UM2 Layers not sticking

[Nicolinux 288]

Hi,

UM2 noobness here again...

I have tried to print the grumpy pumpkin scaled way down to 1.5x. I noticed that the layers are not sticking to each other forming ugly gaps.

Printed with PLA defaults for the UM2, speed 50, layer height 0.2, shell thickness 0.8, fill 0.

By the way I had some small issues with the "Minicaltest" that came preloaded on the sd card.

On the right side is the test print that came with the printer (I wouldn't call this ideal, but ok). On the left side is the one I printed.

What's up with the lower part? It looks deformed, a bit thinner than the rest.

Ok, I am nitpicking here, the printer still prints very well and the accuracy is formidable.

But anyway, are there any tipps for improvement?

Thanks,

Stefan

 

[woofy 12]

Is the extruder motor cogging a lot?

I did a test print at 0.3 layer height, 50mm/sec and the motor was cogging continuously. There was massive under extrusion and the print was flimsy like straw with layers falling apart. I've not done a test at 0.2 but looking at the pic, it appears to be the same thing.

 

[Nicolinux 288]

What do you mean by "cogging"? I know the sound it makes when the knurled bolt slips and the extruder motor "jumps". Do you mean that? I didn't hear this kind of sound. Only once when I changed filament.

 

[woofy 12]

Yes, that's what I meant.

0.3 is 50% more than your 0.2, so maybe something else then.

 

[gr5 2,172]

Looks like underextrusion on that pumpkin. What temp were you printing?

The dirty "secret" of the UM2 is that it appears it only has about half the extrusion power of my UM1. So speed/temp/layer combinations that work fine on the UM1 are a struggle on the UM2. For 50mm/sec and .2mm layers I think you need 230C (I always halve the speed shown in my table that I generated for the UM2 because this table/graph was calculated with the nozzle printing in the air and on a part it prints even slower):

http://umforum.ultimaker.com/index.php?/topic/3418-um2-extrusion-rates/

Please try to over extrude on purpose - the easiest way is to warm up the nozzle to 180C or warmer and extrude manually in the air until you get the "click" sound from the extruder - if you watch it, you will see it jump backwards. Once you know what to listen for, if you are printing something and you hear a click, lower the feed rate to 95%. If you still here clicks, keep lowering until they go away.

edit: oh - and if it clicks on the first layer this is usually fine. That is usually just because the bed is a tiny bit too close. It's the rest of the layers that clicking indicates underextrusion.

 

[matengi 0]

Was the bed heated up?

To me it looks like a very hot bed and little fan. This causes the first layers to shrink gradually more, because the first layer sticks on the bed and cannot shrink, and for the next layers, the environment is hot enough to give the material the freedom to shrink as much as it can, within the limits that the previous layer sets. At a certain height the temperature fell fast enough to freeze the material early with little shrinkage.

If possible I would give it a try with lower bed temp.

 

[Nicolinux 288]

@gr5: UM2 PLA default temp at 220°. Thanks for the tip, will do it.

@MatEngi: The bed was heated up, again UM2 default (I think 75°). Fans were also at 100%

I find it weird to ignore the temperature settings (because they are stored on the UM2). I guess I got used too much to the old workflow. How do you guys manage it? Did you create many presets for all your filament spools you are printing with? And how do you select the temperature preset? Before it starts printing or while printing?

It would be useful if Cura could pull the settings out of the UM2 so they can be selected when slicing an object. A cool idea would be to store those settings in "the cloud" (manually on Dropbox) or on YouMagine. This way users could share print presets (another unique feature for YouMagine).

 

[gr5 2,172]

I guess I got used too much to the old workflow. How do you guys manage it?

 

I usually hit "print" and then click "tune" and set the nozzle temp to whatever I want for that part.

 

[illuminarti 18]

The UM2 workflow is very different, and it can be frustrating at first. At first it felt to me very much like the printer was inside a glass box, so I could see it, but not really interact with it. After a while that feeling goes away, once you learn to put up with a few irritations, and trust it to take care of everything else for you.

I'm still learning to get the best out of it - but all my best prints have been done at 30-40mm/s, with 0.1mm layers. Haven't seen temp to be too critical when the speed is fairly low like that. As George mentioned, I'm not sure that higher throughput rates (even rates that the UM1 was happy with) are the UM2's strong suit - but within its comfort zone, the UM2's output is stunning.

 

[Nicolinux 288]

A little update on this issue.

 

Please try to over extrude on purpose - the easiest way is to warm up the nozzle to 180C or warmer and extrude manually in the air until you get the "click" sound from the extruder - if you watch it, you will see it jump backwards. Once you know what to listen for, if you are printing something and you hear a click, lower the feed rate to 95%. If you still here clicks, keep lowering until they go away.

 

@gr5: I tried your advice just to get to know the sound. The thing is, I never hear it during prints. So the underextrusion must have another source.

I folowed Simon's advice and stopped printing calibration parts and went for things I wanted to have. But the printer still behaves weird. On the same print one part is printed flawlessly and the next one shows underextrusion.

The first part looks alright but on the second the UM2 decided to underextrude heavily. I made sure the filament spool isn't jammed and the filamen was unrolled so the extruder can pull it easily.

I printed another part (solo) and the problem is even worse:

 

Print settings:

 

• layer height: 0.2
  
• shell: 0.8
  
• bottom/top: 1.2
  
• fill: 15
  
• speed: 40
  
• temperature: 220
  
• bed: 75
  

 

Looking at the last part I noticed some dark spots on the outer wall. I am printing a dust filter now to rulle out this possibility.

But what can I try next?

 

[ian 32]

it couldnt be something to do with retraction settings ? the pla is being pulled back a little to much in jumps.. and then when the nozzle gets back to work.. it takes a few seconds for the pla to properly flow again ... ?

try for fun.. turning off retraction and see what happens..

if its not that.. make sure your extruder gear at the back is clean and there is no pla strings or anything clogging that up.

Ian :-)

 

[illuminarti 18]

Not to rehash it again, but I had bad layer prints like that quite often until I just took the filament totally off the back of the printer, and put it on the floor, behind printer, with several meters of plastic hanging coiled loosely in the air for the printer to feed on. I know you said that the filament wasn't catching on the infeed, but have you gone that far? Made a big difference for me.

 

[woofy 12]

Are you using the Filament Guide that snaps in the back on the UM2?

I tried that and abandoned that as it adds a lot of extra drag, especially on almost empty reels.

 

[gr5 2,172]

Those dark spots are almost certainly an older filament that was in there and FINALLY came out after such a long time. If those are ABS then that could definitely be related to the problem. The simplest solution is to just print even slower. It seems like you are having intermittent trouble either in the nozzle or with the feeder.

 

[Nicolinux 288]

Ok issue "solved". I upped the temperature to 230° and layers are sticking. I do see some gaps ocasionally but these may be due to other issues. I have also unrolles the filament and let it sit on the floor. Now the UM pulls it by itself - no spool involved.

@gr5: These spots are really thin fiber strands and dust. I saw them somewhere else too. I hope the dust filter will do its job now.