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Nicolinux

Top Layers not touching - UM2

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ok i think i found another resistance

when i made the roberts V2 feeder i cutted a piece of the bowden as usual but i forgot to drill a transition in to the cutted bowden were it enters the feeder and when i try to put in filament by hand it has a lot resistance..

i will improve that next monday and post the results. i have a feeling that then i will be able to run normal prints and extrusion test up to 15mm3/s like on my older UM2

 

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The edges look overextruded and the center underextruded which is what you would expect if printing somewhat fast because the bowden stores pressure on the filament like a spring and as you slow down for the edges it overextrudes and then when you speed up towards the middle it underextrudes.

 

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I loosened the four screws too and printed a test cube. Look at the pattern. Looks as if it is inverted diagonally.

 

It's odd that there seems to be such a sharp transition at the bottom-left to top right diagonal.

Does changing your acceleration speed (Maintenance -> Advanced -> Motion Settings) make a difference to how the pattern comes out?

 

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@3DMaker4U: Yes. Lower half first, then upper half.

@gr5: This particular cube was printed somewhat fast, but most of the other ones where printed around 30-40 mm/s. Here are the print settings:

 

  • layer height: 0.15
  • shell: 0.8
  • bottom/top: 0.8
  • speed: 45
  • temp: 210

 

@Illuminarti: The first cube was printed with an acceleration of 1500 (is this the default? I can't remember).

Then I printed the same cube with the same acceleration but at 0.1 layer height:

C2

And then another at 0.1 layer height but with accleration set to 700:

C3

 

The pattern changes but other than that, the gaps are still there.

 

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I'd like to add another remark. We are printing quite a lot of test cubes here and talk shop about print settings and theoretical speed/volume constraints.

M1

M2

But as you can see, this issue is real. It does happen with real prints and it is bothersome. It's not just that some of us are to dumb to choose print settings.

This particular object (bathroom sign) was printed at 0.24 layer height, 50 mm/s speed and 210° temperature. The filament volume that goes through the nozzle (or at least that's pushed by the feeder) is 4.8 mm^3/s which an UM2 should handle well.

 

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210*C is way too low IMO.

Since we have no real solution for this issue, we have to print much much hotter. As I said before only 240-245C and 105-110% flow rate works for us (on both UM2 here, with Ultimaker PLA filament).

If you're printing with high temps then you have to clean the nozzle (atomic) very often, for us that's 2-3 times a week or every time before we change the colour.

 

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Well, 210 is not too low if the printer would work properly in this regard. Printing that hot is just a hotfix (see what I did here :p ) and should not be a permanent solution. Printing at high temperatures has its problems and should be avoided when not necessary.

 

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For us that's the business not a hobby, we need good quality prints no matter what.

We've tried so many things so far with no luck, new nozzle (even two), new teflon insulator, new fans and who knows what else.

Both our UM2's are is great condition and always well maintained.

You can print 210-220C, that's your choice, but won't be surprised if you see all those gaps on the top.

You are right, printer should work at 210C but UM2 is not, what can we do ?

 

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I would expect lower accelerations to give worse qualtiy. I beleive default XY acceleration is 5000 mm/sec/sec (not 1500). 5000 is what my UM2 is now and I don't think I've ever changed it (currently my UMO is at 4000).

The reason is it's really bad for the feeder to ever change speeds. The more it changes speeds the worse the quality. If you have high jerk (default is 20mm/sec) and high acceleration (5000 mm/sec/sec) then the feeder doesn't slow down much and not for very long.

You want the extruder to extrude at a constant rate - never speeding up or slowing down or doing so minimally.

Everytime you ask it to speed up it will underextrude briefly and vice versa.

One fix is to just print slow - if you print at 20mm/sec it will never slow down because the jerk setting allows it to make a sharp corner without slowing down. 35mm/sec is *almost* as good quality and so on.

So I have 2 recommendations:

1) Keep acceleration high - 5000mm/sec (note that this can cause ringing along the walls on sharp corners however).

2) For this particular print, I recommend printing the bottom and top layers slower (say 30mm/sec) and then printing much faster (possibly 75mm/sec) on all the other layers. You can do this with a plugin. Changing speed on a layer change should be safe because it should print the interior lines first and by the time it gets to the final outer shell it should be at a constant feeder rate speed and everything equalized.

 

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Hi i have the same problem .

 

DSCF4846aDSCF4849

 

i use ultimaker2 for architectural modell. walls are ok more or less, but the horizontal flat surfaces are bad.

 

everythings was ok till cura update 14.03 since then the problem is exists. last week i installed the firmware for 14,03 again and the next printing was good, and nothing more.

 

for me it is job not only for fun

 

András

 

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Hi András,

Just saw your photos. I am following this thread for a while because it happens every so often for me too. I also make architectural prints from time to time, and this looks so much familiar - bad top layers and walls shells not touching.

So far, the counter-measure for this is cleaning the nozzle and printing slower. It looks like the temperature you're using is already hot enough. Another suggestion is to use more top layers - the mesh looks very thin as it was not enough layers to build a solid looking surface. I may be wrong, of course, this is only my impression. What are your printing parameters?

BTW, with Cura and the firmware 14.07 it is possible to get decent-looking prints, you can safely upgrade to this version.

 

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Oh - I should mention that that print of the "people" looks underextruded. Maybe go to 220C or slow it down a little more. Different colors need different temps.

 

Since I don't have anything in the printing queue now, I just printed the same object with default acceleration and jerk settings and temperature of 235°.

Do you believe me now that there is a real issue here?

B2

B1

 

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This is getting a little crazy because there might be 3 distinct issues going through this thread:

1) Underextruded top layers (the main thread!)

2) Underextrsusion everywhere (the main problem?)

3) Overextruded edges

@nicolinux - regarding #3, your orange "people" photo just above this post looks like #3 is fixed with faster acceleration. The edges look better than the cube you printed earlier where the edges were overextruded. You still clearly have underextrsuion - on the top layer if nowhere else. I don't know what the cause is but another solution might be to just increase the flow by about 25%

Do you have the latest firmware installed? I don't. Maybe that's why I don't have a problem? The latest firmware changed PID stuff for both nozzle and bed.

 

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i use ultimaker2 for architectural modell. walls are ok more or less, but the horizontal flat surfaces are bad.

 

everythings was ok till cura update 14.03 since then the problem is exists. last week i installed the firmware for 14,03 again and the next printing was good, and nothing more.

 

for me it is job not only for fun

 

András

 

@varsanny - Did you also use different slicers? The only changes I can think of in the firmware is that the PID control for both nozzle and bed changed. This affects temperature. You might want to observe the nozzle temperature in the TUNE menu while you are printing to see if it is stable or if it fluctuates.

Or just stick with firmware 14.03 for now (I haven't upgraded firmware in maybe 6 months as I'm pretty happy with the current firmware) until someone figures out the problem and Daid fixes it.

 

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here is another photo of a house model

DSCF5147

 

the problem is the same: all flat surface is full of gaps only the first layer is ok .

settings are:

layer height:0,2

shell thickness 0,8

bottom/ top thickness: 0,6

fill density: 23

print speed 55

nozzle size :0.4

temp : 210 or 230 ( it was 2 weeks ago, nowdays i set temp 230-235 manually

(the temp is stable during printing,)

can the changing of the nozzle( or anything else ) help?

 

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Hi varsanyy,

Can't see the images in your album, so some theoretical suggestions based on my empirical experience:

 

  1. Perform atomic cleaning of the printhead
  2. Increase top thickness to 0.8 or even all the way to 1.2 mm
  3. Reduce the print speed to 30 or 40 mm/s

The rest of the parameters seem to be OK. What type of the filament do you use? My "Architects Stone" by Faberdashery needs 240C, for example.

 

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