How to print non-watertight models / 0mm walls?

[JaXXoN 0]

 

Hi!

 

Cura is an amazing tool with such a strong community so that over the course of the last three years I'm doing 3d printing,  I always very quickly found a solution on the web for any question I had. So I never needed to bother you here in the forum, before 🙂

 

Background:

 

I'm ultimately trying to 3d print RC model aircrafts with a single wall and a highly custom infill (for weight reduction). Additionally, there might be openings in the print.

There are quite a lot of tutorials on this topic and I had some success by applying the suggested 0.45mm thin walls to any structure that shall be printed as a single wall (assuming 0.4 mm line width).

 

However, for me, that only works for fairly simple geometries. It horribly fails when applying the 0.45mm "shell" or "offset" operation to complex SubD objects. It seems that the "Moment of Inspiration" 3D modeller I'm using is very bad a these operations. The tutorials typically mention that Solidworks is used, but this tool is very expensive.

 

Instead of trying working around this issue by proper shell/offset operation, I thought it might be a good idea if you could instruct Cura to simple assume that any surface in an stl file shall simple be a single wall. I.e. an upright rectangle should be printed as an upright single wall object. Unfortunately, Cure doesn't allow this.

 

I.e. if loading a sphere with a hole on its side (please see attached stl file and prepare screenshot), Cura always tries to fix that (see attached preview screenshot).

Under normal circumstances, that's a fantastic feature, but in my case, I'd rather like Cura to not fix anything and simple print the surfaces as a single walls.

This way, it would be very easy to do highly custom single wall prints.

 

I was looking trough the Cura settings for such an option, but wasn't able to find anything, so far. Maybe I'm just overlooking something?

 

Feedback is highly appreciated!

 

TIA and best regards

 

JaXXoN

 

 

 

 

 

 

 

spherewithhole.stl

[GregValiant 1,410]

That model won't print the way you want because it is not a solid in any way, shape, or form.  I tried different repair utilities but the "60 unsealed edges" around the hole always seal together and eliminate the hole and the model ends up solid.  It isn't so much that Cura is attempting to repair it as much as it is just an illegal model in it's original form and Cura is making a guess as to what it should be given the geometry Cura sees.

 

If the Shell function doesn't work (that can also happen with Solidworks, Inventor, Fusion, etc.) then you might have to break your design down into simpler pieces that can be modeled.  Those simpler pieces can then be assembled (union) in the design software into the finished skin of a part and then you can merge your interior rib structure.

Sometimes when a model refuses to "shell" it's possible to make a copy of the model, scale the copy to give you an approximate .45 wall, and then locate the copy within the original and subtract it from the original.  That would leave an outer portion that would be similar to a shell but probably wouldn't have the exact .45 wall thickness that a Shell operation would give you.

[kmanstudios 1,120]

Or use a mesh based system that will apply a shell in a way that works. There are give and takes on each program. Learning how and why each program does what it does is key. Choosing the program for what you want to do is going to follow that key. Since this was a mesh based object, I treated it as such.

 

It is teeny weeny though. Should be an interesting print at the scale it came in as.

 

Anyway, here is your sphere with hole fixed. It is now a proper 3D object. Without the depth of the wall, it was a mere 2D object.

spherewithhole3D.STL

 

This is a single wall slice. I followed the wall suggestion by @GregValiant as to wall thickness. Using a 0.4 nozzle you will get a single wall print such as this.

[GregValiant 1,410]

Nice.  Now that it's a proper 3D model it slices correctly.

 

I started with U-Control planes and eventually progressed to Radio Control.  They were balsa models that unfortunately never lost their "tree" instincts.  (Or just possibly I had progressed to my level of incompetence?  Nah!)

At any rate, at the end of a day of flying I could get 5 U-controls, or 2 RC planes, into a 5 gallon bucket.  It was big fun.

[kmanstudios 1,120]

6 minutes ago, GregValiant said:

At any rate, at the end of a day of flying I could get 5 U-controls, or 2 RC planes, into a 5 gallon bucket.  It was big fun.

Yes, but those are all 3D Objects 😆

 

[GregValiant 1,410]

Not when I got done.

[JaXXoN 0]

 

Hi!

 

Thanks for your valuable feedback!

 

I'm aware that Cura expects solid objects - otherwise it would have a hard time generating the infill 🙂

Just wanted to make sure I'm not overlooking the above described "surface to wall" slicing method. Would be a very useful feature, IMHO.

 

@GregValiant: I tried manually splitting the model, before, but I didn't had a whole lot of luck, because it's a fairly complex organic shape. But being motivated by this discussion, I tried a couple of different new ways and came up with a "brute-force method": separating the surfaces of the SubD solid and then applying the 0.44mm shell operation to each surface, individually. This yields a printable single wall model. The result is not perfect, i.e. the seems appear on the edges of the individual faces, but I guess I can live with that. BTW.: Making a union from the shelled surfaces yields the same result.

 

However, there's oen issue left: in the preview, the print-head moves forth and back over areas it already extruded to, increasing the print-time. This is even observable with the repaired "spherewithwhole3D.stl" provided by kmanstudios.

 

Feedback is highly appreciated!

 

TIA and best regards

 

JaXXoN

 

 

[kmanstudios 1,120]

You could always try spiralize. Just spitballing here.

[GregValiant 1,410]

Did you have combing turned on?

[Torgeir 280]

Hi there,

 

When I saw those comments, I’ll new there must be something interesting.. 😁

 

After reading in here about creating RC aircraft using plastic, -here is the other last topics about this in January, is found here:

 

This tread was started by @GAZZER, he might be interested in this tread?

 

 

So I found my experimental scrap box, as I’ve made a “few” print of that wingtip for a Spitfire. This is the file attached (the Spitfire tip) found first in the above link.

 

Ok., here is my scrap box (for wingtips)..

 

 

 

 

Next picture of the tip with failure(left) and a good one(right).

In this and the below pictures, you can see the broken "wing strings" at several places.

 

Next is the reverse side of the wingtip, failed left.

 

 

 

Last picture, looking inside the two wingtip one is full of strings..  (Testing testing 🙂 )

 

 

The upper one is the good one and the lower one is full of cobwebs (maybe there is a whole family in there?) 🤪

 

 

Here is what I did.

 

As I could see all the critical parts (strings & spares etc.) using Cura in preview mode to see inside the model. Cura “yelled out” here is a leakage! I could not find anything critical, except for some “floating” object and thought it might be a little windy place to be. (I could see the outside in between the lines from inside.) Joke aside.

 

After slicing this wingtip, some of the combined string-spares was broken/missing at the string part.

So, armed with Cura viewer (at that time -ver. 4.6.1), and some patience, I tested out some parameter that I thought might play a role in this problem.

 

Well, after some “failed” models and adjustments, I finally got some "break true" with this issue.

The solution was: Reduced the "Minimum Polygon Circumference" from 1 mm to 0.5 mm.

 

Here is the setting to be changed in Cura to make this print possible with good result:

 

Use “Normal -0.2 mm” profile in Cura 0,20 mm height and standard nozzle 0.4 mm.

(Note, Cura Arachne Engine Beta use “Normal -0.15 mm”, -if using this ver. change h=0.20 mm)

 

 

Here is the setting made to "normal profile -0,20 mm" used in Cura:

 

Quality setting:

 

Layer height 0.2 mm

Initial Layer height 0.27 mm

Layer width 0.35 mm

Cura will adjust the rest of the layer setting!

 

Walls setting:

 

Wall line count 1

(Nothing more to change here.)

 

Top/Bottom setting:

 

Top layer 0

Bottom layer 0

Cura will adjust the next layer setting!

 

Infill density:

 

Infill density set to 0%

 

 

Build plate adhesion:

 

Build plate adhesion type set to “Skirt”

 

Experimental:

 

Slicing tolerance set to “Exclusive”

Minimum polygon circumference set to “0.5 mm”

 

 

Hope all this can help someone.

 

Good luck.

 

Cheers

Torgeir

 

 

 

 

Edited July 20, 2021 by Torgeir
Added text.

[JaXXoN 0]

Thanks everybody for the fast response!

 

I read about the 3dlabs models - highly impressive work, there!

 

I tried it with the settings suggested by Torgeir, but the print-head is still dancing around with my "thin-wall model". Interestingly that doesn't happen with the above mentioned wing tip (thanks for the sample), the print-head moves pretty much as expected.

 

Please find attached a couple of screencast videos showing the print-head movement as per cura preview for certain models:

 

Cylinder_Solid: "traditional" solid cylinder with top/bottom thickness 0mm (no floor and ceiling) - head moves as expected.

Cylinder_ThinWall: thin wall cyclinder - head moves forth and back.

WingTip: Spitfire wingtip using the same settings as above - head moves as expected.

 

I'm wondering what 3Dlabs does to make the difference?

 

BTW.: Combing is turned off - I figured, it's bad for single wall prints, a while ago 🙂

Spiralizing didn't improve the situation.

 

Feedback is highly appreciated!

 

TIA and best regards

 

Bernhard

 

Cylinder_Solid.stl Cylinder_ThinWall.stl SliceVideos.zip

[JaXXoN 0]

 

Hi!

 

Quick Update:

 

The outer hull of the spitfire wing tip is actually a non-watertight 0mm surface! The inner structures are very thin solids. Instead of treating the thin walls as a single wall, Cura creates a perimeter around it (with some little space in between).

I interpret this as: the inner walls are treated as holes inside the outer hull. Please see attached screenshot.

 

I have created a simple example with a cylinder (not a solid - surface only) and some thin 0.05mm solid walls inside. Please see attached screenshots and 3dm/stl files.

 

The good news is that the print-head now moves as expected for the outer hull of the cylinder (it's not "dancing" forth and back).

 

The bad news is that when now trying to cut a hole into the cylinder, then Cura fixes it, again (as expected).

 

So I'm sorta back at square one.

 

best regards

 

JaXXoN

 

 

 

ThinWallExample.stl ThinWallExample-3dm.zip

[Torgeir 280]

Hi @JaXXoN,

 

The inner "added" part have way to much space to the cylinder.

The object is not seen as one part by Cura.

Can't you join them together?

It would be much better to have your project file, as we can see all the setting for your setup.

 

 

Torgeir

Edited July 20, 2021 by Torgeir
Added text.

[Torgeir 280]

Aha..

 

Need to dig some deeper..

 

Edit

Try make it closer.

 

Torgeir

Edited July 20, 2021 by Torgeir
Added text.

[JaXXoN 0]

Hi Torgeir,

 

In this example, the cylinder has an diameter of 20mm. The 0.4mm thick wall is inside this perimeter of the cylinder. The inner solids are 18.5mm in width and the 0.4mm walls are outside the perimeter of the solids - remember, these solids are actually holes or empty spaces, something where filament shall not be extruded to.

 

Means, the gap between the cylinder and the solids is 0.75mm and there is a small overlap so that the two perimeters will join in the print (please see Cura screenshot of the slicing). In my experience, this even works for gaps slightly bigger than 0.8mm because the filament gets squished a little bit and is slightly larger than 0.4mm. YMMV, though.

 

BTW.: If you make the gap smaller, then the perimeter of the inner solids cause the perimeter of the cylinder to "degrade". Please find attached a screenshot of a slice with a 0.6mm gap between solids and cylinder. This may give you a better bonding, but it will also cause the cylinder wall to be printed thinner, causing visual artifacts.

This is even visible for the Spitfire wing tip, if looking close enough (please see screenshot).

 

best regards

 

Bernhard

 

Edited July 20, 2021 by JaXXoN
Added screenshot for wing tip gaps

[Torgeir 280]

Sure agree, -but aren't you asking a little bit too much of an FDM printer?

 

Well, it's bed time here -long time ago..

 

Torgeir.

Edited July 21, 2021 by Torgeir
Error corrected.

[JaXXoN 0]

9 hours ago, Torgeir said:

but aren't you asking a little bit too much of an SLA printer?

 

I guess you mean FFF printer? And, actually, no 🙂

 

BTW.: I have pretty good results with another method, where a wing gets intersected/sandwiched by a honeycomb structure. Can be printed in vase mode (spiralize), is very light-wight and strong, but with a lot of visible artifacts - however, this gives the print a very distinct look.

 

Still, I think it would be a great feature if Cura could simple treat a surface in an stl file as a wall. Mathematically, it's not difficult to determine the endpoints of the line that results as the intersection of a triangle and the layer. I guess that slightly harder part is to concatenate the lines into a single "spaghetti".

 

[Torgeir 280]

Hi there,

 

Yesterday was a slow day..

I come to think that those stripes or artifacts may be caused by a tiny play I have in the X/Y axis - head.

With this "fast" printing this may play a role here, -but some places are also quite smooth.

However, this "good" print is kind of strong as I can twist a little with no "cracking" sound and weight only 17.7g.

When I'm looking at the "spare/string" design inside the wingtip, those edges are not parallel with the outer skin.

As this skin is just one tiny layer, such issues must be taken into consideration when designing such tiny profiles.

The glue effect vs printing temperature also play an important role here, all this is kind of complicated for sure.

 

To me this kind of 3D printing is the most interesting, so I'll keep experimenting in this area for sure.

 

Keep up the good works.

Thanks

Torgeir

 

[JaXXoN 0]

@kmanstudios: can you please tell me which meshing tool you used for applying thickness to "spherewithhole.stl" in order to create "spherewithhole3D.stl"? Maybe I can find some magic settings that work for me, too :-)
Are there other meshing tools you would recommend?

TIA and best regards

Bernhard

[JaXXoN 0]

 

Hi all!

 

I just stumbled over "Special Modes" -> "Surface Mode" -> "Surface", which does exactly what I was looking for!

 

The "spherewithhole.stl" file certainly won't print because there's only exactly one wall per layer - means, no top/bottom layers to fill the gaps. But that's what I asked for, maybe too exactly 🙂 BTW.: there's no "print-head dance" when slicing it this way.

 

I think the surface mode is very helpful in my case, i.e. I can add missing walls, manually.

 

Or maybe it's possible to do surface mode + top/bottom layers?

 

Feedback is highly appreciated!

 

TIA and best regards

 

Bernhard

 

 

[kmanstudios 1,120]

Be mindful of the gaps at the bottom. One wall on low slopes, like on the bottom and top areas, will leave gaps between lines. You can see it in the slice. But a slight change in topography and that could be easily solve the issue.

[JaXXoN 0]

4 hours ago, kmanstudios said:

Be mindful of the gaps at the bottom. One wall on low slopes, like on the bottom and top areas, will leave gaps between lines. You can see it in the slice. But a slight change in topography and that could be easily solve the issue.

 

Thanks very much for the fast response!

 

Can you please describe how the topology would need to be changed to fix the gaps?

 

TIA and best regards

 

Bernhard

 

 

[Torgeir 280]

Hi Bernard,

 

We're using "Adaptive Layers" to print overhang better, it's found under "Experimental".

The new Cura Beta version "Arachne Engine Beta", -have much better line width control.

 

But you'll need to tune a little.

 

Torgeir

 

[kmanstudios 1,120]

He is on a Draft original setting. So I am thinking tighter line heights.

 

Also to change the structure you would want to avoid curves that are too shallow to get a good resolution unless you go very tight with line height as well as using Adaptive Layers.

 

Depends on what your design requires as to how to construct the geometry needed.

[JaXXoN 0]

Hi!

 

I made some progress by adding an overlay that prints the bottom with "Surface Mode" "Both" and "Bottom Thickness" "0.8mm". This generates the bottom layers as required:

 

 

 

The only remaining issue now is that the overlay part doesn't flow smoothly into the surface only part:

 

 

I think that somewhat makes sense because in surface mode, I assume, a wall is placed +/-0.2mm around the surfaces, whereas in "Surface Mode" "Normal" , the surface of the sphere is the outer perimeter and the wall is generated inside the perimeter.

 

I tried to compensate that with "Horizontal Expansion" in the overlay, but it appears that this setting is completely ignored. Alternatively, I tried "Surface Mode" "Both", that should treat the overlay as both, solid and surface: the solid is sliced, but the wall for the sphere surface is missing.

 

Feedback is highly appreciated!

 

TIA and best regards

 

Bernhard

SphereWith2Holes.3mf