Getting inner and outer parts of a wall to print consecutively

[LindsayPatten 1]

It seems that by default Cura will print all the inner walls of a part and then all of the outer walls of the part.  If two walls on a part, say the outer perimeter of the part and the inner perimeter of a hole inside the part, are separated by a significant distance on a large size part, this results in long travels between the outer wall segments.  This in turn leads to some filament leaking out during the travel and then the first part of the outer wall not being solid due to the lost leaked filament.  At first glance I thought that if I printed walls inner to outer I wouldn't have this problem but after it finishes the inner walls it goes off to some far away other wall segment to do the inner walls there and then when it does a long travel to come back to do the outer wall on the first segment the first part of that outer wall is messed up due to the lack of filament due to leaking during the lengthy travel.  For small parts you can tune retractions and so forth to minimize this problem, but for large parts it seems to be impossible to completely avoid some leaking during long travels, especially if you need to use somewhat high temperatures in order to maximise interlayer adhesion. 

 

Is there an option that will cause the outer wall of a wall segment to print immediately following the inner wall of that segment?  Or to just not have a special outer wall, with an extra inner wall to take its place?  Or is there some other approach to dealing with this issue?

[GregValiant 1,409]

In the Walls settings do you have "Optimize Wall Printing Order" enabled?

 

This is with it turned on.

Edited May 12 by GregValiant

[LindsayPatten 1]

Thanks for the reply Greg.  I do have Optimise Wall Printing Order checked.  The issue mostly arises with big prints, the wind turbine blade I'm printing at the moment is over 400mm wide, even if the walls are printed in optimal order, the travel distances between wall segments can be long enough to allow a significant amount of filament to be leaked during the travel, and then that filament is "missing" from the early part of the next wall printed.  As long as the outer walls are printed separately from the inner walls the problem is going to occur when there are multiple widely separated walls in the print.

[GregValiant 1,409]

I'm working with 5.7.1.  Looking through the settings there is also "Group Outer Walls" in the "Experimental" section.  

Playing with the two of them it looks like I'm getting the "finish all the walls here before you go over there" behavior you seem to be looking for.  I stretched the model to 700 x 350 and it looked good.

Model geometry also comes into this.  If there are areas where all the inner-walls won't fit (like a necked down area where a hole approaches an outside wall of the model), then there will be travel moves as each of those areas might be treated separately until a full pass around can be made.  (I don't see that in your screenshot though.)

There is a post processor "Retract Continue".  When an extrusion ends and the travel move starts, the script determines the length of all the G0 moves following the extrusion and will continue additional retraction during those travel moves.  That can help to eliminate the oozing that can occur.  I think it would be helpful with larger nozzles.  It does not work with "Z-Hops" enabled as the Cura version is fooled by Z-hop lines in the gcode.

There is also the setting "Extra Prime Amount" that will add more prime than the retracted amount in order to make up the oozed volume.

 

 

[LindsayPatten 1]

Thank you very much Greg!  Unchecking "Group Outer Walls" was exactly what I needed.  Combined with setting wall order to inside to outside and some seam settings the problems I was having have completely disappeared.  I had hoped to print the walls outside to in to produce optimal accuracy but I still get (smaller) issues so I'm going with inside to out which produces almost flawless prints, and the accuracy seems to be good enough for the parts to fit together okay.

 

When I was looking for a solution to this I found a lot of posts from people having the same problem so I think that the addition of this feature will help a lot of people.

[GregValiant 1,409]

"...the addition of this feature will help a lot of people."

If they can figure it out.

So many settings cross-over to affect other settings that it makes it difficult to determine ahead of time what an effect might be.  It's also tough to write descriptions of all those interactions (to many "if's", too many "unless's", and too many "but's").  There will always be some trial and error needed.

Good luck with it.

[LindsayPatten 1]

Thanks again Greg!  Yes, some complication always seems to rear its head.  99% of the print below went very well but in one place, for several layers the slicer had all five layers of the wall, each starting at the trailing edge of the blade, be preceded by a long travel creating an actual hole in the print due to the filament lost to oozing.  In this case all the travels are a result of the area where the wall is thinned by the slot in the wall.

I'm guessing that I will have to "handle this in post processing" but if anyone has any ideas I would love to hear them as I've got a bunch of these to print.

[GregValiant 1,409]

That's ugly.

I zoomed in and it looks like you have a stripe where extrusion stopped (green lines) which I suppose was due to the oozing,  then that poor area starts.  The lump on the end (black circle) might have been some blockage in the nozzle that squirted out leaving a blob.  I'm guessing here.  You might be able to tell more with a magnifying glass.

What material is that?

 

This would be a tough fix in post-process.  It would likely require some hand coding.

I'll assume that the model is proprietary.  If you like you could send me a PM and pass a project file along and I could take look.

Edited May 15 by GregValiant

[LindsayPatten 1]

Thanks for you continuing help Greg.  I've sent you the project file.  Here is a close up picture of the problem area.

There isn't actually a blob there, it is all "missing" extrusion due to material lost to oozing during long travels.  Where the wall narrows where the strut enters the blade, Cura fills the narrowing area with V shaped wall layers with a short single line at the bottom of each V that fills the space to the next larger V.  Unfortunately, it runs around the perimeter of the blade, then travels halfway across the print to add that short little line, then travels halfway across the print back to where it starts the next layer of the wall.  The short little line probably doesn't get printed at all due to the oozing during the first travel, and then the start of the next wall is even worse due to the two long travels.  I guess one could manually edit out the travel and the short line and the next travel.  Shudder.  Ideally, Cura would change the V plus line to continuing one side of the V to fill the area where the short line is and then do the small travel to start the other side of the V.

 

The material is Amazon Basics Silver Silk PLA.  The final print will be in a more durable material, probably PETG.  The bed heater on the Kywoo3D Tycoon IDEX that I'm printing this on isn't working so I'm stuck with PLA for the moment.  The silver silk PLA gives a nice metallic look and the shininess really highlights any printing issues.   I am just doing prototypes at the moment to determine where the mechanical failure points are.

 

There isn't anything really proprietary involved, it's just a personal learning project, I've always been fascinated by wind turbines so I'm having fun building one now that it can be done without needing a lot of equipment or composite fabrication expertise.  The blade is just a standard NACA 0018 profile helical blade.  If I ever produce anything workable I'll post it on thingiverse or someplace.

 

The most common failure mode seems to be for a part to split between two layers so I'm using a higher temperature to get stronger interlayer bonding, which probably contributes the amount of oozing.  It isn't actually retracting during the travels so maybe I need a kick in the head and then figure out how to get it to retract in this circumstance.

 

[LindsayPatten 1]

Just to summarize what I learned on this topic:

 

* The setting Group Outer Walls in the Experimental section, which is enabled by default, when disabled accomplishes what I asked for, i.e. print the outer wall immediately after/before the adjacent inner wall when there are multiple disjoint wall segments.  When in the default enabled state, Cura will print the inner walls of all the wall segments first and then print all the outer walls, hence the "Group Outer Walls" name for the setting.  If you have Wall Ordering to Outer to Inner it will print all the outer wall segments first and then the inner walls by default.

 

* The lack of retraction was probably the actual biggest contributor to my problem, naturally you get a lot less filament lost to oozing with proper retraction.

 

I sent Greg a project file and he made some mods and sent back and, while they don't relate directly to the original question I learned two very useful things:

 

* if you set infill height to twice layer height it only has to print the infill every second layer, which drastically cuts down on print time.  This assumes the infill isn't playing a structural role.

 

* you can use support blockers to easily cut the top off a model, similar to the way you can cut off the bottom by just sinking the bottom of the model below the build plate.

 

My prints no longer have the problem artifacts so I'm pretty pleased.  Thanks again Greg!

 

P.S. One other interesting thing was that after making the setting changes Cura started printing the small fill lines before printing the wall lines, whereas before it would print one wall layer, do a big travel to print one of those small lines, another big travel back to the z seam, etc. so that it was doing two large travels for each one of those small lines:

With four of the little fill lines this eliminates six or seven of the eight large travels.  So, a lot fewer travels and much smaller artifacts from oozing.

 

Edited May 18 by LindsayPatten

[GregValiant 1,409]

I'm pleased you're pleased and that the print shows improvement.

We're supposed to know what we're doing here but so many problems are unique that it can take some head scratching to come up with a solution.

For that model the big clue was looking at the travel moves and seeing that there was no retraction.

 

In regards to infill:

Most prints get their strength from the walls and the infill is just needed to hold up the roof.  When I need internal strength I go with "Grid" at 7% density, Infill Line Multiplier = 3, and change the Infill Line Directions to "[0]", Connect Infill lines enabled.  The print time stretches out, but you get real internal structure rather than a bunch of wimpy lines.