underextrusion during printing at random height

[edis 0]

Hi,

I'm constantly having a problem, that some random layers in my print looks like underextrusion. E.g. all walls are smooth but suddenly i get single layer which has a lot of holes and it weakens my print a lot...

This particular part was printed with such settings:

Temp: 210C

Speed: 60

Fill: 100

Fan: 255

Here's some pictures:

I've checked this on different parts and the height differs, this underextrusion varies on different parts. Sometimes i get perfect prints, though most of the time i use the same settings.

Here is another part printed with same settings, but no visible layers difference:

Any ideas what could cause this? Since it differs on each part, so i would throw out z axis wobbling or bended leadscrew..

 

[illuminarti 18]

I'd look carefully at your spool of filament, and make sure that the plastic is always coming smoothly off the reel, without the extruder actually having to pull hard on it. I've seen exactly this problem where the plastic would get just slightly caught on itself on the reel and not unwind smoothly. Try watching the print, and manually unwinding a few loops of plastic every few minutes, so there's always loose filament available for the extruder to pull in, without it ever feeling any resistance, and see if that makes a difference.

 

[edis 0]

Thank you for the tip, sounds like a possible solution

 

[edis 0]

I've tried unwinding the spool while printing and no effect. Here's a result:

 

Got similar results when printing yoda:

 

 

Finally i thought that it might be a extrusion issue. I have a custom made hobbed bolt, my steps per E is 794.4. So i've tried printing some hollow boxes with different fill settins.

From bottom to top:

1. 80% flow

2. 90% flow

3. 100% flow

4. 110% flow

5. 120% flow

 

so to me looks that this fill setting doesn't really do much changes. My steps per E calibration also showed that the value there is ok. E.g. i give command to extrude 10mm of filament and it gives 10mm.

 

Any suggestions what else could be causing this? i have a dust filter on my filament, it collects quite a lot of dusts.

 

[gr5 2,167]

UM1 or UM2? Either way it sure looks like you are printing too fast and cold. Either raise the temp by 15C or slow it down by 30%.

60mm at 210C and .2mm layer height (what is your layer height) is quite doable with most filaments but I'm going to guess that this black filament needs a little higher temperature. So try 225C. Or 40mm/sec. I suspect you'll see a huge improvement.

Also your extruder might not be as powerful as it should be. On the UM Original it should be able to pull 22 pounds. Consider testing it by unlocking, pulling back a foot of filament, relocking and turning the gear with one hand while putting 10-20 pounds of weight on the filament pulling downwards with the other hand. The spring should be compressed (when the mechanism is closed) to about 11 to 11.5mm. Maybe give that screw a few turns tighter.

Also remove the pla and shine a flashlight onto your hobbed bolt. Is there any plastic in there or something causing problems? Is it lined up with the slot properly? Maybe post a picture and also a picture of your extruder when it is clamped closed.

How about the black wheel that the filament presses against. Does it turn easily? Did it get worn down and does it now have a flat spot in it?

Also you could have a partial nozzle clog but I doubt it.

 

[illuminarti 18]

In the latter tests, I'm seeing less of the one-or-two-layer under extrusion, and more just general scrapiness in the layer alignment. Looking at the test blocks, you can see that the corners of the layers just don't really line up - there's a random misalignment, and then a larger repeated bowing effect superimposed - so the corners jiggle around layer-to-layer, but generally move wider out and then come back into line giving the blocks a scalloped edge. Is the pitch of that scalloping 3mm? If so it's probably related to the z-screw somehow - perhaps the axis screw isn't straight, and/or the large nut isn't free to move around in x-y, so the bed gets moved a little bit.

The more random layer-to-layer misalignment might be due to backlash in the belts. Are your short and long belts reasonably tight?

 

[illuminarti 18]

Another thing to try - turn off the fan - how does that effect the print? It might be cooling the nozzle tip too much. And, as George suggested, just try printing hotter, and see how it performs.

 

[edis 0]

Forgot to mention that all parts on my last post were printed at 190°C and 60mm/2 .2mm layer height. I've made another try with different temps and after 210C and then a lot of ozzing appears (i believe that's how it's called) and the color of prints looks more gray than black. My fan isn't cooling nozzle. If i turn it off, the print gets messy.

It's my custom made printer, similar to ultimaker1. My Z stage is made from a ballscrew, not the leadscrew like in UM1.

Part made with 80% flow:

Part made with 90% flow:

Part made with 100% flow:

Part made with 110% flow:

Part made with 120% flow:

Yesterday i've noticed one interesting thing. I was printing these test boxes with a layer height of .2mm. So the Z movement on LCD was like 0.3,0.5,0.7....6.1,6.3,6.5 and then suddenly 6.69,6.89 and then again 7.1mm. (Though in slicer cura 13.11 layer height is set to .2mm).

I'll post pics of my fan and extruder.

 

[gr5 2,167]

You keep talking about "fill" as in "120% fill". Do you mean "flow"? Because Fill doesn't do anything on a part like this that is hollow.

 

190°C and 60mm/2 .2mm

 

That's quite fast. If you are going to print thick .2mm layers and at 190C then you need to slow it down some - try 30mm/sec to see if it helps. That's a lot of cold, thick plastic through a small nozzle. I can achieve that volume at that temperature (barely) with only a little underextrusion but not with just any PLA. Some PLA's are too thick at that temperature. What is your nozzle hole diameter? The Ultimaker normally has .4mm. What kind of printer are you using?

Here is a photo showing the relationship between printing speed, temperature and underextrusion:

http://umforum.ultimaker.com/index.php?/topic/1872-some-calibration-photographs/?p=13194

 

and the color of prints looks more gray than black.

 

What? Is this PLA or ABS?

 

[edis 0]

Yes, sorry, by fill i meant flow. I'm using PLA. I will try reducing the print speed now. But looking at first pictures you can see that the print quality looks quite good, but sometimes the underextrusion happends and i have no clue why..

 

[edis 0]

ok, here's another print, this part printed with such settings:

0.2mm height, 50mm/s speed, 100% flow and 190°C. It looks like underextrusion to me.

Ok, so next i've printed the same part, everything the same except i've dialed the feed rate with controller to 50% so it should be about 25mm/s. Here's the result:

 

Its not very visible in the foto, but i still get the one layer underextruded, though it's a bit less than usual.

 

[illuminarti 18]

Does the bad layer correspond to something inside the print? Like some internal structure starting or stopping?

[peggyb 169]

do you have other filament to try?

sometimes its just the brand/color that is more difficult than another.

 

[edis 0]

Does the bad layer correspond to something inside the print? Like some internal structure starting or stopping?

 

Here's a picture of broken part at the underextruded layer:

I found that i was using different speed for infill, i had infill at 100 mm/s and normal print at 60 mm/s. But after switching filament to white, its a little better i think, o just its not so much visible as on black color.

 

There might be something wrong with my ballscrew..

 

[gr5 2,167]

I think illuminarti's question was because he was wondering if there was a bug in Cura. When you change things on a layer, it can change areas that *should* not have changed. So you didn't really answer his question. Seeing inside doesn't help as we can't see the upper piece. Better to see it in "layer view" in cura.

 

[gr5 2,167]

If you are printing something that you want to look nice - such as artwork - such as yoda, it's best not to have a different speed for the infill. This can cause over extrusion at the speed change when you switch to the "skin".

Also it's best to print slower if you want it to be pretty. Consider 20mm/sec if you aren't in a rush and want it to look very good.

 

[irongland 1]

Just double checking, this is pla right? that white reminds me of some abs I have seen. I don't think it's possible to print abs at the temperatures we are talking about, but some times some one has to ask the dumb questions!

 

[edis 0]

Just double checking, this is pla right? that white reminds me of some abs I have seen. I don't think it's possible to print abs at the temperatures we are talking about, but some times some one has to ask the dumb questions!

 

Yup, it's PLA. I'll look about this into slicer output, if there's any flaws.

Thank you all for your opinions.

 

[edis 0]

Allright, some more interesting update. I was again printing all kind of test parts to find out what's wrong here. So here's how the parts are printed out for me:

 

The height, where underextrusion happens varies with each part. Depending on speed and temp it happens sooner or later.

 

Anyway, the thing that blown my mind this evening was this part. I've got an idea that maybe the retraction is causing this, i'm using quite heavy spring on my feeder:

 

So i turned retraction off, set print speed 60mm/s, temp to 195C. Here's the result, i've canceled print, after notising same things again..:

Then i was pretty frustrated. I went again WITH THE SAME FILE on SD card, just now i've tuned temp to 220C and feed rate to 200%, so it should be like 120mm/s and here's the result:

 

Looks way better and nearly a perfect print. Any ideas why is that? 220C is quite too hot, and previously i had some oozing at this temp, so thats why i'm never using it.

 

[illuminarti 18]

220 is a far better temp for printing PLA at reasonable speeds. For most types of PLA you have to print very very slow at 190º.

Also, in the photo of your extruder - the spring looks too tight to me... it's kind of fanned out, because it's too large for the diameter of screw through it - but if you look at the bottom, where the extruder is actually engaging the spring, it looks like the coils of the spring are touching. You should back off the screw a bit, so the spring still has some room to move when the extruder is loaded. You may be deforming the PLA a bit, and causing intermittent extrusion problems.

 

[gr5 2,167]

At 190C, if I want a good looking print, then I print 20mm/sec (very slow!). I have to print slow when I print this cold. On the other hand I *often* print at 240C. The plastic flows nicely! Like honey instead of toothpaste. And I can print nice and fast e.g. 100mm/sec is easy.

At 190C I can often print at 50mm/sec but I'm afraid to leave it alone and walk away because under-extrusion is SOOO easy at this cold temp. So instead I just slow it down more so I can walk away without being nervous.

 

[edis 0]

At 190C, if I want a good looking print, then I print 20mm/sec (very slow!). I have to print slow when I print this cold. On the other hand I *often* print at 240C. The plastic flows nicely! Like honey instead of toothpaste. And I can print nice and fast e.g. 100mm/sec is easy.

At 190C I can often print at 50mm/sec but I'm afraid to leave it alone and walk away because under-extrusion is SOOO easy at this cold temp. So instead I just slow it down more so I can walk away without being nervous.

 

So by this you mean that if you print e.g. at 190C and 50mm/s you also get underextrusion sometimes? This would mean that everything is normal at my side, just wrong printing settings.

Some time ago i thought, that if you choose wrong settings, you get whole part with bad quality, not just random layers. But what i see in my examples that part looks nice, except some layers, which seems doesn't stick to the previous layer and it looks like underextrusion in the end.

 

[gr5 2,167]

I mean that I can *usually* print on the UM original 190C and 50mm/sec but sometimes it under-extrudes. It's kind of on the edge. It will be minor under-extrusion and the part will be functional but ugly or it will have zero underextrusion and come out quite perfect it's just on the edge.

But if all I care about is functionality then I print at 150mm/sec and 240C.

 

[edis 0]

Thank you for the info. I've tried similar settings to the ones you've mentioned, but nothing helped.

But i think i've indentified a problem. I've printed one part multiple time on multiple speeds and temperatures, and everytime e get bad surface.

Part starts printing, and it's looking good:

This is the start of and end of the first layer.

Then there's the 2nd layer, it's still looking good:

 

But at layer 3, some areas starts looking ugly, infill is looking like good... ugly.. good

Then later on it looks like this;

5th layer:

 

It's being printed at 195C and 40mm/s, tried 210C and 50mm/s or 190C 20mm/s, still the same. Btw, first layer is printed 20mm/s.

 

Tried manually pushing filament though nozzle, it's going pretty easy, feeder motor isn't skipping steps and it also looks quite smooth. Feeder steps per mm are also calibrated.

EVEN if i set flow at 150% i get similar result, nothing really improves or gets worse.

Any ideas?

 

[illuminarti 18]

To me the later layers look a lot like you're just trying to print too cold - you're smearing paste on the print, not laying down smooth beads. Do you have cooling fans kicking on after the first layers? I'd guess they're blowing on the tip of the nozzle and cooling the nozzle so much that the plastic is barely extruding properly.