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taxez

Z-Axis layer error

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Hey guys, I'm having a problem with my U2 that I can't seem to get my head around. After an extended period of inactivity my printer has started producing inconsistent print errors in the z-axis.

ycsFYb2.jpg

It's especially bad when printing with ABS as the tension/warping causes the printed parts to actually split along the seam. It seems that at times during printing a single layer doesnt extrude correctly or the heatbead lowers to far, leaving a larger gap. I witnessed the error on several pla prints at about 11mm height. With the abs print shown in the picture above the error occured at 19mm height.

Has anyone ever encountered such a problem with their U2?

 

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Hello everyone,

i have experienced a very similar problem. As for me, my Ultimaker Original+ seems to occasionally skip a layer oder two after 10-20mm of printing.

Not on every single print, though, but enough to be annoying.

You could check the following steps and see if one does the trick for you.

- I have checked for filament under-extrusion, which is not the case.

- I also added a fan to actively cool the electronics board (19-24V Fan Pins),

which also did not get rid of the layer skipping.

- I re-lubricated the z-axis very, very well with the supplied MAGNALUBE.

Though this can't do any harm, it didn't fix the issue either.

- As I read in other threads, the current setting of the z-stepper driver can be lowered to something near 900-1000 mAh, which can be set in the UM2 Controller, BUT NOT on UMO+, as there are trimpots on the UMO electronics board which can be trimmed to a lower value.

Unfortunately, my UMO+ was deliviered with a newer electronics board (the white one) which neither seems to have trimpots, nor UltiController settings. :(

Could someone think of a way for me to adjust the stepper values? I think this could really be the solution... Or maybe I just did not find the trimpot/setting?

I will add pictures of my electronics as soon as I return home.

Best regards, Lars

 

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These gap layers are often caused by a tangled filament that repairs itself. But you are likely correct that it is mechanical. There is almost zero chance the problem is electronic.

Sometimes a z screw looks and seems perfect but has a fault. Same with the 2 rods and bearings and the Z nut.

I would run the platform up and down with the power off (UMO you have to spin z screw by hand but UMO+, UMO HBK, and UM2 you can just push up and down on the bed. See if you can get replacement set from UM (all the parts - rods, z screw, z nut, motor).

 

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Thanks for the quick reply!

What dou you exactly mean by "tangled filament repairing itself"?

Something caused by too-cold over-extrusion? I checked the filament for grinded spots: not the case. I have printed 2.85mm filament at 100% flow at 210°C at 50mm/s with 0.3mm nozzle.

Besides, I could swear that the z-step makes a slightly different clicking sound when skipping a layer.

I moved the platform up and down carefully and there seems to be a spot

where there is a significantly higher friction, but this is about half way down.

Maybe rod alignment?

Also just noticed that the wooden cover of the Z-axis bearings got loose!!!

By its internal tension, it now touches the back of z-rods and and z-screw:

ECsYOOl.jpg

I assume there could be a tiny chip of wood in the screw thread.

Will clean it with a toothbrush, then re-lube and report back...

Obviously, wood chips won't happen on an UM2, but this might be something to check anyway. :)

 

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> These gap layers are often caused by a tangled filament that repairs itself.

Where does the filament get tangled and would there be a way to avoid it getting tangled?

Does anyone have any idea what I could try? I feel like im sitting on 2k worth of trash as of right now :(

 

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Sorry you feel that way Taxez. I have had problems on and off with my printers but over all I love them. They are working great for the last year.

It's confusing that two different people are posting similar but possibly completely different issues here.

Taxez it would help if you posted every day instead of only once every few weeks as it's hard to remember everyone's issues.

 

Where does the filament get tangled

 

on the spool itself. Sometimes you can purposely tangle it - wind the filament on the spool but purposely run the filament *under* a thread of filament in a lower layer. Then try unwinding it - it's tricky! Hopefully you aren't in this condition but its VERY EASY to get in this situation and the only fix is to remove the filament from the machine, unsppool several meters and fix any of these that you find.

This is just one theory - there are many things that can cause a gap layer. The filament tangle is by far the easiest to check as you can just unspool some filament and realize it's stuck. Somewhat.

Another theory is that the temperature dropped on that layer for some reason - seems unlikely as it appears to only happen once in the entire print - usually changing temperatures only happen on a repetitive bases every few minutes. You can verify this is not the problem by watching the temperature carefuly in the TUNE menu while printing and make sure it stays within 1C (or maybe 2C) of goal temperature while underextruding the bad layer.

The third theory I have (these are all things that happen to people all the time on this forum) seems to me the most likely and possibly the most difficult to prove - it's that there is something sticky or wrong with the Z axis where it moves a little bit less than it is supposed to (say .19mm instead of .2mm on each layer) and then suddenly it finally catches up and drops 2mm all at once. Something like this. Because something is sticky maybe in the Z axis. You can test this by pushing the bed up and down and trying to feel for a bad spot. You can visually inspec the Z screw - also look for it warping. But the best test is to print a few different parts - preferably a 10mm square tower that goes the same height as the print you already printed to see if there is a gap layer. Then print another one 15mm square to see if the height is *still* the same. If 3 out of 3 prints hafe the same problem at THE EXACT SAME HEIGHT and the 3 prints are all different sizes (different amounts of material on each layer) then the problem must be related to Z screw or Z nut, or Z bars and you can have Ultimaker send you new ones. It might be as simple as adding some grease to the Z screw (in the green plastic container) and some light oil to the z rods.

 

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Thanks for your extensive reply gr5. So far I've always managed to solve any problems with my printer. Overcoming issues and tinkering is part of the fun... as long as there is a solution in sight. My frustration caused me to be a little overdramatic.

So far this bug has been very illusive. Some prints indicate a certain z-height at which the error occurs. The open dive print shown in the picture above actually had two broken layers. The second one occuring several hours after the first. None of them consistent with with the location of previous errors and what is most frustrating... unless I sit infront of the printer for 8 hours... hard to wittness.

At least I have somewhat of an idea what to specifically look for. I'll see what I can find out during the next few prints.

Thx again.

 

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Hi Taxez,

in my case the layer skip happens occasionally, but quite consistently after 10-15mm height. I cleaned and lubed my z-screw over and over again, but i could still feel a resistance everytime i moved the z-nut over this area in the thread. Therefore i suspect the screw thread itself to be defective and i will contact UM for replacement.

In my frustration, i moved the z-table up and down at least a hundred times, thoroughly cleaning and lubing with toothbrush and magnalube after every ten up/downs or so. I was hoping to flatten the scratch by repetitive movement and although the bug still occurs once in a while, it seems to fail less frequently now.

I absolutely do not advise anyone to do this!!!! As i said, i was frustrated, but at least it did not get worse... For my issue, i was able to narrow down the possible causes to a fault in the thread. Worst cause, i guess. If someone has useful info about how to inspect and repair flaws in the z-screw (if possible?), i would be glad!

For example: Would it be a good idea to completey clean the screw and nut with alcohol and then put fresh grease overall? I'm running out of options here and to be honest, i don't want to give up the z screw yet... :smile: in other words, until the replacement arrives, i would like to have tried everything i could.

By the way: Although i believe the problem is mechanical, i tried raising the z-stepper acceleration to make sure the stepper gets enough zing to overcome any friction. Yes, i am beginning to treat my z-thread like crap now... :grin: Well, no further improvement so far, but as the firmware default was at the lowest possible setting and could only be changed in steps of 100, i only dared to double this value to 200. Maybe, i will raise this a little more the next time i get upset again...

Even if you don't have any problems with your z-steps: Should you ever get bored of the sound your z-motor makes when homing, etc., the z-acceleration value is the one you might wanna tinker with... :wink:

UPDATE: Just set the z acceleration to 300. Nice sound. :) Still skipping layers between 10-18mm height... :(

 

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I've always had an aversion to manually moving such seemingly delicate parts. So I rarely did it. However In my case I just noticed the z-screw moves as if it had sand on it! Especially towards the top. Come to think of it I've only had the z-layer issue since I relubed the screw a few weeks back. I have no idea what went wrong as I used the supplied Magnalube in the way I was told to. But I hope properly cleaning and applying new lubrication will fix my problem.

 

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However In my case I just noticed the z-screw moves as if it had sand on it! Especially towards the top.

 

Yeah, same here! Its a slight grinding sound near the top of the screw.

Maybe a diiferent lubing technique such as full-dipping the top of the screw in machine grease might help, but i don't have such an amount right now and my toothbrush-application just wont' do the trick...

I'm looking forward to hear about your WD50 results! Stupid question: What's the difference between WD40 and WD50? i only got WD40 here (and i think i never saw a store in schleswig-holstein selling WD50)

 

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Well, you intend to use WD-50 as a cleaner, not as a lubricant, right?

I don't believe WD is up to the task of lubing the z-screw and it might be too aggressive as well.

I use Nigrin Light Silicone Spray for all rods, but i wouldn't dare to to put it on the screw thread,

as it's too thin to withstand the forces between thread and nut, making the thread quality even poorer over time. also, it's quite volatile and tends to run away from where it should be sticking...

But i am only an amateur and i'm guessing as always. Maybe someone around here with more profound knowledge of lubrication physics/chemics?

 

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Sorry that was a typo. I meant to write WD40 but it was very early in the morning. And you are correct I am not planning on using it as a lubricant. I want to clean away the old grease which I assume is covered in dust/dirt and reapply some propper CRC Multigrease to the Z-screw.

I'm hoping for the best, but I fear two things: 1. Having to take the entire printer apart because I can't reach the Z-nut and 2. It's not an error with the Z-axis but with the filament feeding and having to modify the printer in the following or similar way http://www.thingiverse.com/thing:430899

 

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If you feel the same "grinding" at the top of the z-thread as i do, i assume your problem isn't underextrusion.

i have upgraded my UMO+ Feeder with double helical gears which dramatically improved extrusion/retract reliability (because the teeth of helicals gears are always touching each other, directly translating the e-stepper motion to the filament.) i don't know if this upgrade is available for UM2, but was worth 6 hours of printing :)

again, i don't know how this applies to UM2, but on my UMO+, there are 2 screws underneath the milled aluminum platform. when i remove these, i can move the (in my case: wooden) cover upwards, away from the platform and then reach the screws of bearings and nuts. so i would only have to remove the z-stepper (with z-screw) and get the wooden cover off the platform instead of disassembling rods and platform completely.

1rIt9Jr.jpg

Yu2lbMO.jpg

RlLMIr8.jpg

I hope this is of any help... I guess the UM2 has a different assembly, but maybe it's similar enough...

 

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It's very similar on UM2 as it has the same 2 Z bearings and the same Z nut and screw.

That sand noise is ball bearings falling down. It's not a problem. The ball bearings are in the 2 side linear bearings (the z nut has no ball bearings). It would really help to loosen the screws on the side bearings to see if maybe they rods are bent slightly and you get a stuck spot. This could move your problem spot by loosening - moving the bed to the problem area and retightening.

I'd hate to see you get a new z screw from ultimaker only to find the problem is actually in the 2 side rods.

 

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Thanks for the info about the assembly. It will most probably come in handy down the road.

So after another frustrating day of tinkering I'm still clueless. I printed a simple one layer thick cylinder to test the z-axis behaviour.

7HdvbP2.jpg

There are some fuzzy particles around the edges but all 110mm worth of layers extruded at 0.1mm each on top of one another without any signs of under extrusion or skipping.

So I jump onto an object I want to print and after a few hours of printing it turns out like this:

5bEonAX.jpg

47cac6a1d12035c0b63f37ffaa7572e55f4e5f5e4f710abce37eaec02b9feae5.jpg

I'm left guessing its a problem with the filament feeding. Come to think of it this only really started occuring after I adjusted the retraction settings to remove stringing. This printed at 45mm & 25mm/s retraction settings. I went through some of my old prints and actually found patient zero. The first print that started acting up.

kNIFwWC.jpg

The faulty layers are cearly visible at about the same height. It's hard to imagine this being a random error with fillament grinding, entangling or something else. Unless the someone can make sense of what has being going on my next step will be to flash the firmware of the printer and restore all screwed up settings to factory presets.

 

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Good day, good sirs,

i suspected the retract settings as well ( i like to use 4.6mm at 37mm/s ), but then i printed a pair of race vases. No solid Bottom/Top, no infill, 2 perimeters, 190°C, 0.1 layer, 50mm/s. Two of them with and two of them without retract and both were printed flawlessly, aside from stringing. Will try to verify that this wasn't just luck.

happens more often with prints that have large X/Y scale, it seems to me. maybe you could print another dummy cylinder with, uh... D=100mm and H=30mm? so it's more likely to get the "desired misbehavior". i will try this in the evening and report back...

oh, since i had already taken apart half my build platform yesterday, i thought it could do no harm and unscrew these rod bearings. i must admit, it was no pleasure retightening them with the wooden cover and X/Y motors in the way and therefore i couldn't retighten them exctly in the friction area, as this area is all the way up the z-screw and up there the hex key interferes with the wooden cover... :) well, at least i tightened them mid-way. during initial assembly, i might have tightened them with the platform all the way down, but i'm not sure.

But VOILÀ! Significantly less friction and "sand" sound. Oddly, i have to reset the z-stop, because the cover is in place somewhat different than before... Minor issue, will fix it in the evening and do a 5 hours print to see if there's less z jumping now.

gr5, if you were right and the rods have actually been the culprits, i would like to buy you a drink next time i'm in boston!

 

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Let's assume the rods where my problem. I wonder how they became bent over time.. seems implausible to me. Do Ultimaker themselves actually offer some kind of support in such situations as mine? Actually considering selling the printer as broken and cutting my losses. Real shame.

 

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I can't imagine how the rods could have been bent in your machine, as it came preassembled... But actually, they don't need to be bent to cause malfunction, i guess...

As i assembled the UMO+ myself, i must have somehow put the rods not perfectly parallel and then tightened the bearings screws in a bad position or something like this. i will measure the x-distance of the z-rods with calipers (top, middle and bottom distance) as soon i return home. maybe you can do the same to check if the are really perfectly parallel.

nevertheless, i still assume my z-screw isn't perfectly smooth either, and will keep an eye on this issue. i will let you know any results...

 

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