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Brilliant_Name

Zits on curved surfaces, crazy toolpath

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Hi!

Using Cura 3.6 with an Ender 3, calibrated extruder, flow and retraction. My filament diameter is consistent.

I have issues with zits on the walls. The effect is at it's worst with thin walls.

The results are very repeatable, the zits are always in the same places. 

From what I was able to deduct,  it is related to Cura toolpath generation, jumping all over the place.

 

First example is a simple cookie cutter, double thickness walls. The part on top is just a cutout of the same model, printed with the same setting. Much better, but without the interior, there was a lot less jumping around. Not even close to good.

 

Decided to try Slic3r, and lo and behold, day and night difference.

I've made a test model, just an double walled oval and some pins. 

Bottom is Cura.

 

I tried coasting, different z seam settings, nothing worked.

 

So, before I give up on Cura, any ideas?

 

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Over-retraction is a common source of zits because it sucks air into the nozzle. You're using 5.5 mm which does seem rather a lot for a short bowden. I run a bowden printer and only use 4.5mm and get very good retractions. Also, I would have thought that coasting is going to make it worse.

The inner wall speed in your profile is very high. For good quality, I tend to use the same speed (and line width) for inner and outer walls so that the extruder pressure doesn't need to change. This can help reduce the bump at the z-seam.

 

It's generally worth enabling the wall print order optimization.

 

Hope this helps.

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Just now, smartavionics said:

Over-retraction is a common source of zits because it sucks air into the nozzle. You're using 5.5 mm which does seem rather a lot for a short bowden. I run a bowden printer and only use 4.5mm and get very good retractions. Also, I would have thought that coasting is going to make it worse.

The inner wall speed in your profile is very high. For good quality, I tend to use the same speed (and line width) for inner and outer walls so that the extruder pressure doesn't need to change. This can help reduce the bump at the z-seam.

 

It's generally worth enabling the wall print order optimization.

 

Hope this helps.

 

With regards to retraction, I can get by with 3.5 mm but I have upped it after adding Retraction extra prime to fix the underextrusion on layer start/after long travels.

In my testing coasting didn't affect prints so I left it on.

 

I'll see if the inner wall speed changes things.

 

The photos attached show the same model printed with the same settings. The upper one I just cut in Meshmixer. The difference is staggering. I'm guessing the lack of inner model made for much less travel and a better toolpath.

20181120_204001.jpg

20181120_203827.jpg

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Tried Simplify3D, and the differences are evident. I've been using Cura for a month, tweaking and tuning, I got this result after a couple of hours with S3D.

I still have to properly tune it, but at least it's not generating garbage like Cura.

I do like the Cura interface more and would like to use it, but with results like these it's just pointless.

 

If someone has ideas, please chime in.

Cura is the bottom one.

 

 

 

20181121_183833.thumb.jpg.92b5f95377891510b735885a6a0d1d3d.jpg20181121_183944.thumb.jpg.37d0f97f1d7743029065370632fe328c.jpg20181121_165751.thumb.jpg.dd9388cfd1049719724ea8c8de537f66.jpg20181121_165717.thumb.jpg.6e202d5b50b26f8d5c5a74321e8d558d.jpg

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A bunch of Cura prints.

The zits are always in the same place, even though I changed a lot of settings. So it's not a random mechanical slop or filament issue.

Other slicers don't exhibit any of the artifacts.

 

Settings changed, from top to bottom:

18. combing off

16. reset to draft, extra prime amount to 0.4

13. z seam alignment to sharpest

12. z seam alignment to shortest

 

Any input would be very welcome.

20181121_190137.thumb.jpg.34984eb115a684aa11589c80c10d5c71.jpgI

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2 hours ago, smartavionics said:

Set the z-seam to user defined and specify a non-zero value for at least one of x or y to force the seam to be in one place. If the zits pattern changes then you know that the problem is likely to be related to layer change/retraction.

 

Thanks for the tip. I either forgot to test or missed the option. 

The results are good, zits on the sides of the oval are mostly gone, but others are still present and even in the same places.

 

I've also attached the Cura travels, for both Z seam settings and I'm even more confused. They are not that different and nothing weird on the sides of the oval that would explain the difference in prints.

 

 

Top: Simplify3D

Middle: Cura Z seam alignment set to user defined

Bottom: Cura Z seam alihnment set to shortest

20181121_231952.thumb.jpg.4505e63ce3dc590db8428ae53861ac44.jpg

20181121_232140.thumb.jpg.1df7e95fd6912c9ce83b8b105da069f2.jpg

20181121_232026.jpg

cura-z-seam-alignment-travels.jpg

cura-z-seam-alignment-travels-shortest.jpg

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Sorry, I don't have any ideas but let's think about this. If you are not over-retracting and sucking in air then it must be something that is causing the extrusion rate to change. Looking at the gcode there's nothing obvious that's doing that.

 

If you take away the pins and just have the round object do you still get any zits?

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2 minutes ago, smartavionics said:

Sorry, I don't have any ideas but let's think about this. If you are not over-retracting and sucking in air then it must be something that is causing the extrusion rate to change. Looking at the gcode there's nothing obvious that's doing that.

 

If you take away the pins and just have the round object do you still get any zits?

 

I lowered my retraction to 3.5mm from the 5mm, no change. 3.5mm is the minimum for my bowden setup.

 

I'll try the oval again after my current print is done.

I'm printing another cookie cutter and with user defined z seam it's coming out much better, but still, the zits show.

 

 

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50 minutes ago, smartavionics said:

If you take away the pins and just have the round object do you still get any zits?

 

Just printed the oval without the pins and I still get zits, though less of them.

Printed two of them, back to back to confirm that they would be in the same place, and sure enough, same places.

 

 

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Having objects inside makes it much worse. Here's the cookie cutter, with z-seam alignment set to user.

I've also attached the 3mf file.

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CE3_cc-poop-emoji.3mf

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In the mean time I changed my firmware to Klipper, but the issue persist and more artifacts.

I also noticed that the Cura print will slow down in on outer walls producing the vertical lines.

 

The Cura gcode is also 50% larger.

 

S3D on the right, Cura on the left. S3d print was also 40% faster.

20181125_164300.thumb.jpg.3f32192e17d69b3fbc82ff8eae2c6aa6.jpg20181125_164409.thumb.jpg.6894685b41361b9bdcec9d7b57624a37.jpg

 

 

Cura on the bottom, S3D top.

20181125_164127.thumb.jpg.74b5ce07d7170a75d04a5eb76cc0f1ae.jpg

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