Z-Axis layer error

[neotko 1,417]

Yeah that play It's really weird. The others umo+ don't have that, maybe a little but nothing like that.

I tryed today to take out the linear bearings and they seem to move ok on the shafts. So I just applied one drip of sewing oil but the problem remains. I took out also the nut and it clearly has some play. I dropped a mail to the dealer I bought this kit so hopefully Trideus can give me an answer about this...

I tried to find the same nut on ebay/shops/etc but they are not like the one from ultimaker or they go as a pack with the z motor. Anyhow knows a trustworthy source to buy just the nut alone?

Edited December 27, 2015 by Guest

[gr5 2,172]

What country are you in neotko? I think the nut is a triple helix thread.

[gr5 2,172]

Just add weight to your bed. Lots of people have done this with the old wooden UMO and they were very very happy with the results.

[neotko 1,417]

What country are you in neotko?  I think the nut is a triple helix thread.

 

I'm in Spain. I bough it to Trideus BBVA.

I found the specs of the nut on the Ultimaker Bed Upgrade (not available on other githubs)

https://github.com/Ultimaker/HeatedBedUpgrade/tree/master/1187_Trapezoidal_Lead_Nut_(x1)

After googling for hours yesterday I found out that this it's a TR8*8 Trapezoidal lead nut. The think, it's that almost everywhere (even on misumi pages) the nuts ain't like the one from the um nemas, that must be because Ultimaker use Pololu motors.

Pololu sells the same exact nut for 6$ but I couldn't find any europe distributor for this. Also the ones I found (not from china) for example at reprapworld, they cost 5€ but the design it's slightly different. http://reprapworld.com/?products_details&products_id/1035/cPath/1655#.VoFnEet8_yk

So for now I'll wait for Trideus BBVA answers. Worse case scenario I will just buy one from Pololu usa and pay for delivery.

I been wondering also, that since I'll have one extra sooner or later, that with 2 nuts and some printed parts + a good spring, I could make a cheapo AntiBack-slash nut (two nuts, joined by a printed part and a spring from the top of a nut to the top of the other nut inverted).

If everything fails I'll try to put some weight on the back of the bed.

Edit: NVM found the pololu nut product number "2688" on an uk shop =)

Edited December 28, 2015 by Guest

[neotko 1,417]

Just add weight to your bed.  Lots of people have done this with the old wooden UMO and they were very very happy with the results.

 

How many have do that on the UMO+ / UM2 beds? Just wondering, since the bed on umo+ it's just the same of the um2.

[gr5 2,172]

I'm talking about the UMO with the wood bed - not the metal bed. I've never heard of anyone with a metal bed like you needing a weight. The UMO wood bed was so light weight that many people were able to eliminate this kind of thing by adding a weight.

[neotko 1,417]

Well. I'll change the nut as soon trideus give me a spare or the uk shop gets some stock. Thanks @gr5

[WTFockewulf 21]

Although I am trying not to be too enthusiastic about it, a guy in a german UM Facebook group pointed me to a possible solution of the Z Layer problem. Seeing it is a fix that can be tried within minutes I am going to share it.

First you clean the axis and the driveshaft of the z axis thoroughly and apply fresh grease to the driveshaft. What you then do is run the table to the top and unplug your Ultimaker. You then loosen these eight screws by about two turns and run the table gently up and down manually a couple of times (15 times in my case).

You will notice the motor and axis might move slightly. After moving the table a couple of times I tightened the screws again.

Not expecting much, I started the Benchy3D print. The silver one is before, the blue one after the "tweak" (cant even call it that)...

SInce then I have printed three objects that had a missing layer every single time... They are all perfect now. I guess its worth a try

[JohnFox 25]

That is very interesting indeed.

Looks like something out of alignment, most probably the stepper drive. I think the two pillars are quite tight fitting.

 

Although I am trying not to be too enthusiastic about it, a guy in a german UM Facebook group pointed me to a possible solution of the Z Layer problem. Seeing it is a fix that can be tried within minutes I am going to share it.

First you clean the axis and the driveshaft of the z axis thoroughly and apply fresh grease to the driveshaft. What you then do is run the table to the top and unplug your Ultimaker. You then loosen these eight screws by about two turns and run the table gently up and down manually a couple of times (15 times in my case).

You will notice the motor and axis might move slightly. After moving the table a couple of times I tightened the screws again.

Not expecting much, I started the Benchy3D print. The silver one is before, the blue one after the "tweak" (cant even call it that)...

SInce then I have printed three objects that had a missing layer every single time... They are all perfect now. I guess its worth a try

 

[WTFockewulf 21]

Short followup, printed a some parts for the fuselage of my Spitfire over night. These thin parts (red arrow, first 7mm two shells, after that one shell) always had a bad layer at about 13mm. These also turned out perfectly. I really think the problem is solved...

[peggyb 170]

Tried this tip, but it did not change a thing... the screws on the rods don't anything because the rods can't move, and the others are from the z- motor, and my problem are the bearings, I guess..... video on this page: https://ultimaker.com/en/community/18335-uneven-layers-although-i-print-at-1-mm-i-am-still-able-to-see-every-layerhelp-please?page=2&sort=#reply-129323

This is a combination of the play in the z-nut and some friction in the bearings. When the bed comes to a spot with friction it lifts the bed up until the play of the z-nut drops it again.

To proof this I put a weight of about 500 grams on the bed and printed the same file again.

right: without weight, left: with extra weight.

[lars-busack 0]

Hi guys I have the same problem with my UMO+ ...

This is the link to see my prints : https://db.tt/tmNDFxjU

Have you find a solution ?

Thank you

 

Hey, i have loosened the screws of both bearings that connect build plate and rods, ran the build plate up and down a couple of times and then re-tightened them in the area where most of the 'layer skipping' occured. That was a few months ago and it never happened again. Sorry for not being here such a long time!

[neotko 1,417]

Well for me the case it's closed, but there's still not perfect and printing at 0.06 seems to have a bit of trouble to easily move the table. Anyhow the nut it's one of the problems.

Today I got on the mail a new Pololu nut from a uk reseller.

Now. Check the wooble of the one I had:

 

And now the new nut mounted

 

Still I have some weird areas where the bearings stuck and also areas where the nut has some trouble to keep moving.

 

Anyhow I'm sure that with the replacements that Trideus sent everything will be just as my other two printers.

Anyway, the nut from pololu even though it should be the same, it's slightly different.

Left UMO+ nut. Right Pololu no wooble nut.

So if your nut woobles, get a new nut, it's just 5€. And the product code to buy it it's on the upper photo.

[Nicolinux 288]

Thanks! For reference, if you need it from Germany:

http://www.exp-tech.de/traveling-nut-tr8x2

[balden 6]

Hello all and first of all thanks a lot for all your excellent contributions and sharing your experiences, this is a great community.

I, too, am having the same problem: frequently (about 50% of prints) one or very few bad layers, always around the same height (10-15mm from the bottom). I have had this problem from the very beginning 2 years ago (Ultimaker 2 delivered in April 2014). Until recently, stupid me, I thought it was due to some "magical" underextrusion phenomenon that would only occur at a certain height. I even bought the extrusion upgrade partly in the hope it would solve it, but obviously it didn't.

I have read quite a few topics about this and found JohnFox's input (not only in this thread) very interesting and relevant. I think the root of the problem is not with the nut or the lubrication, it is indeed a problem with the linear bearings and the way they roll on the rods: other suggestions I found (lubrication, nut, Z-travel speed, weight addition) are probably only secondary factors that just help mitigate the fundamental problem with the bearings.

Here's my understanding of how it happens (at least in my case): when the print starts, the table lifts up and the bearings roll fine along the rods until they reverse direction: this is where the sticking occurs, about 10mm AFTER direction reversal, EXACTLY around the height where the bad layers happen. I disassembled rods and bearings from my printer and can reproduce this phenomenon by hand very consistently (there is a sticking for approx 6 reversals out of 10, and even a big sticking for approx 1 reversal out of 20). I have tried to degrease, clean, lubricate, everyhing: no matter how much effort, degreaser and lubricant I put, the sticking won't go away, it's just a little attenuated.

This sticking certainly feels like it's due to the balls jamming inside the bearings when they reverse direction. I really think that JohnFox is right when he says that the balls slide and skid instead of rolling which makes them jam, but curiously this only seems to happen shortly after direction reversal (one also hear a faint clicking noise of balls piling up against each other when jamming, which some on this forum described as "like sand in the Z-screw mechanism"): after the sticking point is passed, I can distinctly feel (and hear) the balls rolling again. I have also noticed that the sticking point is clearly more frequent and more pronounced when the bearing slides vertically: probably the bearing's own weight is sufficient to better press the balls against the rod and prevent the skidding when sliding horizontally.

So right now I am strongly suspecting a quality problem with the bearings design and looking for good quality replacements to see if it makes any difference. My current bearings are marked "LM12UU". I found JonnyBischof's advice about the Misumi brand and ended up with their reference "LHFSWF12G": can anybody please tell me if this is the right part or otherwise point me to the good one (or advise another trustworthy manufacturer)?

Thanks in advance.

[neotko 1,417]

https://ultimaker.com/en/community/18394-sounds-like-theres-sand-on-the-z-screw#reply-135067

Also Igus has a square flanged earings that fit perfectly (at least the step file) but they cost 38€ each because they are bearin-less.

[neotko 1,417]

Btw I agree somehow. But also if you have a bad nut but the bearings are perfect there's no issue. So it's a mix of stuff but ofc the best think it's to have booth parts just perfect. With a perfect nut the z jumps disappear immediately because there's no room for the bearings to stuck since the z motor has more that enough force to move them, but when the z nut has a good mm of playroom, then if the bearings ain't perfect then it's very easy for the z to stuck at some points unless you artificially make the bed heavier.

[balden 6]

Thanks a lot for the link neotko. I laughed when I read chrisw's post about being unable to stop the Misumi bearing from rolling, even holding the shaft horizontally: my current bearings are definitely very very very different, even when I hold the shaft vertically, the bearings will not slide all the way under their own weight without sticking somewhere halfway.

I agree that everything must play together but I was just saying that the root cause seems to be the bearings (at least in my case and for this particular problem of banding aroud 10-15 mm from the bottom). I may well end up adding a little weight to the platform, too.

Edited June 16, 2016 by Guest

[balden 6]

OK here's some feedback about this. After the previous exchange, I gave my stock bearings another serious run of manual exercising, WD40 cleaning and degreasing cycles. Indeed one can feel the situation slowly becoming better, but it's a pain because it really takes a long time and a lot of patience. Following other advice in this thread, I also decided to add some weight (about 1 kg) between the pillars, which brought a big improvement. After that, I have been able to print the visually highest quality parts ever with my printer.

However, since the bearings are still slightly sticking around Z=15mm, and since I seemed to notice some faint residual irregular layers, I decided it would be worth to attempt to replace them with higher quality parts. Unfortunately it seems impossible to order Misumi bearings as an individual, so instead I chose to order a couple of (costly) Igus polymer bearings referenced in the other thread. In short: don't do this, don't go for Igus, it's a mistake. While the Igus bearings feel about fine when you slide them manually, they also generally have more friction than the ball bearings, and they have it all the time, not just upon direction reversal. The result (still with additional weight on the platform) is that they make the problem worse: slightly irregular layers all the way, which is especially noticeable on 60 micron prints.

Also, be aware that the Igus bearings are not a perfect fit for the UM2: they have a much thicker base which would require longer screws for a good hold (with the stock screws they hold on only 2 screw turns which does not feel sufficiently stong), and they have a slightly larger outer diameter of the casing (+1 mm) which makes them not fit in the hollow inserts under the hood. Besides this, while the parts look very pretty with anodized aluminium dark grey finish, they seem rather grossly machined so their actual "quality" is not evident to me (considering the price).

So after I realized my mistake, I disassembled the Igus bearings and mounted the stock bearings back, after yet another run of heavy exercising, cleaning and degreasing. This is where I am today. Honestly the quality of the prints with this setup is highly satisfactory, but I'm still wondering if you guys know any way to buy those Misumi replacements: do you know resellers who accept to sell those parts to individuals? Thanks in advance for any advice.

Edited July 9, 2016 by Guest

[neotko 1,417]

Nice info about the igus, and too bad they suck! Sorry I don't know any misumi reseller..

[gr5 2,172]

Sorry to change the subject slightly - I was at the Utrecht protospace (a makerspace) last week and they had a UMO that had some ugly layers. I didn't have much time - I just took a paper towel and held it against the Z screw while moving the bed up and down 10 times - sticking the paper towel into the thread as much as my thumb nail would allow. This was about 5 minutes of work. I only did the top half of the Z thread because the UMO goes up to home, not down and my part was small. It didn't fix it entirely but made a huge improvement. Sorry that the filament colors are different - in real life you could clearly see it's better:

[balden 6]

Hi gr5. I think this is the same symptom here: in my opinion this phenomenon always revolves about the same factors :

- slight play in the Z-stage screw/nut (probably almost unavoidable at 60 micron scale)

- friction in the linear bearings (especially upon direction reversal after ~ 10-15 mm)

My understanding of the phenomenon is as follows: depending on the variable friction and sticking along the rods, the Z screw/nut is EITHER retaining the platform from falling OR pushing it downwards, the Z-difference between those two conditions being the screw/nut play. Goo in the Z-screw threads will probably increase the susceptibility to friction and lean towards the "pushing" state. Adding weight to the platform, cleaning the Z-screw threads and optimising the linear bearings leans towards the "retaining" state. Irregularity in the layers results from transitioning between those two states more or less randomly during the print.

In my experience, once the balls get rolling inside the bearings, there is no more friction and the rest of the print goes all right (unless there is some serious goo in the screw threads).

By the way, the weight addition definitely works great on the UM2 platform: I followed your original advice for the wooden UMO and it clearly made a huge difference also in my UM2. My initial guess was that the weight should be ideally added right between the pillars to avoid inducing significant bending moment on the mechanism, so in my printer I added it under the hood on both sides of the screw (there is not much space in front of the hood anyway). However, I must admit that I'm not entirely sure that it would not be even more favorable to also deliberately add some bending moment by putting the weight slightly forward of the pillars: indeed, when I manually manipulated the linear bearings, I noticed that the friction/binding phenomenon upon direction reversal was much less likely when manually exercising slight bending force between the linear bearing and the rod.

Supposedly, a slight bending force puts a non-zero load on the bearing and may help prevent the balls skidding and force them rolling... but of course this is only the way I felt it when manipulating my own stock bearings (which were definitely not the best out there). Probably there are specialists out there who have more clues about how linear bearings operate when there is no load on them (ie when they are set up to travel vertically under negligible bending moment as in the Ultimakers). One could also try to tilt the printer (10 or 20 degrees backwards?) while printing.

Edited July 9, 2016 by Guest

[gr5 2,172]

Or you can print upside down. But it's more complicated if you always print upside down (e.g. nozzle purge at start of print is messier!).

[mattnaples 0]

The Z bearings require Lithium grease, I have been having this issue on again off again for over a year. My Z bearings feel fairly terrible sticky and gravely. I am going to try to clean them out with WD-40, then re-grease with white lithium grease. Will let you all know my results.

The bearing info was found at: https://us.misumi-ec.com/pdf/fa/2012/p1_0265.pdf

Hears to hoping this solves my issues!