Retraction issue at layer change

[Refleks 0]

A lot of my cylindrical objects are having this issue (not my picture but similar) and on a facebook group someone posted the following regarding it:

 

Quote

This is, in fact, from retraction. Specifically, the retraction that happens either during the change between perimeters, or during the change from infill perimeters, or between layers. Any one of them could be the culprit.
What's happening is that--even though you're retracting--a small amount of filament is still oozing out before the retraction completes, and therefore it takes a second or two for the hotend to build pressure up again before extruding normally.
My suggestions are:
1. Turn your nozzle temp down. 5° may be able to cure it.
2. Increase your retraction *speed*, to reduce the amount of time available for ooze.
3. Introduce some extra restart distance. There should be a setting in whatever slicer you use that will allow you to prime the nozzle ever so slightly after every retract, in order to compensate for the ooze.

Was looking to confirm the issue is retraction and not something else, and for some advice regarding best practices to minimize this characteristic. I generally print at .2 or .1 layer heights, and the adhesion seems weaker at anything larger (to the point where the layers just crumble).  This is with multiple PLA brands and colors.  In general the print looks outstanding otherwise.


Regards
 

[burtoogle 442]

I would recommend setting the max comb distance without retract setting to something like 10-20 (mm) which will stop the major dribble that occurs when combing. It's likely that's what's causing the crappy wall downstream of the z-seam you can see in your photo.

[Guest]

Just thinking about what I see when I watch Cura generated gcode being executed by my machines, but... Why would Cura be creating gcode with a distance longer than 10-20mm on that object for the outer wall, assuming the outer wall is done last which is the default?  FYI - I don't use single extrusion walls and I don't think this object did either (I use 3 layers) and Cura does them from inner-to-outer by default and there's just one nozzle-distance of travel between each wall.

 

I also implemented a plugin-script, that someone else originally wrote a proper-plugin for [thanks for the idea, whoever you are], to solve dribble problems, but the Cura developers didn't "accept" it [I.E. implement it as a standard option].. but I don't think it solves this problem (because I'm not sure it's a combing problem).

 

I personally decrease speed on outer walls to <= 40mm/s.  It hardly increases total print time, but it has solved a number of issues for me from bumps on the surface [with Marlin], to what I call "feathering" [with Sailfish] where it's really quite a thin extrusion that you can partially see through.

 

Having said that, one rounded object I printed recently still has the zipper present, which looks a lot like that photo above, except there's only one bump on each layer - where that photo seems to have quite a few bumps on each.  Looks like what was getting with Marlin before I converted all my machines to Sailfish.  I live with the one bump though, I can't see a way to get rid of it.

 

Just my 2 cents.  Maybe it is combing from the other side of the object for some reason, it wouldn't surprise me.

[Guest]

To be clearer on my thoughts, which may be wrong, and please let me know, this to me is like a machine's acceleration algorithm vs the physical extruder's ability via the firmware's creator's guessed default extruder advance setting's ability to keep-up consistently issue.  (Mouthful?)  Bowden/Direct-drive has never been a Boolean setting in firmware's so they can't possibly guess correctly [my machine type] or let me know what they expected for what the default/tested-settings originally were [in terms of acceleration & speed I'm running at].  Lowering the speed simply makes it work better.  Which is why I believe I see different, stark, quality output differences in different firmware's with some faster print settings, that I no longer use, in visible areas.  Probably, no firmware has been refined with my particular settings for the machine's physical attributes that I've personally built/or converted over to that firmware, so that leaves just this one option to reduce the acceleration vs extruder output issue(s) I can see, which I do via the maximum speed.

 

Acceleration, here, being the area in the picture where the problem is occurring.  It's a crappy science.  But I have tested quite a few gcode changes for a fix [and yet failed] for dealing with artefacts like what's in that picture above, at the speed the machine's I build can run at.

[Guest]

I should add, the gcode concerning actual extrusion of material (E values, as generated by Cura) shouldn't have to deal with any of this, if the problem doesn't exist when a slower speed is selected for the visible outlines.  I.E. not a slicer problem, only a firmware problem.