Auto Leveling

I have had my mini for 10 days now and over the last few days the auto leveling has become more and more difficult. I have ensured that the nozzle is completely clean by cleaning it while it is hot with a cloth and I have changed the wipe pad. Even if the nozzle is completely clean (inspected with a flashlight after it comes off the auto wipe pad) it still wants to depress the first of the four stops a slight amount during the fast descent. The slow descent is OK and the other four stops are OK but the first stop is an issue. What could be causing this other than a dirty nozzle and how would I fix it?

I think it’s OK if the fast descent pushes the bed a little bit. It’s like when the X/Y home is done. Go fast to the endstop, back up, go slow so you end up right on.

I might be corrected as I’m new as well, about a month. However, my prints including the first layer have been working well. It also matches what I’ve seen in various youtube videos demonstrating the process.

You might see a slight depression of the corner washer on the fast move. You should see no movement on the slow tap.

Hmm, well I have had some prints with absolutely no bed deflection and they come out very well. I have also had some prints with a lot of bed deflection and they are a disaster. The prints with only a little bed deflection come out pretty good but the surface detail isn’t quite as good as the ones with no deflection which is why I think even some deflection isn’t good. I suppose this could be my imagination but I don’t think so. I’ll see if I can post some example pictures later when I get home.

Have you tried cleaning the top of the washer? It might have a thin layer of something on it that only melts on the slower touch routine, and the fast tap does not melt it. YMMV

I have tried cleaning the washers, they seem clean.

I switched the wipe to a scotch pad as someone suggested in another thread, tried the leveling three times, perfect once and almost perfect twice, much better. The stock wipe pad is pretty bad for leaving little fibres on the nozzle, maybe it’s leaving some small ones that I can’t see that are interfering with the probe to washer connection.

Add an end-script to perform the nozzle wipe process. Since the nozzle is still hot, seems like the perfect time to clean filament…

I’ve moved to performing both the leveling and cleaning to be manually initiated processes.

I just do them prior to printing until I’m happy with the leveling results and then I start printing. Sometimes I print several objects before running the leveling again. I have also modified the firmware to not reset the leveling matrix on initialization of the axis’s(G28).

I also always perform the leveling with the bed and nozzle at the print temperatures for the filament.

I have been thinking about storing the calibration matrix in EEPROM but at this point and time I’m okay with performing the leveling sequence whenever I turn on the device. May do some testing to see how much variance I get if I was to store the calibration.

Jason

Try flipping or replacing the wiper pad. If the wiper pad has too much plastic wiped off on it, the hot nozzle will get plastic smeared back onto it rather than wiped off, undoing your scotchbrite cleaning.

I have gotten into the habit of watching my mini while it auto levels.
Watch the Cura status window and it will tell you a lot about how well it aligns.
When it slowly approaches the washers at the four corners, it reports the distance of the limits for Z.
After you watch it a few times, you will get an idea what numbers are typical, and what are way off. Write them down if it helps.
If you see it miss the numbers by more than a couple tenths of a mm, it will probably yield a bad print. Abort!

Here’s how I abort:
Turn off the power switch on the mini for only a couple seconds, then turn it back on.
Wait for the Cura control panel to show “Print” in darker letters, indicating it is initialized.
Quickly hit the Z home button (blue icon).
While it is retracting, wipe the nozzle with a paper towel as it should still be warm. Clean it as best you can.

At this time, it will have retracted about 30 to 40 mm of filament as part of the leveling step, and if you start it up again, it will retract even more, causing it to skip printing for a while, which is undesirable of course. So heat up the nozzle to normal extrusion temp by typing in the number and pressing the appropriate “Set” button to the right of the number window. Once it reaches the correct temperature, extrude about 40mm of filament (10mm at a time) until it flows cleanly. Then turn off the print head heater (0 and Set) and clean the nozzle with your paper towel as it cools. It may ooze just a bit, and maybe retracting 10mm might help this. I just keep wiping until it’s clean.

Then restart your print, and it will go through the homing, warming, wiping, and leveling process again. If the numbers look right in the status window, you should have a good print this time.

Here’s a screen shot showing a bad leveling run which I aborted:
Note the numbers are off by more than 0.5mm.


Here’s a screen shot showing a good leveling run which printed very well:
Note the numbers are within a couple tenths of a mm.

I was able to get very repeatable numbers with a warmed up system and a good clean nozzle.
I also have my four corner values written down so I know when it’s “close enough”. These numbers do change slightly, but if they change significantly, I know something went wrong and dump the print before it starts.

Good luck all, and let me know how this works on your mini if you try it.

I have tried flipping/replacing the wipe pad and that helps for a few prints but it quickly degrades to the point where it is leaving fine hairs that are disturbing the contact and auto leveling sequence. Having said that this problem is behind me, I have had nothing but perfect auto levels since I replaced the stock wipe pad with a Teflon safe scotch brite pad. I also ensure that I give the nozzle a quick wipe while it is still hot (right after the print) to get any residual plastic off. If I am not there when the print ends and the nozzle has a fair amount of plastic on it I will heat it up and wipe it down before I start the print. The scotch brite pad does a good job cleaning the nozzle and leaves no hairs on it, it is also quick to flip/change and is much cheaper than the stock wipes.

I’d just like to add that if you abort the print during auto-leveling, just manually push the filament down with you hands as far as you can to undo that initial retraction amount. No need to waste all that extra time heating, extruding, and cleaning! I’ve done this many times with no problems with a default skirt length.

Good tip with the scotch-brite pad, I’m going to give that a go!

I have had the same issue in the past with the nozzle pressing down too hard on the four metal discs, even when ensuring the nozzle was perfectly clean. What fixes it for me is to make sure that the discs are absolutely polished with no dull finish. I keep a Mr. Clean Magic Eraser nearby and hit each one in a light circular motion to shine them up. YMMV

I recently had reason to run some PLA through my machine (my experience is that PLA is a nightmare for the autoleveling). I finally just licked my finger, and when the head was descending to the wiper pad, spread a fine layer of spit on each washer. It helped an awful lot without changing the results from normal. I think PLA leaves some very thin non-conductive residue and a little layer of spit helps the electricity find the holes in that layer. I also used some very fine wet/dry to polish the washers beforehand.

So, spit and polish (or more accurately, polish and spit) …

What temp are you wiping and probing at?

I use the standard lulzbot Cura settings for wiping and probing for ABS and PLA. For PETG, I use 160 for wiping and probing, but it’s really only with PLA that have issues with the bed leveling.

I’ve updated the Marlin firmware to auto pause if the auto-leveling is off by more then .3mm from the last time it auto-leveled at each position.

When it pauses it also moves the head to the front and up to allow for examination and cleaning. If you choose to resume it will attempt the auto-leveling again from the beginning.

This works good for me and I only really see issues when using PLA and require additional cleaning.

Jason

You might try wiping and probing at a slightly lower temp. That has helped me with some of the pla I print. Also, make sure the nozzle doesn’t start warming directly after the wipe. I have had the best luck wiping and probing at the same temp.

That’s an awesome idea – I’m going to give your version a try