Did you download and try the burtoogle version?  That will solve all your problems.  I feel like I'm talking but you're not listening.  Sorry - it's a little frustrating when I get the same question 10 times and 9 people try my answer and are like "that's amazing" and then the tenth person seems to ignore me.

I'm wanting to print a hollow hexagonal tube in which the wall thickness in the model is 0.4 mm, the same as my nozzle. (Screenshot (40).png)

The additional 0.4 mm is my nozzle width.  So what Cura does, is it places the center of the line exactly at the wall perimeter of the geometry.  So each exterior wall is going to be exactly 0.2 mm (or half the nozzle diameter) beyond the geometry of the model.  So when it is, say, a tube, with 0.4 mm wall thickness, Cura is stumped.  And when I put that on surface mode, it tries to trace both the outer wall and inner wall, thus drawing two walls instead of one.

gr5, Torgeir; Thanks for your comments and help. I have downloaded the Arachne Engine Beta and voila!  It does print single walls on my part. Wow that is amazing. I have to adjust a few things but overall it does what I wanted it to do. I can now print models that has internal features as well as perfect thin walls.

Thanks, geert_2.  But the issue is visible in the slicer.  As for the version gr5 was referring to, i believe it was the burtoogle version.  I agree that it draws strokes inside of the edge, not on it.  But the standard Cura does trace the actual model edge and it shows that in the preview.  I measure the cube away from the corners and bottom layers because of the effects you mentioned.

Cause there is two walls, the slicer try the closest path and this is why the surface is uneven esp. at the top because  the wall distance increase at this place.

I printed a 25 mm³ cube and found that my printer is spot on.  But in the X and Y axis, that 25 mm prints at exactly 25.4 mm.

There is a good reason that cura has never been able to do this but I don't want to get into it unless you really want to know.  Just trust me that it's a pretty good reason.  But what you ask for has been asked by so many thousands (millions?) of people.  And now I believe (I'm not certain) that Arachne can do this. Maybe.

4) So what you see in the third diagram you show?  That's fixed in the burtoogle version of cura.  The official cura release doesn't do thin walls great.  Burtoogle version has some nice fixes for thin walls.

4) So what you see in the third diagram you show?  That's fixed in the burtoogle version of cura.  The official cura release doesn't do thin walls great.  Burtoogle version has some nice fixes for thin walls.

Now if your cube is hollow it also steps inward (into the wall) for the inner walls. So if you have a hollow cube with 3mm thick walls, cura knows to attempt to print them thinner than that.

When I check the "Print thin walls" option, it does fill in those gaps but instead of the nozzle tracing direct paths between the vertices, it scribbles several of the lines, where the gaps would otherwise be.  (Screenshot (42).png and Screenshot (43).png)

I did download and try the burtoogle version.  It works great if the tube is square, but was no different on the hexagonal tube.  Thanks.  I might upload an stl, but to be honest, I decided I liked the double-thick wall that was produced.  As it turns out, a 0.8mm thick hex tube that is 1/4" minus 0.4mm across flats is incredibly strong in PLA at 190°C.

Now if your cube is hollow it also steps inward (into the wall) for the inner walls. So if you have a hollow cube with 3mm thick walls, cura knows to attempt to print them thinner than that.

ISCAR

gr5, thanks!  Sorry I failed to respond to your suggestion.  I'm told to stay home from work so, being with my family which I love, I'm way busier than normal. LOL.  6 home-school kids and an exhausted wife.  I'm not ignoring you.

I have tried to print single wall with CURA for a while now. I have managed to get some results but using the surface mode and designing parts using Fusion 360 surface mode as I have failed to get CURA to print my 0.4 mm walls with a single pass.

When making small text, I make the legs 0.5mm wide instead of 0.4mm, to avoid gaps when the STL might make the walls just a little bit thinner than 0.4mm in corners (and cause gaps), due to the triangles. But I am using an older Cura version, so I don't know how the newer versions handle this.

5) What you show in the first photo - Cura can't do that - the way it thinks about inside and outside - it just can't do that.  Sorry.  People (including me) have been asking for that for about 6 years now.  Programmers say it's not going to happen.  Some day it will happen but don't hold your breath.  Actually there is a mode called "vase mode" that can do what you show in the first photo - but the way you do that is a hack.  You first give cura A *solid* model with the inside filled in solid.  Than choose vase mode and it will just do one pass around the outer wall just like you want.  You have to set the line width to how thick you want the walls and even if you have a 0.4mm nozzle you can do 0.8mm walls if that's what you tell cura to do but cura will do it in one pass.

You probably want to download the burtoogle version - I suspect it will do a somewhat better job or burtoogle might have suggestions but he's probably asleep right now - maybe in a few more hours he can answer you.

Using the default setting for my printer (UM2E+) and used fine profile (0.1 mm line height) and changed "Line width" to 0.5 mm. Checked the "Saved" gcode file in Cura Arachne Beta and found no issues, then opened the same file in S3D and the object was superb. (This is the best "water test" I can do to be reasonably sure that this print will "shine".)

SFM to RPM

gr5, Torgeir; Thanks for your comments and help. I have downloaded the Arachne Engine Beta and voila!  It does print single walls on my part. Wow that is amazing. I have to adjust a few things but overall it does what I wanted it to do. I can now print models that has internal features as well as perfect thin walls.

Maybe in the future there might be an "engineering mode" ?  Slicing might take longer due to the extra calculations but I'd use it in a heart beat.

1) I'm not sure if you know what 25 cubic mm means.  It's a volume.  If it is a perfect cube then it would be 2.9mm on a side.  Is that what you were trying to say?  I'm not sure what you mean.

Did you download and try the burtoogle version?  That will solve all your problems.  I feel like I'm talking but you're not listening.  Sorry - it's a little frustrating when I get the same question 10 times and 9 people try my answer and are like "that's amazing" and then the tenth person seems to ignore me.

Maybe in the future there might be an "engineering mode" ?  Slicing might take longer due to the extra calculations but I'd use it in a heart beat.

The messy scribbles are...acceptable, but I'd really like a cleaner, faster print.  I would just make a solid model and use the "vase" or "Surface" mode, but I really need those holes in the sides.

Right - you could set the line width to 0.39 or 0.35 - you can print down to about 0.35 without much (any?) noticable loss in quality.  Or up to around 0.6 (but you may need to print slower).

I think the extra width that you measure might come from ringing- and thickening-effects around corners? When slowing down to take a corner, the nozzle inside pressure does not immediately drop, it lags, so the nozzle extrudes a bit too much compared to the now slower speed. This makes corners thicker. Analog for ringing, sine-wave mechanical oscillations around corners. This could easily explain 0.2mm extra width. Also blobs and overextrusion could explain that, if they would be present. Also, "elephant feet", the sagging of the first layers, could make a model seem wider than it is, if you measure it.

You may also try printing model aircraft wing parts with "added" profile settings. Some sellers give parts of model for free to test how their products looks after printing.

I think the extra width that you measure might come from ringing- and thickening-effects around corners? When slowing down to take a corner, the nozzle inside pressure does not immediately drop, it lags, so the nozzle extrudes a bit too much compared to the now slower speed. This makes corners thicker. Analog for ringing, sine-wave mechanical oscillations around corners. This could easily explain 0.2mm extra width. Also blobs and overextrusion could explain that, if they would be present. Also, "elephant feet", the sagging of the first layers, could make a model seem wider than it is, if you measure it.

I have also attached two pictures showing the weight difference. Surely Cura part is much heavier than the Simplify3d one. Also the finish is much nicer on Simplify3d.

An interesting note, when I change the surface mode to "Surface", it draws the lines perfectly, however, it creates an inner shell, doubling the overall thickness and the print time.

But as gr5 said, it really draws its strokes inside of the model-edge, not centered on the edge. It takes its nozzle-width into account. Similar to image-editing programs where you can stroke a selection with settings: stroke inside edge / centered on edge / outside of edge. Here it is inside.

I have recently bought Simplify 3D and I have to say it prints single walls without any issue. All I had to do set 'External Thin Wall Type' setting to 'Allow single extrusion walls' and the print came out amazing.

I printed a 25 mm³ cube and found that my printer is spot on.  But in the X and Y axis, that 25 mm prints at exactly 25.4 mm.

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To see how this file looks in Cura viewer, save the file for printing -without modifying anything, -then open the saved gcode file.

See pict.  This makes printing engineering parts impractical.  I don't know if any other slicer does this.  Simplify 3D is too expensive for me, and the others I've looked at have a terrible user interface.  Not at all polished like Cura.  Cura is much better, but I'll have to adjust all of my models to account for this SOP.  Simply scaling a model won't work, since only the outer-most features would be reduced by 0.4 mm, and others would be to a lesser extent.

1) I'm not sure if you know what 25 cubic mm means.  It's a volume.  If it is a perfect cube then it would be 2.9mm on a side.  Is that what you were trying to say?  I'm not sure what you mean.

5) What you show in the first photo - Cura can't do that - the way it thinks about inside and outside - it just can't do that.  Sorry.  People (including me) have been asking for that for about 6 years now.  Programmers say it's not going to happen.  Some day it will happen but don't hold your breath.  Actually there is a mode called "vase mode" that can do what you show in the first photo - but the way you do that is a hack.  You first give cura A *solid* model with the inside filled in solid.  Than choose vase mode and it will just do one pass around the outer wall just like you want.  You have to set the line width to how thick you want the walls and even if you have a 0.4mm nozzle you can do 0.8mm walls if that's what you tell cura to do but cura will do it in one pass.

The additional 0.4 mm is my nozzle width.  So what Cura does, is it places the center of the line exactly at the wall perimeter of the geometry.  So each exterior wall is going to be exactly 0.2 mm (or half the nozzle diameter) beyond the geometry of the model.  So when it is, say, a tube, with 0.4 mm wall thickness, Cura is stumped.  And when I put that on surface mode, it tries to trace both the outer wall and inner wall, thus drawing two walls instead of one.

See pict.  This makes printing engineering parts impractical.  I don't know if any other slicer does this.  Simplify 3D is too expensive for me, and the others I've looked at have a terrible user interface.  Not at all polished like Cura.  Cura is much better, but I'll have to adjust all of my models to account for this SOP.  Simply scaling a model won't work, since only the outer-most features would be reduced by 0.4 mm, and others would be to a lesser extent.

TappingSpeed

By the way you *can* print 0.4mm walls with a 0.4mm nozzle using Cura if you choose print thin walls but it still does 2 passes.

But as gr5 said, it really draws its strokes inside of the model-edge, not centered on the edge. It takes its nozzle-width into account. Similar to image-editing programs where you can stroke a selection with settings: stroke inside edge / centered on edge / outside of edge. Here it is inside.

3) "additional .4mm is my nozzle width" - okay so this is a common thing for people to worry about.  If you slice a solid 25mm cube and your line width is 0.4mm, cura is smart - it knows that the lines of filament will stick outside the nozzle by 0.2mm all around so it shrinks all the walls inwards by .2mm which should result in 23.6mm of movement in the gcode and a 24mm cube.  The people who wrote cura are pretty damn smart.

3) "additional .4mm is my nozzle width" - okay so this is a common thing for people to worry about.  If you slice a solid 25mm cube and your line width is 0.4mm, cura is smart - it knows that the lines of filament will stick outside the nozzle by 0.2mm all around so it shrinks all the walls inwards by .2mm which should result in 23.6mm of movement in the gcode and a 24mm cube.  The people who wrote cura are pretty damn smart.