hi, im new here, bought a mini about 3 months ago it has been printing good till the last month, its like a nightmare, ive donde everything to fix the problem but nothing works, when the autolevel process starts, the nozzle pushes the first corner too hard, first the guy that manages the warranty here in ecuador told me that it might be a dirty nozzle, so i cleaned it, removed every dirt and filament, but sometimes it works, but 2 out of 3 it does the same, pushes the first corner too hard, the nozzle its complete clean and shiny, but then i realized thats not the problem because it only pushes the first corner like that, it always perfect inthe other corners, just barely touches, so i have no idea what it could be, and to make it worst, the couple of times i brought the machine to the guy that manages the warranties, the machine works, mostly beacause he only tests it one time, and unfortunately it works when he test it, so he says he doesnt see a problem, and then doesnt believe me, so thats my situation, 2 out of 3 times that happens, so at this point im even wondering if this is damaging the machine even further by forcing the motor and bending the corner when this happens, any ideas? what it could be the problem? how to fix it? (sorry for bad english)
halvertto,
I had the same problem. I did not keep up with cleaning the tip and then about 2 months in, bam! same exact problem as you describe. I let everything cool down and used acetone to clean off the tip. I also cleaned off the metal pads at each corner. I now do this before almost every print. Now this does not happen to me anymore. Also make sure that you are using the newest Cura software.
G
thanks for the reply, i clean it with acetone everytime, and the corners too, and it only happens in the first corner if it was a dirty nozzle it would push the other 3 corners as hard as the first one, and last week i installed the last cura update, so no so sure if its the same problem as yours, i was reading the manual and says that changing the Initial layer thickness and the Intial layer line width in the quality settings might affect the autolevel system (adjust at your own risk) so i was wondering if thats myabe the problem, the default is i think 0.4 for initial layer thickness and 125% for initial layer line width, i changed it to 0.0 and 100%, but never had a problem till last month, i dont see why that would change, what are your settings in quality if i may ask?
All of the Cura settings are important for getting good prints, but they have no effect on the bed leveling procedure.
I’ve been using jrhubott’s firmware for a few weeks now and I have not had one single bed leveling failure in that time. Seriously, not one even when starting up the printer cold with a nozzle covered in black goo. With the stock firmware and PETG, I expected about 1 in 5 to give me trouble even with constant attention and cleaning. The firmware I have on mine is the one linked to in this post: https://forum.lulzbot.com/t/mini-marlin-fw-1-1rc3/2750/1
The install procedure is easy – download the *.hex file.
Open up Cura and from the “Machine” menu, choose “Install Custom Firmware”
Navigate to whereever you downloaded the *.hex file, and upload it. Takes a few seconds.
The firmware prevents the Mini from pressing down too hard on the washers by using the last results to generate a limit. So probably, for the very first probe, you’ll want to make sure everything is really clean.
Ultimately, if you don’t like jrhubott’s firmware, go through the same procedure above but select “install default firmware” to set things back to normal.
If installing the different firmware is not your cup of tea, I would say that I have found PLA to be a real bear – it fails almost every time and needs total babysitting to get through the process. PETG is better than PLA, and ABS is better than PETG. Anyway, if you are using PLA (although the acetone reference makes me think you are not), try a different plastic.
Acetone will only clean ABS residue. If printing PLA, look for a solvent called SCIGRIP 4.
Make sure to check the discs which the nozzle touches during the probing (bed leveling process).
thanks both for replying, and yes i clean the discs too, and no i dont use pla, pla for some reason jams in my lulzbot mini, so i only use abs, since i bought it, ive only use pla like 3 or 4 times.
Yeah, PLA is a nightmare. 
One other thing you could try if you don’t want to change firmware, is to lick your finger and put down a fine layer of spit on each washer just prior to probing. That definitely helps. You’ll want to be just ahead of the nozzle because at 110C for the bed, the washers will dry fast.
The only other non-firmware fix is obsessive compulsive cleaning procedures but honestly, I’d suggest the alternate firmware as being the safer alternative. Months before I tried the firmware, I tried cleaning like mad using bronze wool and the wire brush that comes with machine. Be aware that if you use metal cleaning tools on the nozzle while it is on, you can fry an endstop controller by making a short between the thermistor and the heating block. Then you have to replace the controller board. That quest for a really clean nozzle is how I ended up zapping my board. Now I heat up, turn off, unplug and then clean if I want to get really thorough, except with the alternate firmware I referenced, I’ve mostly stopped cleaning at all.
wait what? haha are you serious about the saliva on the discs? and thanks for the advice
Loosen and relighted the screw on that corner several times.
It might be electrically “dirty”.
Totally. If there is insulating goo unevenly distributed over the nozzle, a thin film of conductive liquid helps the connection form. Before switching firmware, I would use this method to ensure a solid electrical connection.
ill try both suggestions, loosing the screws on that corner and puting saliva aswell, thanks (sorry for bad english)
I’ve made a video of the bed leveling process jrhubott’s firmware does and the first layer, with pics of the final piece at the end. The printer is started from a fully cold state (nozzle reading 7-8 C, bed reading 6 C), the nozzle is covered with carbonized PETG, the bed has visible particles on it and has bubbled substantially, the right front washer even has a speck of plastic on it. Despite all these factors against a successful leveling, it works great (and I didn’t even lick the washers 
).
Aside from taking measurements in a different order, what does the firmware change that improves the success rate of bed probing?
My understanding is that it uses previous results as a limit.
I’ve been using this since some time prior to January 19th and in that time, I’ve not had a single probe failure and the pieces I print look the same as they do with the stock firmware. This is why I’m so gung-ho on this firmware – it really works.
Interesting.
So, if you manually press the corner down from its normal position, with your finger, during probing, will the nozzle continue moving downward until it finds the corner or, does it just stop at the old value it had stored? In other words, how does it handle a deviation from previous results? For example, if you changed the nozzle and it is a little longer / shorter the previous one.
I would expect it to follow the depressed washer up to a certain limit. I wish I could find the thread but I feel like I recall reading that it stops it at 3mm beyond previous results.
Anyway, I’m doing this experiment now and I’ll update this post with a video link when done.
Here are the results. Note, that I haven’t printed anything since yesterday’s video, the printer was again totally cold and not cleaned in any way prior to beginning. I printed 2.5 layers, each layer at 0.25 mm. Caliper result on the 3 layer section is: 0.72mm; on the two layer section: 0.49mm. You can see my bed is totally bubbled so that is going to inject some error. I also have the Z offset lowered by -0.014 in the machine settings. Printing with eSun PETG, measured diameter at 97% flow rate.
video link: https://vid.me/WFIa (seems to follow the washer when manually depressed)
pics:
I’ll have to dig around as well. It sounds like a good safety measure.