mini bed leveling, rams into sensors

how exactly does bed leveling work on the mini? couldn’t find explanation in the manual

when i print with nylon, the norm if i do not do anything, is for it to ram into the bed leveling sensors way too far until i have to turn the machine off to avoid it breaking. basically, a little bit of the nylon sticks around at the tip of the nozzle and is not cleared away in the nozzle cleaning step when you hit print, and then this prevents contact between the sensors.

so i am guess the way the sensors work is it needs to detect a metal contact there? and any small blog of material in the way will cause it to fail.

why doesn the z axis just use a touch sensor? it seems really ghetto that it will just plow thru your sensors and just basically break the machine if the sensing does not work.

the only way i am able to print nylons is to wipe the nozzle manually after it goes thru the automatical nozzle wipe process at the back of the bed. since it doesnt really wipe it that good, even with a fresh pad installed.

im not trying to bitch this much since i realize this is only a problem with nylon.

but it seems like it would just be better if the bed leveling sequence occurs while the nozzle is already hot. I noticed the printer at work (robo3d) does it this way. That way, since the plastic is warm, it will just moosh out of the way if there is a little drip at the tip and it will not affect the leveling height. It uses a touch sensor to know when it bumps into the print bed.

Since the mini uses a PEI sheet that would melt with hot nozzle, u dont want to bump into the bed with hot nozzle. but you can just bump into the metal sensors which wont be damaged by the hot nozzle. and just use touch sensors instead of some sort of inductive thing?

seems way more foolproof

Hi daggius

I am not sure if I understan you right:
Do you try to do nozzle cleaning and bed leveling without heating the nozzle?

I have seen best results on my mini with heated nozzle but not to printing temperature.
After some learning curve I realized that I have to adjust the clening temperature per Material just high enough that the retraction works.
This gives the best cleaning results and there for the best bed leveling results.

All the Best
Frank

I just use the defaults. so it cleans and levels at 160 C instead of the print temperature (~240C)

but like i said , with the nylon, it doesnt actually get clean enough for the leveling procedure

I guess you’ll just have to use a scotchbrite pad and clean it yourself before using nylon. shrugs

But yes, it uses a touch system of 5v that acts like a limit switch. And yes, it is really ghetto. Especially because catastrophic failures can happen with an unclean nozzle and they seem to be on the rise.

Ironically Lulzbot originally designed the machine with a backup or failsafe z-axis limit switch (and most likely you have this sensor on your machine now), but it does not actually do anything as they swapped it for the nozzle method and the other switch is not programmed to do anything in the firmware. I consider that to be either poor engineering or a major firmware bug. I have not heard officially if Aleph Objects will fix this issue. I have heard unconfirmed rumors that they will be updating the mini firmware soon to take advantage of some firmware tweaks that were released with the new TAZ 6, but these are just rumors at this point.

I only know this because i built my own mini from scratch and wired it up myself. It bugged the crap out of me when i figured out there is a useless sensor on the machine by design. Still bugs the crap out me.

yeah. but even with a perfectly clean nozzle, it will fail the leveling with nylon since just by heating to 160 and rubbing the pads it somehow dirties the tip. so you have to scrub it in between when it rubs the pads and leveling (either pause or do it on the fly) or else its game over.

i may try to use In-PLA or polycarbonate instead since nylon is a pain

Hi daggius

I have done some nylon (taulman bridge) prints here and had to learn that I had to raise the cleaning temperature to 180°C and make sure that the whiper felt is cleaned from loose nylon rests from the last print.
With that in mind I did not have any problems any further.

All the Best
Frank

I’ve got a Mini and print only with PLA. I’ve done 100’s of prints and only had 1 event where it did not seem to make contact and pushed harder on the pad than it should have. Is it possible that the cleaning pad at the back of the bed is old and full of nylon (that is getting back on the tip during cleaning)? I’ve already replaced my pad once. I also ensure I check the tip often and remove any bits during heating with my fingernails. This has worked well for me so far. …and no burns if you are careful. Although this conductive method of bed leveling has its disadvantages I love it and think its the best thing since sliced break for these printers.