Nozzle crash during auto-leveling procedure

Just got my Mini two days ago and have been loving it. However I started noticing some odd behavior last night, and it has been continuing today.

Intermittently (I think I might be starting to figure out what may be triggering it, but I’ll save that for later), the nozzle will crash hard onto the first washer during the auto-leveling process. When this occurs the head will move over to the washer after the wiping process and start the fast descent. Normally it will transition into a slow descent before making contact, but in this case it will just keep on going and crash into the washer with enough force to deflect the bed down by approximately 1/8". The head will then come back up, and the rest of the auto-leveling process seems to complete nominally. On one occasion I observed the nozzle crashing onto the second and third washer as well. Once this behavior starts it is persistent until the printer is power cycled and Cura restarted.

The nozzle is generally visually clean of any material when this occurs. Even if the nozzle had contaminates on it I don’t think electrical contact problems are the issue. This conclusion is based on the fact that the head doesn’t transition from the fast descent into the slow descent.

It seems like this behavior occurs after a failed print (angel hair followed by a ‘Cancel’ in the control dialog), and if the Mini has been sitting idle for 3-4 hours.

Any ideas / suggestions? The amount of force that the head must be exerting onto the bed is a bit troubling…


Read through this thread and see if anything there helps.

I found that thread, but I have to admit it was late and I didn’t read all the way though. The problem discussed there does sound very similar to the one I’m encountering and I’ll incorporate the suggestions.

However, the fact that in the situation I’m describing the head never transitions from fast descent into slow descent seems to indicate that something has gone wrong even before it is trying to sense electrical contact. My feeling is that the z-axis datum reference has been lost somehow, but that is a guess.

Everything in the start g-code makes sense, but I am interested in finding out what is inside the G29 subroutine. It seems that this is a routine embedded within the firmware?

In any case, I’ll be extra particular about cleaning the nozzle and see if the problem persists…

It is normal for the nozzle to tap the washer at the higher speed then move up and tap again at a slower speed. If the nozzle is dirty enough to interfere with the electrical connection, you will see a bed deflection during both tap operations.

Bring your nozzle to printing temps and give it a vigorous rubbing with a folded washcloth. Be careful so you don’t burn yourself.

Another thing to watch is that after the wipe command prior to auto level, the felt pad can leave some fibers on the tip of the nozzle. If those fibers are in the way, the connection of metal nozzle to metal disk on the bed will be difficult and won’t make a good connection. Even a few fibers of felt will do it.

My suggestion is to take your tweezers, and as the extruder is approaching the first tab on auto level, pick any fuzzy stuff off the tip.

You will find the more you use the felt pad, the more fuzzy you will get.

Gee whiz forget the tweezers and wash cloth. You can purchase those same Scotchbrite like pads at the supermarket, get some, cut in usable sizes and wipe off the hot nozzle. When I remove the roll from the machine I snip filament off just above the feed about a 1/2 inch (6mm) or so, When reloading I heat the head up in CURA machine control, when its hot enough I pull out that old stub and feed in the filament, and lock down the catch. I then extrude some filament to make sure its working ok, and clean off the nozzle with that Scotch brite pad.

Hit Print, the head cools down and does the auto leveling thing and all is good. Make sure those screws holding the washers down are tight, one of mine was loose.

I too experienced nozzle crashes recently during the auto-level procedure.

Given the advice I found on this board I cleaned the nozzle. While I got the printer working again, it was not very reliable anymore. Sometimes it took “3 crashes” before getting a successful pass of the procedure.

After much mucking around I finally found the root cause: the screw that secures the ground wire to the hot-end was loose – despite having a shake-proof washer on it. I tightened it down and now the printer is as reliable as it was before.
I guess the heat cycles caused the screw to loosen.

I was going to suggest a loose screw on one of the belt drive pulleys. Glad you found it, and you might check the rest of those screws, vibration running can loosen. I love my Mini and I have a nearly new TAZ 5 coming for the larger things.