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treyceritops

Printing Inconsistencies. Pleae Help

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Hello all,

I have had my ultimaker for some time now and I have gotten some great prints out of it, but I have also gotten some incredibly terrible inconsistencies in my prints. My latest print was the twisted 6-sided base basic (http://www.thingiverse.com/thing:18672) which started out great, but then it went sour early on. But, after that, later on in the print, it went well again.

The main issue I am asking for help is that with this vase, one side (see pictures below) has some bad printing job, while the other side, 180 degrees around it, has a beautiful print the whole way up. So I do not know what is going on with it or why it is having issues.

Here are my printing settings for Cura 13.06.3:

Layer Height: 0.1

Shell Thickness: 0.4

Retraction Enabled

Bottom/Top Thickness: 0.4

Fill Density: 0

Print Speed: 50

Print Temp: 220 (I generally print at 210 but I read that higher temp might help this. It didn't...)

No support

Diameter: 2.85

Flow: 100

 

Initial Layer Thickness: 0.3

No Cutoff or dual extrusion

Travel Speed: 150

Bottom Layer speed: 20

Infill speed: 0

Minimal layer time: 7

Cooling fan enabled

Overlap: 15

 

Here are the dropbox links for the photos:

https://www.dropbox.com/s/20z6dwnoy49jbcl/2013-06-23%2019.09.28.jpg

https://www.dropbox.com/s/81phe97ok560maj/2013-06-23%2019.09.18.jpg

https://www.dropbox.com/s/n5crcpzejt1toui/2013-06-23%2019.09.08.jpg

https://www.dropbox.com/s/2skr4cp8m8rzid1/2013-06-23%2019.09.00.jpg

Thanks for all of the help.

 

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I suspect that it's a problem in the slicing itself - your settings look sane, and the minimum layer time of 7s should be giving long enough for it to cool between layers. I think that probably the head is backtracking to start the new layer, and its causing problems. This can happen with shapes like this, where the print segments are long, but the corners precess around the shape.

Older versions of Cura had problems with this and would keep trying to move back to the vertex nearest the origin to start the next layer.. that may be what is happening here too. When the head moves back, it drags back over the print, oozing, and making a mess.

Can you post the gcode here as an attachment, or email it to me at gcode@fbrc8.com, and I'll take a look to see what's happening?

 

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I think Illuminatri is probably right but another possibility is that the "good" side is the side facing the fan. If this is true you could try increasing the "Minimal layer time" from 7 seconds to maybe 10 seconds but I have found 5 seconds is usually plenty.

 

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I've often wondered if the 'side facing the fan does better' story is really true? Any part of the print should get pretty much equal instantaneous cooling as it gets extruded, since the fan is right there by the nozzle - although admittedly a bead being extruded while the head is moving in positive X has the least cooling active fan time (since it soon disappears under the fan), while a bead that is printed in negative y direction enjoys the longest potential cooling as the fan remains close and moves along the freshly printed bead as it goes (since most of the fan opening is usually 'behind' the head in the y direction).

But, in terms of position on the bed, the parts of the print on the left (towards the Y axis) typically gets the least cooling overall, since it is most often under/behind the fan opening when the head is printing the parts of the print on the right. And that means it gets pretty much no fan assisted cooling. Whereas the parts of the print on the right are pretty much always getting some fan-assisted air movement over them, even if the fan has moved away somewhat. They're never in the shadow of the fan itself.

Certainly what I have seen regarding warping is that if I'm going to get curling up off the bed, then assuming similar geometry across the bed, I'm most likely to see warping on the right side of the print, since it gets more cooling overall from the fan. (I can get rid of the warping in those circumstances by turning the fan off completely).

I haven't studied it in detail, but I suspect the truth is more complex than 'the side facing the fan prints best'. At the very least I suspect it depends on the direction that the print head is traveling.

Anyone have any thoughts or examples to share?

 

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Thank you for your responses. And I will say that the side that had the pretty printing was actually near the back. The front was the side that had the bad printing. So that is 90 degrees off of the fan cooling idea. Also, illuminarti, I have posted the gcode at this dropbox address: https://www.dropbox.com/s/xb6k19e1or6agj6/Twisted_Vase_Basic.gcode. That should give you the gcode for you to check out.

Another thing that I forgot to mention as I was printing was that the side that had the issues seemed that the plastic was not laying down an equal layer. Everywhere else was laying down a single layer, but it almost laid down a wave of plastic almost like it was underextruding. So a little more and then a little thinner and so on. But it did not carry past the one side that was having problems. And early on in the print and later in the print, it did not have problems at all. It is very peculiar.

Thanks.

 

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The gcode looks fine to me... the print actually starts changing layer at the back of the print, and that gradually curls around to the side nearest x=0 as it follows the shape. I don't see any back tracking or oddities in the path.

I have three thoughts about what might be going on:

1) Positioning error - perhaps you're seeing some backlash or other positioning errors that cause variability in the alignment of the head when printing the mostly-in-the-x-direction lines towards the back of the bed? Does the base of the print show any alignment problems, or gaps between infill and the perimeter? Is there any extra friction when moving the head by hand in the x direction in that part of the bed?

2) Cooling problems - maybe it really is a failure to cool in time, allied to the position of the print relative to the fan. I think its unlikely as your minimum print time should be good enough.

3) Layer change ooze... maybe the layer changes are happening a little slower than they might, due to the combination of x,y and z motion, and the fact that there are some odd defaults and bugs in Marlin that can slow these things down. if there's some oozing that then gets dragged into the next section, that might cause a mess - but as I look at the pictures, I think the messy printing is happening just before the layer change, not after it. So that may not be it either.

I'd check that the mechanics are ok. Maybe try printing a similar sized square, first aligned to the axes, and then at 45 degrees rotation around z, to see how those walls line up. That at least would rule out the effects of the slowly rotating layer start point as a potential source of problems.

 

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Illuminarti,

Those are all great suggestions and I have pictures to show the two prints of the calibraiton cube. I did an open top calibration cube that I scaled to have 40mm x 40mm dimensions. But here is an answer to your questions:

1). The printer does not have any more friction at the center of the build plate where the issue was happening vs. anywhere else. I do have slight gaps in the infill which can be seen in the pictures below.

2). I agree with you that there should be no issue with this.

3). I don't think layer changes (changing colors) have anything to do with the issue. The issue is in the center of the colors. But if you mean the print moving up a layer, that could be an issue. It did seem like the problem was shortly after the print moved up to the next layer. So it moved up, had about 1/2" of decent print, and then it had the bad print area. The layer was changing on the left side of the printer.

Here are the links for the pictures of the cube. The only differences in my printing was that I did 50% infill and a brim at the bottom (which was not necessary). I took pictures from the front, right, back, left, and top, respectively. They are in that order below.

Cube aligned to axes.

Front: https://www.dropbox.com/s/vakk3smon19jfr8/2013-06-25%2021.39.26.jpg

Right: https://www.dropbox.com/s/n9iv2bsog1guv22/2013-06-25%2021.39.39.jpg

Back: https://www.dropbox.com/s/sp7cphx3s2by5z6/2013-06-25%2021.39.48.jpg

Left: https://www.dropbox.com/s/k27flnw7zqq2yo9/2013-06-25%2021.39.57.jpg

Top: https://www.dropbox.com/s/w8l0kjmby2kxdqn/2013-06-25%2021.40.07.jpg

Cube 45 degrees

Front: https://www.dropbox.com/s/blc6s9snqvkln8p/2013-06-26%2016.57.21.jpg

Right: https://www.dropbox.com/s/cjsxdw7117mww4n/2013-06-26%2016.57.27.jpg

Back: https://www.dropbox.com/s/d8va0rzmp3e8a6o/2013-06-26%2016.57.37.jpg

Left: https://www.dropbox.com/s/dy8m0wwkau8hkz3/2013-06-26%2016.57.57.jpg

Top: https://www.dropbox.com/s/yz49r576tzy4v7s/2013-06-26%2020.51.44.jpg

 

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Your issue is a new one for me. I've been reading posts here for a long time and it seems to be something new.

Grasping at straws - some crazy theories:

1) Does the printer pause for a long time (say a second) when it changes layers (i.e. when z screw rotates)? It shouldn't but if it does I have a theory why that would cause this and the fix would be to have it not pause.

What you describe sounds like underextrusion followed by overextrusion. Where the nozzle pressure is building up followed by over extrusion. What could cause that?

2) inconsistent z steps. Does this happen with .2mm steps? If the z movement is inconsistent then a .2mm step should help mask the problem. Also you should put a drop of the green grease that came with you UM on the z screw and run the platform up and down past the grease a few times.

3) Does you z platform stick? Using cura or pronterface, move the Z axis in huge steps - say 100mm vertically. watch carefully to see if it sticks for .1mm and then suddenly moves again. Maybe turn the Z screw by hand. It should be easy to turn with all of the friction being from the stepper motor.

4) Does your Z screw wobble? Is it all the way into the coupler? Look at photos of the z screw coupler on the assembly instructions and compare to your coupler visually.

 

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