SOLVED Stuttering extrusion at the start of each new layer

[kulfuerst 6]

3 hours ago, samtaylor said:

Retraction prime extra amount. Is the answer your all looking for. 

 

Unfortunately, no. It's not that simple.

Retraction extra prime compensates for material that oozes away during travel moves, but this is not the issue here. A function that would solve the above mentioned problem (but doesn't exist), would be something like "gap-fill extra prime amount" that compensates for material that oozes away during low flowrate print moves.

 

[Camaro 0]

9 hours ago, samtaylor said:

Retraction prime extra amount. Is the answer your all looking for. 

As kulfuerst mentioned, Extra Prime didn't solve this issue, but also led to blobs on other parts of the print.
I dried my filament and played with 'Equalize Filament Flow' but wasn't able to improve the issue. I will probably revisit this setting though later on.
As I had this problem with any slicer and a freind  of mine has a similar setup I thought about what about my hardware is different from his: than it occured to me, that I'm running an 8-bit board with a 0.9° extruder motor on the E3D Titan and use 1/16 micro stepping on my extruder which led to about 800 steps per mm. I changed to 1/8 microstepping  which massively improved quality. I guess the necessary step rate for driving the extruder on the retracts simply exceeded the one my board was possible to generate.
I'm not a 100% sure about this explaination, but reducing the microstepps worked for me. This also wouldn't explain why this problem didn't appear after each retract.
As a next step I want to exchange this board with an 32-bit one. After that I will try increasing the microstepps again and if I'm right the problem shouldn't reoccur.

Edited April 10, 2019 by Camaro

[ungutknut 4]

On 11/24/2018 at 9:40 PM, Smithy said:

And is it spread among different printer types or can it be narrowed to a specific type? 

 

I never had such an issue, that's why I am asking for.

Just a quick update to my findings on this issue:

 

I think I got it fixed now and what made the biggest difference was to set a small value (e.g. 1mm) for "max comb distance with no retract". These unretracted travel moves over printed parts were the cause for filament oozing away before each layer.

 

A suggestion to people experimenting with "equalize filament flow" and such: there's a new feature in marlin called "linear advance"... looks very promising although I haven't yet used it.

[Camaro 0]

Hi,
yes 'max comb distance' brought some improvement for me too. Even better worked enabling 'connect infill lines' and turning off combing completely. (this is similar to what slic3r does by default) This results in slightly more filament used, but improved my print quality a lot.
I also experimented with the Linear Advance feature in Marlin. My bowden tube is about 60cm in length, which resulted in a huge K-factor for the algorithm. This in turn slowed my printing speed down a lot (probably due to other not optimal settings made in Marlin) and made the extruder quite noisy. At those speeds the quality was acceptable even without LA and at least the extruder was quiet.
I also tried the Pressure Advance feature in Klipper, which also caused the extruder to be noisy, and mainly fixed the overextruded edges. So I turned it off again until I could fix the main issue.
Hope this helps someone with similar quality issues.
 

Edited April 11, 2019 by Camaro

[gr5 2,234]

The reason these topics are fragmented and rare I think is because most people (like me) don't experience them.

 

It's hard to diagnose a problem when it doesn't happen to me even when printing at 150mm/sec.

 

 

[Camaro 0]

Yes, I would say so too. but that makes it really hard to find a solution for it. I also would guess that this is some kind of configuration issue, as I already swapped out every possible component, but nothing really worked.

The last thing I changed were the Stepper drivers. I previously had TMC2130 on XYZ and MKS LV8729 for my Extruder. Now I use TMC5160 for all axis. They are total overkill but at least it reduced the issue further. However, this couldn't have been an issue on its own, because a friend of mine used the same combination and had no problem at all.
I am on high-end hardware for the whole extrusion system now but still have the problem on higher speeds.

 

@gr5 Are you printing with a direct extruder? But with 150mm/s printing speed, I guess it's a bowden. And if so, how long is your bowden tube?

I will report back if I have done further testing on this issue. Until then I'm printing slow (<65mm/s), which is kind of a shame for a CoreXY..

[kulfuerst 6]

Okay this is going to be my last post on this topic since the issue has been fixed a while ago. The fix is posted on page 1 of this thread. I have answered numerous personal messages on other platforms where I also posted this question and the fix has so far been 100% successful with everyone who came to me directly as well as myself. People have also shared before and after pictures with me like the one I'm attaching here.

@gr5
Printing at 150mm/s makes the issue far less likely to appear, as anything that increases the feedrate of the extruder (layer thickness, layer height, print speed, flow...) masks the issue.

[kulfuerst 6]

 

Solved the issue for another person. Before - After

[MrBackup 0]

 

Hello @kulfuerst, I don't speak English so I'm using Google Translate, so excuse my language. I believe I'm experiencing the same underextrusion problem after the z seam, I've already tried several configurations without success. I read your post but it wasn't clear which setting I should actually change. can you help me please?

 

 

 

the rest of the print is very good in my opinion, the problem is really this underextrusion after the z seam

 

 

 

Edited August 26 by MrBackup

[gr5 2,234]

I see many horizontal lines even in the "good" areas of the print.  This is usually caused when your vertical axis is inconsistent: some layers it moves the proper amount (e.g. .2mm) and some layers it moves a little less and some layers it moves a little more.

 

On the layers where it moves less, the layer sticks out.  You can feel the bump.  on layers where it moves more, the layer sticks inwards or even has severe underextrusion.  That's what I suspect is happening. 

 

A good test is to see if this is all Z related or not is to check if the entire layer is underextruded or overextruded.  Or if the problem recovers part way around.  Not the best test as it's possible the Z axis slowly recovered but usually the entire layer will stick out or be underextruded.  So I'd check that first by looking at the part carefully all the way around.

 

Also sometimes cura just skips printing a layer entirely due to issues with the model.  I'd look carefully at every layer in cure PREPARE view and make sure there aren't any missing layers.

 

There are many other possible causes of underextrusion - for example filament tangle at the spool.

 

If the problem is inconsistent Z movement, one fix is often to clean all the dirt from the Z screws.

 

[MrBackup 0]

Regarding the z axis, I even bought those "oldham couplings" to make the change (they haven't arrived yet). The strange thing is that the problem only happens after the seams, and in some pieces this problem doesn't even appear.

 

The horizontal lines in the photos look more marked than they really are, but they are still there, I don't doubt that the cause of this underextrusion is the z-axis. I'm waiting for the new couplings to test

 

I'm going to test printing very slowly (30mm/s) to see if this possibly compensates for the unregulated z axis. until these new couplings arrive, maybe right? 
I will update here

 

thanks for now @gr5

 

 

Edited August 26 by MrBackup

[gr5 2,234]

well the above prints look fine regarding z axis.  So back to the first print.  I don't know what the problem is.  Filament tangle?

 

Happening at layer change is not surprising as there are more stresses there in that there is a pause while it changes and filament can leak out during the (very brief) pause and then it can underextrude.

 

Also make sure "retract at layer change" is disabled.

[MrBackup 0]

@gr5 I managed to solve it! By reducing the hot end temperature from 205°c to 190°c the sub extrusion practically disappeared. After that, just a few small adjustments to the speed of the outer wall to print slower and problem solved! thank you very much