Jump to content
iccherry

Getting better cylinder walls

Recommended Posts

Posted · Getting better cylinder walls

I am constantly struggling with artifacts in my cylinder walls on my UM3. Blobs, zits, random noise. This seems to always happen in the same places if I use the same model to test with, so it's got to be coming via Cura.

 

I have tweaked retractions, coasting, z-hop, speeds... nothing seems to get nice smooth walls. I've cleaned the extruder. Swapped cores. Cleaned and lubricated every rod, and checked for play. Any ideas? I've tried printing down to 45mm/s at 0.2mm layers, and I feel like I was able to get this quality from much worse printers.

 

Here is an illustration. The rough print was sliced by Cura. It's the best one I was able to get after tweaks. The smooth print was sliced with Prusa Slic3r (and then I hacked in the start and end code from the Cura file to get it to work). The Cura slice is full of irregularities. The other is incredibly smooth. Same STL. Same filament. Same layer heights. I believe there is a 5 degree difference in print temp, but that isn't driving the result (I've tried it). I do understand it's difficult to tell with this filament, but I've done the best I can with the photos to show what I'm talking about.

IMG_20190928_193629~2.jpg

IMG_20190928_193555~2.jpg

IMG_20190928_193608~2.jpg

IMG_20190928_193621~2.jpg

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

I'm very curious to hear what people think about this.  I'm finding the same with Cura 4.2.1 and cylinders.  It would be interesting to compare the g-code the two slicers produce.  Mind posting them?  Probably should post the STL as well.

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

Please use in Cura the Save menu item, not export, to save everything as project, then we have the model and all the settings you use. 

Share this post


Link to post
Share on other sites
Posted (edited) · Getting better cylinder walls

Sure. I'll use an even simpler model, as these are just examples. Here's a 40mm cylinder with 1mm thick walls. That's it. Designed in Fusion 360 with two circles and two extrusions.

 

I used the default 0.40mm "fast" 0.2mm layer height profile with the following two adjustments: 0.80mm line width (because I'm using a 0.8mm nozzle) and I changed the brim to 2mm.

 

Result: hideous.

IMG_20190929_233001.jpg

UM3E_40mm Cylinder.3mf UM3E_40mm Cylinder.gcode

Edited by iccherry

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls
3 hours ago, iccherry said:

0.80mm line width (because I'm using a 0.8mm nozzle)

 

Just an idea, try to set the line width to 0.50 or 0.49 and check the result in the preview.

When you have a wall thickness of 1mm, 0.8 is hard to print because the printer makes a wall with 0.8 and then he has to print a wall with 0.2 which is hard with a 0.8 nozzle.

 

you could also try to set the line width to 1.00 or 0.99, should be no problem.

Share this post


Link to post
Share on other sites
Posted (edited) · Getting better cylinder walls
5 hours ago, Smithy said:

 

Just an idea, try to set the line width to 0.50 or 0.49 and check the result in the preview.

When you have a wall thickness of 1mm, 0.8 is hard to print because the printer makes a wall with 0.8 and then he has to print a wall with 0.2 which is hard with a 0.8 nozzle.

 

you could also try to set the line width to 1.00 or 0.99, should be no problem.

 

Yes, I'd considered that. However, wouldn't that just get rid of the benefit of using a larger nozzle elsewhere in the model? These cylinders are just simple models to show what I'm seeing in more complicated things. I want to be able to print faster (and I'm willing to sacrifice quality in small details), so I'm using a 0.8mm nozzle. Doesn't narrowing the line width defeat that purpose? I'm not sure if Cura does anything dynamically there, do they? I'm reprinting right now with a 0.40mm nozzle to see if that helps. I'll upload results when it's finished.

 

Also, the same nozzle, speeds, temps, retraction, etc in Prusa Slic3r produces this (attached). The walls of both prints are just a hair over 1mm thick. It's clearly a slicing issue, as the stl, filament, and machine are the same between these two. I'm including the hacked together gcode for the Slic3r version, for reference.

IMG_20190930_075658 (2).jpg

40mm Cylinder.gcode

Edited by iccherry

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

Of course it makes little sense to print such thin lines with a 0.8 nozzle, you can also change the wall thickness in the model to .8 or 1.6 and then try the 0.8 nozzle. It is important that after slicing you check in the preview whether only one or two lines are really printed, then the result should also be clean. If the slicer then has to print a very thin line in addition, there could be these problems. If there are not exactly 2 lines (at 1.6 wall thickness) then play with the line width, often a reduction to 0.79 or so already helps.

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls
28 minutes ago, Smithy said:

Of course it makes little sense to print such thin lines with a 0.8 nozzle, you can also change the wall thickness in the model to .8 or 1.6 and then try the 0.8 nozzle. It is important that after slicing you check in the preview whether only one or two lines are really printed, then the result should also be clean. If the slicer then has to print a very thin line in addition, there could be these problems. If there are not exactly 2 lines (at 1.6 wall thickness) then play with the line width, often a reduction to 0.79 or so already helps.

 

Yes, I originally assumed that was the problem also. I have had this problem across many models with various wall thicknesses (almost exclusively using a 0.40mm nozzle). This is an example to show the problem. Honestly, this is just one of the issues I'm seeing (constant extrusion issues seem to be happening, but again, it seems it's Cura, not my machine).

 

Printing with a larger nozzle helps to *show* the problem. It is exaggerating it. It is not causing it. I have just finished printing the same stl with a 0.40mm nozzle and the default 0.35mm line width "fast" profile. So, the wall is approximately 3x the line width. It's harder to see the artifacts this way, especially in a photo on the internet, since the features are half as large, but they are still there. And in person, they aren't difficult to see.

 

Note, the print on the left is the Cura 0.40mm nozzle version. The version on the right is the same one I posted above with 0.80mm nozzle in Prusa Slic3r with the same speeds and temps. Look at the evenness of the lines. The Cura version is quite rough, both inside and outside. There are also some runs in the Cura version layers where there's underextrusion or something.

 

I've been having a lot of problems lately with surface quality, and I'm just trying to figure out how I can do better. I was worried I had a mechanical issue or something, but I figured I'd try a different slicer, just to rule that out, and here is what I'm seeing.

IMG_20190930_090752 (2).jpg

IMG_20190930_090733 (2).jpg

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

Ok, I realize I might be talking to myself here, but I think I'm on to what's actually happening.

 

With the 0.8mm lines, Cura is stuttering the extrusion.  See the green spots? Those are movements with no extrusion.1039161368_Screenshot_2019-09-30gCodeViewer-onlinegcodeviewerandanalyzer(1).thumb.png.430c5a4d1e7c6f2cdc443e441eac0bf2.png

 

Here's the gcode for that section. Note the movements with no E values:

811621490_Screenshot_2019-09-30gCodeViewer-onlinegcodeviewerandanalyzer.thumb.png.5df2e7a70a05fb98cdf9399b074f6ae0.png

 

Now, this introduces fairly visible artifacts in the simulated part. See the vertical lines? Those are the corresponding movements with no extrusion:

471675806_Screenshot_2019-09-30gCodeViewer-onlinegcodeviewerandanalyzer(3).thumb.png.5394db1a2531c5e4c6a2e5139969ea7a.png

 

 

The Slic3r gcode exhibits nothing but the seam, and that's the only place it has movements without extrusion. Here, you can see how clean the simulated extrusion is.782638826_Screenshot_2019-09-30gCodeViewer-onlinegcodeviewerandanalyzer(2).thumb.png.bf9d26ada343dad94288e5928b114351.png

 

 

Finally, I checked the other Cura file that I had sliced with 0.40mm lines. Here's what's odd, Cura starts out doing the middle line by tracing the curve... then it switches to trying to do infill with 45 degree lines. And *then* it tries to go back and fill in the gaps. It makes no sense, when it just needs to plot a circular single fill line, but that's what it's doing.

 

Here, you can see the initial infill is a nice smooth curve. Then it starts to zig zag.

1603166593_Screenshot_2019-09-30gCodeViewer-onlinegcodeviewerandanalyzer(5).thumb.png.529f79bd4bdad77122eed04ec6d4831c.png

 

 

And here's that same section when it come back and tries to cross hatch/fill it.

794979888_Screenshot_2019-09-30gCodeViewer-onlinegcodeviewerandanalyzer(6).thumb.png.0c0826e691576f8d8206022e10b8deb8.png

 

 

Needless to say, the 3d model of that pattern is as ugly as the actual print.

 

So.... I have no idea. Cura seems to just slice curves in odd ways. It's not extruding consistently, and it's also inconsistent with how it's handling the infill.

 

Any thoughts?

 

Screenshot_2019-09-30 gCodeViewer - online gcode viewer and analyzer (2).png

Screenshot_2019-09-30 gCodeViewer - online gcode viewer and analyzer (1).png

Screenshot_2019-09-30 gCodeViewer - online gcode viewer and analyzer .png

Screenshot_2019-09-30 gCodeViewer - online gcode viewer and analyzer (4).png

Screenshot_2019-09-30 gCodeViewer - online gcode viewer and analyzer (3).png

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

Great analysis!

but it is what I said earlier that you have to adjust your line width accordingly with the wall thickness of your object. And I know you have to play with the value and check afterwards the preview until you see a clean line. So for a wall thickness of 1.6 you should set the line width to 0.79 or 0.81 depends on the object.

 

I guess it is a bug, but maybe @burtoogle know more about it.

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

AFAIK it's not necessarily a bug, but just the way small gaps between walls are filled by recent versions of Cura.


If i remember right, "gap filling" can be switched off (one can choose between "everywhere" and "nowhere"). You could try both options and compare the generated gcode.


Another difference is probably the fact that CuraEngine always generates two passes on each outer contour, while other slicers may be generate a single, but slidely thicker line.

 

Share this post


Link to post
Share on other sites
Posted (edited) · Getting better cylinder walls

Thank you for the feedback. I didn't post up the photos (just to keep clutter down, and they don't show anything new), but I actually tried a couple things to address those issues.

 

First, I thought, perhaps it's that gap filling and the middle wall causing the issue. So, I reprinted with 0.40 nozzle and default 0.35 line width (stock profile). Then, I set fill small gaps = nowhere, and set infill to concentric, just in case. Result: still the same. The outer wall extrusion gcode still has skips in it, and the print was still rough. The gcode did looks smoother (it was drawing circles), and it wasn't zigzagging in the middle wall, but that didn't matter.

 

Second, I tested the line thickness. I set the 0.8mm nozzle to 1.0mm line width, which is exactly the width of the wall. Result: still stuttering extrusion. Still an ugly print. Gcode still shows the blips in extrusion. But maybe going over the nozzle size has other problems, so....

 

I have a print going right now with 0.40 nozzle, 0.333 line width, no gap fill, and concentric everything. The gcode still shows the extrusion stuttering, but that should help determine how much line width matters, as it should just require three equal lines to make the 1mm wall.

 

/edit/ It's not quite done, but I can see enough of it to say that the line width didn't make a difference. The finish is still rough, with extrusion irregularity. /edit/

 

/edit2/ I found an issue listing on the Cura github that discusses what appears to be this, but it's unresolved. 

 

https://github.com/Ultimaker/CuraEngine/issues/702

 

They mention the possibility that it's "outer wall wipe distance" or "wall overlap compensation" causing the problem. I have a model printing with those set to zero/off. I'll have to check it out tonight, but it did look (at a quick glance) like the gcode didn't have the extrusion stuttering. The wall wipe didn't seem to have an impact on the code, but the wall overlap did. It's like the calculation for the required extrusion when compensating for the overlap is a little off or perhaps "mathematically correct" but non-constant, leading to surface irregularity. Hopefully that's it! /edit2/

Edited by iccherry

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls

Well. This is just frustrating. Eliminating the outer wall wipe and wall overlap seemed to make an incremental improvement, but there are still extrusion issues. Further, it almost seems like Cura is turning the curve into a rougher polygon than Slic3r. The vertical artifacts from the interpolation of the curve seem much larger in the Cura version.

 

I may just need to open an issue on the Git for this. I am lost for explanations.

 

For reference, on the left is an earlier Cura print. Middle is the Slic3r print. Right is the new Cura print with 0.333 walls, no overlap compensation or wipe. It looks "ok" in the photo, but again, in person, there are a lot of issues. The layers look like some lines are missing in places.

IMG_20191001_211608.thumb.jpg.27504246e8c235e92a1e0224f2f06c82.jpg

 

Share this post


Link to post
Share on other sites
Posted (edited) · Getting better cylinder walls

I've noticed some strange behavior on curves as well.  What version of Cura are you running?

 

Edited by Reywas

Share this post


Link to post
Share on other sites
Posted · Getting better cylinder walls
3 hours ago, Reywas said:

I've noticed some strange behavior on curves as well.  What version of Cura are you running?

 

 Cura 4.3.0 with the most current firmware ( 5.2.11.20190503) on the UM3E.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

Welcome to the Ultimaker Community of 3D printing experts. Visit the following links to read more about our Terms of Use or our Privacy Policy. Thank you!