Zlutz

I'm trying it right now, but looks like it has the same behaviour. Maybe there's an option that needs to be turned on? Can't play with it today anymore so it'll have to wait until next week.

I made a new test file. It's a simple 20mm cube on top of a 30mm cube with 10 0.5mm walls. What you're saying is - it doesn't matter that there's no skin on top because it's not visible? I 100% guarantee that this will will print terrible and it's not going to be functional. Same print with 9 walls works perfectly because it generates skin with 9 walls. It's easy to say "just use 9 walls" when we have a perfect cube geometry, but with uneven geometry you get problems with 5 walls on one side, 3 walls on other side and 6 walls on third side, there is no solution. Expand distance doesn't work because there is no skin generated at all (it does work for my other model and that's fine, I will use it!) I tested older versions of Cura 4.7.0 - same behaviour 3.3.0 - same behaviour 2.5.0 - it behaves like I expect it to behave and it generates skin under walls (screenshot in post above) Cubes for testing.3mf

... I made a quick STL file with just cubes on a cuboid. 46 x 46, 47 x 47 and 48 x 48 cubes on top 200 x 50 cuboid under 5% triangle infill (to make picture clearer). ... so with 3 walls (as on the pictures), only the 46mm cube behaves as I want it to behave, 47 and 48mm cubes are printed DIRECTLY on top of infill, 48mm cube does overlap the walls below, but 47mm cube is "in the air". If I use 2 walls, 46 and 47mm cubes are correctly sliced. If I use 1 wall, all three cubes are correctly sliced If I use 4 or more walls, none of the cubes are correctly sliced Maybe it's the matter of opinions, but I still believe this to be a bug and there should never be brown below green and especially not under red. If I put a 50mm cube on top of a 70mm cube, and make them have 10mm walls, 50mm cube will not touch any walls of the 70mm cube - it will be printed directly on the infill. If I simply reduce the wall count to 9mm, the bottom cube will get 10mm perimeter of "top layers" (1mm because of the size difference, and 9mm to accommodate the 50mm cube, and the walls of the 50mm cube will be printed on the top layers of a 70mm cube. It doesn't make any sense. Edit: I tested older versions of Cura 4.7.0 - same behaviour 3.3.0 - same behaviour 2.5.0 - it behaves like I expect it to behave!

Thanks for the information, so, basically, there's not much I can do about it because my paint drawing explains it; expectation is different from reality... The thing is... the way I drew it will never be a problem, the problem only happens when red on top part starts touching green on the bottom, then yellow underneath becomes brown. I made "new examples" to better illustrate my issue. The thing is, it works exactly as I expect it to work on most of my parts (because it's like on the top picture), I'm not sure if the contours are maybe the problem or it's something else. I will probably print the smaller parts with 100% infill and it will solve the issue, but it's not a viable solution for the larger prints. It will have to be accounted for in the design itself. I still think it's a bug, really - there's no point in having the ability to have 10 outlines, 20 top and bottom layers and then have the slicer put the infill like 0.1mm below the skin at the weakest point of the print...

I did the second file again with 7 walls. It will 100% have less strength than the first try (with 4 walls) as only left and right sides are "properly connected to the layer under", all else is connected almost exclusively to the infill, and outer wall is actually touching the infill at the top. I could probably redo the 3D model where both walls on top would barely touch the walls on the bottom, then I would have only maybe 10mm^2 connection instead of say 40mm^2. CFFFP_holder.3mf I don't know, maybe I'm just paranoid, but the reason I'm investigating this is because I had some of my parts snapped at the connection similar to this (small cuboid on top of the big cylinder without chamfer or fillet). I did 10 top and 10 bottom layers to make the connection stronger, but in this case - I mostly only get infill, and barely one wall under the whole cuboid. Here's the file from the original post, layer 324 is "suspicious". CFFFP_Axle-old.3mf It is invisible on actual print, but red directly on brown doesn't sound right, should be some green or yellow under it... 😄 Here's a drawing of my thoughts (side view of the inside, "standard Cura color scheme"):

Found one more peculiarity on the other file, could be the same thing? Is this not a bug but a feature? Shouldn't there be yellow under every green and red? Slicer is doing the green lines directly on the infill... maybe there's a setting I should turn on/off?

Tested with Cura 5.5.0 and 5.6.0 Printing a smaller pipe on top of the larger pipe creates infill where it shouldn't be when I'm using exactly 6 walls (or 5 walls with alternate extra wall as on attached photos). When I try with up to 5 or 7 and more walls, this doesn't happen. I believe it's an edge case that happens when top pipe is exactly thick enough to (almost) touch the inner wall of the bottom pipe. On attached photos, I'm using a 0.5mm nozzle with 0.6mm wall thickness, and the bug happens when I'm using exactly 6 walls. Presumably, it's because the top pipe is pretty much exactly 8 walls thick, and bottom pipe would be 14 walls thick, 14 - 8 = 6. I made a test to confirm my hypothesis so I tried using 0.5mm wall thickness. In this case, the bug happens when using 7 walls (instead of 6); top pipe is 9 walls in total, bottom pipe would be 16 walls in total, 16 - 9 = 7. I also uploaded the STL file and the profile so you can hopefully reproduce it. The square part should be on the bottom, and the bug is on the layer 324 when using 0.35 layer height, 0.6 width and 6 wall count (or 5 with alternate extra wall). Axle-old.STL 0.6-noretract.curaprofile

Well thank you very much, my bovine friend! This is EXACTLY what I was looking for. I would never think to search for "monotonic" or think it has anything to do with "top/bottom" options... 😄 The funny thing is, this part would take 1:18 to print with and without this option so it doesn't cost anything!

Here it is! 🙂 CFFFP_Test-slicer.3mf

I'm printing a thin thing and it needs to be as smooth as possible while being completely filled up (no holes) I'm using 102% extrusion for that purpose so there's a bit of extra material being "pushed". When the second step goes in the "wrong direction", fresh pushed material meets old pushed material from the first step, and I get too much material at that point Then the third step starts printing and it's perfect at continuation of first step, and looks a bit different at the continuation of the second step... Also, when you look at the final print, you can see a different pattern at step 2 because it's printed in the other direction. I made a quick STL if you want to play with it. It behaves exactly the same. Test-slicer.stl

Slicer works this way: First it prints "1" north-east to south-west Then it doesn't move the print head north for "2", it simply slices it the other way around (south-west to north-east) Then it hast to jump over the printed stuff, and prints the "3" north-east to south-west I would like it to print in the same order (1, 2, 3), but I would like it to print it always north-east to south-west. Is there a setting I can change to make it so? Photo attached - all I want it to do is print "2" in the same direction as "1" and "3"