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Dim3nsioneer

Horizontal banding on UM2

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Hi there

When I printed a cylindrical object today I realised I have significant horizontal banding. Thus I printed Nick's test object for http://umforum.ultimaker.com/index.php?/topic/3755-horizontal-banding-elimination-thread/.

And this was the result:

banding white PLA

It's printed in white PLA at 220°C / 50mm/s (or even a bit less due to minimum layer time). X/Y-acceleration was set to 1000mm/s^2; x/y-jerk was 20mm/s. I use Robert's feeder which works flawless so far. The print was sliced with Cura 14.07. Ultimaker2Marlin is up to date.

To cross-check, I printed the same object with the very same parameters with blue PLA:

banding blue PLA

 

The banding is much less pronounced but it still can be found on a closer look. So the two filaments do not behave exactly the same. That's fine with me as long as they behave well... However, the lines are not at the same heights; they seem to appear randomly.

 

Then I realised my UM2 has some vertical play between lead screw and the trapezoidal nut; it's maybe half or one mm.

My question: Do other UM2s also have play there? I remember one of Nicolinux' machines to have had plenty of play there... If fear that the platform hangs sometimes and then gets free again; something I know from the old lead screw of my UM1.

 

If there are any other reasons for the horizontal banding someone might think of, please also let me know...

 

thanks!

 

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That kind of "banding" looks to me rather a consequence of the pretty high speed you are printing at. I can bet that if you are patient to try at 20-30 mm/s it will disappear. It is also that artifacts are more visible on white (with "adequate" lighting) than on colored material.

 

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I continued on this issue and switched to a Sky Blue filament which seems to show the effect best.

In the meantime I got a new z nut from Ultimaker as the old one showed some significant play in all directions. The new nut hasn't got the play but doesn't solve the case neither.

The following picture shows three test prints. From left to right: old nut, new nut, new nut without fans.

Horizontal banding on my UM2

 

The print settings were: The=210°C, Tb=60°C, 3731mm/s.

Obviously the filament is very sensitive to cooling compared to other colors. Shutting the fans off is not a solution as I got a very nasty line spacing at the top fill.

I already tried:

- Increasing flow by decreasing filament diameter settings to produce rather over extrusion

- Higher (220°C) and lower (205°C) temperature

- setting up new PID parameters for the hotend (achieved stability +/-1-2°C)

Nothing of that worked...

So I'm open for new ideas... :???:

 

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http://umforum.ultimaker.com/index.php?/topic/5066-u2-z-ribbing/

I don't really have much faith in me bugging ultimaker for a new z nut because you seem to still be having issues. I just lowed my z max speed to 20mm/s but haven't gotten a chance to test if that helped it at all. As you can see this isn't a new issue for me and it seems to boggle everyones mind because I haven't had any replies.

 

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@Yellowshark: Thanks for the link. It's a quite nice summary of all possible effects. It might be worth to include it into the troubleshooting guide at some point. However, I'm aware of all these effects and I'm pretty sure that one of them is indeed the case for my issue. The thing is, I'm using really high-quality filament (Diamond Age) with very low fluctuation of the diameter (1-2um). But still it might be these fluctuations. Next thing I will do is to repeat the print on the UMO with settings as similar as possible.

And what could I do if it is the leadscrew itself? On my UMO, I replaced the leadscrew with a ballscrew and really got rid of such effects. Unfortunately, I can't use a ballscrew in the UM2 as there is no space for a coupling between a standard NEMA17 motor and the ballscrew (due to the fact that the print bed goes really down to the bottom).

@Mikey: Lowering the speed is a work-around but no solution IMHO. And in my case with this exact filament it does not make the banding disappear completely. I'll let you know when I have the solution...

 

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I suspect you are just printing too cold and too fast. Since you don't want to lower the speed, I would raise the temp to at least 230C. Maybe even 240C (but no hotter).

 

So you are just thinking we are having extrusion problems because it isn't flowing through the head evenly? Could it have to do with how high the ptfe coupler is?

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This is just a small update. I printed the same model on my UMO yesterday using as similar settings as possible.

This means: print speed 31mm/s (I wrote a wrong number yesterday which I corrected in the post above), T0=210°C, Tb=60°C.

Left: UMO, Right: UM2:

Horizontal banding UMO vs UM2

I don't know where the holes on the UMO print come from; it might be an artefact from printing XT before that print; I'm investigating at the moment. However, the important thing is, that there are some fluctuations in the vertical surface but no real banding as on the UM2. So this test gives an idea how much the diameter fluctuation of the filament or some other filament related reason can influence the print quality. btw: I have a ball screw on the z axis of my UMO.

 

I'm currently printing the hbc-testprint on the UM2 again with 230°C. It's just a few mm printed but I can already say that the banding is well visible. I'll post a picture when it is finished.

However, I think it is not completely wrong to see some correlation between temperature, speed and print quality. gr5's remark triggered some thought I want to test: How much does the temperature of the already deposited material at the time of the next layer being printed influence the quality? I'll test this by speeding up the print by a factor of two.

 

edit: This is the result of the temperature variation: 210°C, 220°C, 230°C (from left to right).

horizontal banding UM2 at temperatures 210 220 230

It's obviously not the way to go as Diamond Age PLA likes it rather cool than hot.

 

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Going left to right it looks like it gets more underextruded. Are you sure you weren't just printing faster? I've printed diamond age at 240C no problem. But it was purple/grape color. I guess I have no idea what's going on here and should shut up.

 

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Going left to right it looks like it gets more underextruded. Are you sure you weren't just printing faster? I've printed diamond age at 240C no problem. But it was purple/grape color. I guess I have no idea what's going on here and should shut up.

 

No your ideas are helpful and they spark thoughts please continue to help. My following question is this. Should I be setting layer heights to be something like .06 vs.05 and.16 vs. 15 I know there was something about setting the height to be a multiple of the thread screw pitch/size but I thought the U2 had a screw that would allow any height?

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Going left to right it looks like it gets more underextruded. Are you sure you weren't just printing faster? I've printed diamond age at 240C no problem. But it was purple/grape color. I guess I have no idea what's going on here and should shut up.

 

'Shutting up' would be the worst thing you could do... :eek: It's always very helpful to have unbiased meanings and new ideas for solving complex issues.

Although I have not enough 'grape' filament to test it I'm pretty sure it will look much better. I made a print with 'Cherry Red' on the UM1 to compare with the print posted above and it looks quite perfect. So it's really a question of the color (the master batch used). You can also see in the first post that it is much more pronounced with pastel colors.

But I agree with you. It looks more and more like underextrusion the higher the print temperature is. I can assure you I just changed the temperature at the UM2 and used exactly the same gcode and the same settings for everything else. btw: I'm not sure how exact the nozzle temperature is on my UM2. I had several cases which indicate that the actual temperature might be higher than the value measured. However most of the prints don't show clear evidence for a too high temeperature. I'll have to test this one day.

 

The left one looks very much like ribbing produced by layer height vs. leadscrew pitch.

 

Not exactly. I have the impression the pattern is not regular. And if you look closely you can see the same effect also on the other two prints. It's just superimposed by this underextrusion-looking-effect.

So I tried a print with double the speed. And it really got worse. But I have to look at it closer to see if the banding also got worse or if there are just more irregularities due to additional vibrations. But it's good to know settings which makes it worse. Like this it's easier to see if certain actions taken show an effect.

There is one part which I would exclude as origin at the moment and this is the lead screw. If there is something wrong with the thread the banding should show the same pattern for every print, right? I'll test a special anti-backlash-nut for the lead screw but it has yet to arrive.

 

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Some intermediate update. As gr5 remarked two days ago the prints looked more and more underextruded when temperature was increased. Diamond Age Solutions confirmed that their filament usually has to be printed rather cool but some colors even cooler or at a higher flow.

Indeed I got rid of the 'underextrusion' by printing with the same settings but 195°C at 31mm/s:

 

horizontal banding UM2 195C

(it's now the 'pure' banding)

The really remarkable thing was, that I could achieve the same quality at 210°C with 0.2mm layer height instead of 0.1mm.

 

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1) Can you get a better picture of that last print?

2) Could it be that the PLA changes color depending on temperature and your nozzle PID controller is having trouble keeping the temperature consistent?

 

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I have a print I'm keeping in the back for now because it as a lot of banding in it like this. My guess is oil. I'll get some asap and print again to see the difference. Mine is printed in UM White PLA and its not a change in color. I had a case of color change on a very long print with UM Silver-Metallic PLA and the surface was still very smooth.

 

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@pm_dude: Everything is perfectly oiled as a Bodybuilder's body... ;) I can move the print head with my small finger...should be ok.

I even replaced the grease on the z axis. It has definitively something to do with the z axis the structure are actually rings and not micro-shifted layers. I'm now waiting for this anti-backlash nut...I really don't like whatthe stock nut looks like btw: I already tried it with some additional weight...didn't help.

@gr5: What do you mean by 'better'? Higher resolution? Yes I can do that... but it's not blurred or something, isn't it? And as mentioned some posts above I already adjusted the PID settings. Temperature is stable up to 1-2°C. And it's not just a change in color but really rings with different radii.

 

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Did you try to see if printing at different place on the build plate will change the result (center vs corners, back vs front)?

 

I did a test print at the front left corner. Looked very much the same as in the center... but was worth trying...

 

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. It has definitively something to do with the z axis the structure are actually rings and not micro-shifted layers. I'm now waiting for this anti-backlash nut...I really don't like whatthe stock nut looks like btw: I already tried it with some additional weight...didn't help.

 

Ah! Then it's probably Z axis. Or belts too loose - make sure the belts are all tight. Especially the short belts. If the XY belts are loose then I would expect different layers to stick out different amounts depending on where the Z scar is and depending if the head is travelling clockwise or counter clockwise.

 

@gr5: What do you mean by 'better'? Higher resolution

 

Yes, more focused higher resolution - or just cropped closer to one of the problem areas. I can't tell in the photo if the plastic actually changes color, if there are tiny tiny holes (underextrusion) if layers stick out (now you say they do) or what it is that is different on different layers. But it sounds like you have layers that "squish" out because Z moves too far on some layers and not enough on others. This is more common on the UMO as the UM2 has a much better Z screw/nut combination.

 

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Did you recheck the image? I uploaded it in full resolution. I think it's quite visible a the sides that it's not just a different color but different radial positions of the layers.

Yes, I know the effect from my UMO (I got rid of it when mounting a ball screw on the z axis). I actually don't like the stock z nut of the UM2 as the thread is quite short. Any uncertainties in production lead likely to significant play (the original nut had about 1mm play IN EACH DIRECTION(!), the replacement has not).

At the moment I don't know how sensitive this special filament is to temperature fluctuations. I will do some test about this within the next few days. I just saw that Daid did some changes to the PID code in firmware 14.09.1. I still have 14.07 installed. I will upgrade it.

btw: How stable is the temperature on your UM2?

I recently had to remount the x and y motors to an exchange of the 5/10/25mm spacers on both axes (the belts were rubbing at the pulleys and the black particles were ruining some prints). As I know how important the tension of the belts is, I made sure the short ones are tight. The long ones have their automatic tensioners anyway on the UM2. Every belt is now running smoothly.

 

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