Lulzbot Mini requires huge maintenance

A forum dedicated to the stock LulzBot Mini 3D Printer
IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Tue Nov 13, 2018 4:32 pm

Thanks for the response.

I agree oozing or dribbling is often caused by the printhead temperature being too high. Setting aside the fact that this is the same filament we've always used, I've been slowly lowering the temperature trying to address it. I'm now down to 200C when the label on the spool recommends 235C, and it's still dribbling away.

I posted an earlier thread about the print nozzle temperature being wildly inaccurate. I have a calibrated Fluke temperature probe and the nozzle temperature runs anywhere from 10-30C cooler than what Cura reports. Not much of a confidence builder.

I said earlier I was done with this piece of junk, but being a tech-head I just can't stop fiddling with a problem. {grin} I just ran through another startup cycle, carefully observing everything, and now I notice that when it does it bed leveling operation the nozzle tip misses the front right washer! It finally touches on the shoulder of the nozzle rather than the tip, which undoubtedly adds negative Z to the measurement. The nozzle used to touch evenly on all washers, I've watched it carefully in the past since excessive pressure during auto-leveling indicates contamination of the nozzle tip. WHY would this change? I first thought "OK, I must have mispositioned the washers when installing that expensive bed plus expensive heater they made me purchase" but the washer screws go into tapped holes in the plate - it's impossible to misposition them.

Since the washers cannot have moved, this is yet ANOTHER mechanical misalignment problem with this thing. Maybe the limit switches moved? Maybe some other 3D piece has cracked and allowed things to shift out of alignment? It touches three of the four washers properly, yet misses the fourth. They're in a square, so the X-Y distances are the same all the way around, yet it can't even do this?

My opinion drops further every time I work with it.

Meanwhile, on the nozzle and filament, I've determined that no matter what settings I use, the biggest problem is that filament curls up and touches the side of the nozzle. This occurs even if I manage to get the Z axis offset to the point where it starts to lay down a successful first layer. At some point, the filament extrudes in such a way that it touches the tip of the nozzle - and once that happens it starts dragging this thread around, which turns into a blob on the nozzle, which destroys the print. Doesn't even get through the first layer before this happens. I've tried pulling the blob away from the nozzle, accepting the print is bad but hoping get more diagnostic data, but it lays down a couple centimeters properly and then the filament grabs the side of the nozzle and it's lather, rinse, repeat.

ARRRRGGGGHHHH!!! $1200, plus new bed, plus new heater, plus new fans, for THIS?!?
Last edited by IDEngineer on Wed Nov 14, 2018 8:19 pm, edited 1 time in total.

IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Tue Nov 13, 2018 7:37 pm

Additional things I've tried today:

* Removed the nozzle for inspection and cleaning. Hole looks fine. Could see daylight through the nozzle. Used 0.3, 0.4, and finally 0.5mm drill bits to gently clean it out and insure that the hole in the tip was round and not misshapen. No improvement.

* Decreased the bed temp from default of 60C to 30C to improve PLA adhesion. No improvement.

* Increased the bed temp to 70C to improve PLA adhesion. No improvement.

Bottom line: The filament continues to flow fine when tested away from the bed, but immediately forms a huge blob and rips the first layer away when at the bed surface. Next I'm going to play - AGAIN - with Z axis offset settings. I'm going to back it off so far that it just drools out a round string of filament, then slowly step the setting closer to the bed in the hopes that I get some sort of adhesion. If that fails, I may reinstall the old original print bed in case this @#$%@%$^'ing expensive new Lulzbot print bed AND its !#$%!%'ing expensive separate heater turn out to be a DOWNGRADE.

IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Tue Nov 13, 2018 7:54 pm

Latest update: I backed off the Z axis offset and finally got the nozzle to extrude near the print bed. As expected, it basically trailed a thread which dropped down onto the bed behind the nozzle. It got no "squish", of course, so it didn't adhere very well and as soon as the nozzle came back around it snagged it and tore it off the bed. Not unexpected.

So the obvious next step was to increase the negative value of the Z axis offset ever so slightly, so bring the nozzle just a bit closer to the print bed and thus gain some "squish" to help the first layer adhere to the bed. I went up by 0.05, and... we're back to just a big blob of filament on the nozzle. Nothing on the print bed at all. Just an ever-enlarging blob on the end of the nozzle.

My gut tells me this may be a flawed nozzle, despite my careful inspection and cleaning of it. I don't have a spare to compare against. Anyone have experience with aged nozzles? Do these symptoms sound like that could be a/the cause?

Despite being completely disgusted with this Lulzbot Mini, I'm trying really hard to help it work. I've put about 6 hours into it, just today, ignoring my other work responsibilities. But it just seems to be too deteriorated, there are too many things wrong. Won't adhere, constantly forms blobs on the nozzle, X-Y positioning can't find one of the four leveling washers... and all of those are independent problems. What single common thing would cause all of those failures? Some of these problems have been around since about a month after it arrived new from Lulzbot, but now the new problems just keep piling on. It's hard to consider this thing a good investment, especially at the price.

IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Wed Nov 14, 2018 2:49 pm

At the suggestion of a very helpful forum member, I checked the X and Y steppers on this cursed Mini. Apparently others have experienced this failure to align with the leveling washers, and it was due to cracked motor shafts in the lower-quality steppers on the X and/or Y axes.

Turns out my Mini has the better, connectorized "Moons" steppers on the X and Y axes. I relieved the belt tension and removed the motors, and the shafts appear perfect. They are not broken and cannot be pulled out of the motor housing like the failures described for the lesser steppers.

Sadly, my Mini does appear to have the lower quality steppers in the two Z axis positions and the filament drive mechanism. However, at least for the failure to X/Y align on the leveling washer, those three steppers cannot be the issue.

Thus we still have the unresolved question of "Why does this Mini now fail to find the front-left leveling washer, when it previously used to?" :evil: :evil: :evil:

mwester
Posts: 54
Joined: Sun Nov 26, 2017 8:02 pm

Re: Lulzbot Mini requires huge maintenance

Post by mwester » Wed Nov 14, 2018 3:23 pm

I picked up a slightly abused mini (store return) for a song, and rebuilt it. It had the same problem you describe -- missing the washer when probing. To make a long story short, my first fix worked great, but was wrong (I printed a few 1mm thick shims to put between the head and the mount, so that the head would sit further forward and touch the washer correctly. I later learned that the Y-axis stepper is quite capable of shifting the actual Y-axis rod positions in their holes, in this case when the original owner had crashed the head into the bed with sufficient force to embed it into the PEI layer and prevent the bed from moving freely.

In a nutshell, the Y-axis rods are not intended to "bottom out" in their pockets at both ends. They are normally secured with set-screws. When the Y-axis is in motion, the force acting on the bearings on the end opposite the motor is pulling that bearing assembly toward the motor -- if the set-screws are unable to hold the rods in place, then one or both of the ends of the printed plastic brackets will be pulled toward each other until the rods bottom-out. This has the side-effect of loosening the Y-axis belt, but worse, it can shift the Y-axis end-stop. In my case, the shift was enough to cause the "home" position to shift in the Y direction so that the probe missed the washer.

Either solution will work -- you can re-adjust the Y-axis rods, or use shims. I ran that mini with the shims for the longest time, very happily. (I confess that I just don't trust the set-screws -- and in retrospect, I should have put a few spacers (such as thin washers) into the pockets of the Y-axis rods, so that they bottomed out in the correct position.)

IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Wed Nov 14, 2018 3:46 pm

mwester wrote:
Wed Nov 14, 2018 3:23 pm
the Y-axis rods are not intended to "bottom out" in their pockets at both ends. They are normally secured with set-screws. When the Y-axis is in motion, the force acting on the bearings on the end opposite the motor is pulling that bearing assembly toward the motor -- if the set-screws are unable to hold the rods in place, then one or both of the ends of the printed plastic brackets will be pulled toward each other until the rods bottom-out. This has the side-effect of loosening the Y-axis belt, but worse, it can shift the Y-axis end-stop. In my case, the shift was enough to cause the "home" position to shift in the Y direction so that the probe missed the washer.
Thanks for the reply!

Based on your comments, I just checked the entire Y axis mechanism. Both rods are firm in their mounts, no movement in any axis. The mounts themselves are also solid to the frame. Nothing in the Y axis system has any play at all, except the belt which has normal tension for a toothed belt.

Then I ran the Y axis while checking the belt, to see if the belt tension changed during movement. Nope - the belt tension seems consistent, as it should.

I should mention here that the misalignment on the front-left (second) washer is in BOTH axes. The nozzle is offset toward the center of the printbed, meaning it has an error in both the X and Y axes. It's not just a shift in one direction. Also, the alignment is correct on the other three washers... it's not "on the other three but shifted too far one way or the other". It's just the second washer, the front-left one, where the nozzle misses and it appears (roughly) to be missing the same amount on both axes because the mispositioning is roughly equal on both, causing the nozzle to be diagonally closer to the center of the printbed.

Grrrrr.....

IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Wed Nov 14, 2018 5:02 pm

Well... we finally have a partial answer. At least to the washer misalignment question. It turns out the X axis limit switch relies on a 3D printed part from Lulzbot. And that 3D printed part is either badly designed, or was misprinted for my Mini.

Here is a photo of the right-side X axis limit switch as it approaches the surface that is supposed to actuate it:
Image

See how the switch body will contact the 3D printed part? That's great, but the switch actuator is coplanar to the switch body, so whatever is supposed to actuate the switch has to be no higher than the part that touches the switch body. Ahem... see that curve on the 3D part? Now see what happens when the switch actually contacts the 3D part:
Image

Now the switch body is touching the 3D part. But the switch actuator isn't depressed. The curve on the 3D part isn't coplanar with the upper portion that touches the switch body first, so the carriage runs into the physical stop before the switch can be triggered. I'm not sure how the Mini's firmware handles a hard physical stop before the limit switch actuates, but this all happens RIGHT AT THE POINT where the nozzle should be coming over the second leveling washer. Coincidence? I think not.

I have a Catch-22 in that I cannot run the 3D printer, so I can't just casually crank out a replacement part. For that matter, it's very clear from close examination that the part was designed with this curve/slope/bevel from the start... I have other end-on photos that show the upper layers terracing back to form an angle. It's intentional, even though I cannot imagine how it was intended to work or ever did work properly. At first I thought "Ah ha, this is an easy fix, just loosen the switch mounting screws and move the switch into a better position" since most of the time mounting holes for switches like this are elongated to allow alignment. Not here! Loosening the screws afforded ZERO movement. So instead of moving the switch, I'm going to manually build up the plastic on that curved section so it becomes coplanar with the rest of that part, like it should have been all along.

Back in a little while after mods (really, correction of design errors) is complete.

IDEngineer
Posts: 33
Joined: Sun Feb 05, 2017 2:36 pm

Re: Lulzbot Mini requires huge maintenance

Post by IDEngineer » Wed Nov 14, 2018 8:16 pm

Lacking a second 3D printer to generate a "formal" part, and not knowing if the Lulzbot print file is still misdesigned to generate the bad part on my Mini, I resorted to the original 3D printing material - JBWeld! (Specifically, JBKwik so it didn't take 24 hours to cure.)

I first created a rough support structure to backstop the "extension" to the original, misdesigned Lulzbot part. Then I built a dam that extended the shape of the original part. Next I filled the dammed area and let it cure. Finally, I carefully hand filed the top (active) surface of the extension to be coplanar with the original part.

Here is the switch approaching the newly corrected 3D part:
Image

If you compare this to the photos in the earlier post, you can see that the extension fills in the curved-off area in the original, misdesigned Lulzbot part that was causing the problem.

In this next photo the switch has just barely been actuated. You can see that the switch has some overtravel - standard for microswitches like this.
Image

When fully depressed, the switch actuator is just barely below the surface of the switch body. This means something needs to absorb the force of the switch body hitting the original, misdesigned Lulzbot part in case the stepper doesn't stop fast enough. That's why I carefully filed the face of the new extension to be flat relative to the original Lulzbot part; if the carriage overtravels, you want the force to be taken by the original part, not the (somewhat cantilevered) extension.

And thus, at full travel, we have this:
Image

Now the switch body touches the original misdesigned Lulzbot part, the latter taking the force rather than the new extension.

After taking these photos I reconnected the Mini and ran through a test self-leveling cycle without filament (due to the separate filament problem). Success! All four washers are now properly touched by the end of the nozzle.

So it appears there are at least TWO possible causes for the Mini's failure to properly touch one or more washers. The first is the low-quality stepper motors whose shafts are subject to breakage, as documented in other threads herein. This second failure mechanism is this badly designed 3D part from Lulzbot. I'm not sure how this ever worked at all, but at least now we know what was wrong and how to fix it even if you only have one 3D printer available.

Hope this helps someone... thanks!

mburko
Posts: 7
Joined: Thu Dec 21, 2017 11:21 am

Re: Lulzbot Mini requires huge maintenance

Post by mburko » Sun Nov 25, 2018 9:23 pm

Happy to have found this thread. My biggest problem is bed wiring. But first...

I too run a 4 Mini "Farm" with heavy usage. Each printer runs 12 to 22 hours per day. 3 PLA and 1 ABS. All were bought used. Serial number range from 1100 to 10500.

Generally satisfied with the Mini. I did buy 4 of them. Will probably buy more 1.03s or 1.04s and do the preventative upgrades. Not a fan of the Z-Belt design.

Now for my rant...

ALL HAVE BED WIRE FAILURES. On the 1.00 to 1.03 version units all wires have been removed from cable chain and long loops have been spliced in. So far so good. On the 1.04 only the probing ground wire is suspect so far.

Wires are cracking because the curve of the lower (bed) cable chain is too tight. Wires twist too much and crack inside the insulation.

Should have been fixed (re-designed) long before now. Wires should have a larger radius turn. Lulzbot solution is to fatten up the insulation to smooth the bending. Delays the failure. Is NOT a fix.

First clue was "Thermal Runaway" shutdown. Thermistor wires break and temperature reading drops suddenly. Firmware calls it runaway aborts the print and shuts off the power. VERY THANKFUL for that safety feature.

2nd was the bed wires themselves. Bed would not heat.

3rd was the Y endstop wires. During Z-probe belt would skip because limit switch wires were broken.

mburko
Posts: 7
Joined: Thu Dec 21, 2017 11:21 am

Re: Lulzbot Mini requires huge maintenance

Post by mburko » Sun Nov 25, 2018 9:28 pm

To continue..

The Y-endstop switches should not be on the bed. They should be on the frame. The wires too them should not have to move. When they do not move, they do not crack.

Thankful for the Open Hardware design. Modified both Y-rod holder designs. Now switches are on the rod holders. Wires are out of the cable chain and tied to the frame. Not as pretty.

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