of a sudden as it doesn't make sense to me. I would maybe understand if it was just digging a little across the board when resetting to start extruding, but the thing just straight-up plunges down and doesn't stop until I kill the power.

Answer 1

It sounds to me like your end-stops positions relative to your new bed level are off or the Z-offset is very off, did you use microsteps and manually checked the Z-offset?

The nozzle crashing into the bed is kind of catastrophic, the bed is maybe much higher than the current end-stops. Could that be the case?

Make sure that the end-stops are high enough to prevent the nozzle from being below bed level and preventing physical damage to the bed. Also make sure that your end-stops are tightly connected to the frame, unable to move to avoid further offsetting issues such as:

As explained in this YouTube video.

Answer 2

I was under the assumption that the 'Z-probe wizard' menu meant when I chose 'auto homing" and it went to the middle, did the probe, finished and went back up, that that position was the Z-home of the printer.

So I then chose the manual offset and leveled it. Tests would run and at the end catastrophic bed plunge.

Then I 'noticed' the 'home Z' or 'move Z home' option (not sure of the exact term as I'm at work) and when I chose it, it immediately dove into the plate.

Solution:

After doing the auto-homing:

• I manually set the Z stop to like +4.00 mm for safety.
• Chose the 'move Z home' and it ended up above the plate this time.
• Choose the manual offset and level as usual, then save the setting.

Tested this time and things worked fine. I had a spot during a print where it got stuck about 75% through, but I think I didn't have the nozzle quite close enough to start.

So the main takeaway is that the 'auto home' wizard doesn't set the initial/starting Z height like I thought it did.