Rivet counter

[Peter_T1958]

It's already in the stl.file. With my clumsy CorelCad program I am able to modify the system variable up to the ratio «10» (normally I am working with the ratio «6»).
This increases the file size noticable, but in this case the outcome remains the same...

[Hauk]

It's already in the stl.file. With my clumsy CorelCad program I am able to modify the system variable up to the ratio «10» (normally I am working with the ratio «6»).
This increases the file size noticable, but in this case the outcome remains the same...

Hm. Have you looked into Autodesk Fusion? Its free for Hobbyists, and the free version have al the bells and whistles we need for making 3D drawings for printing.

Is this something that pops up in the STL, or is the problem already visible in the native file you are working with?

[Hauk]

You might have asked the Oracle yourself, but here is what ChatGPT-5 have to say on the matter:

Eliminating Facets on Large Curved Surfaces in STL Files from CorelDraw/CorelCAD

The Problem

When designing 3D objects with large-diameter curved surfaces in CorelDraw or CorelCAD and exporting them to STL format for 3D printing, the resulting file may show visible flat segments (facets) along what should be smooth curves.
The issue is apparent in the STL viewer before printing, which means it originates during export — not in the printer or slicer.
Why It Happens

The STL file format does not store true curves. All curved geometry is approximated by a series of flat triangular faces. The smoothness of the curve depends on the resolution of this tessellation process — how finely the software divides the curve into straight segments.

    Low tessellation resolution = fewer, larger facets → visible flat edges on cylinders, domes, and arcs.

    High tessellation resolution = more, smaller facets → smooth appearance.

If the export settings are too coarse, even a perfectly drawn circle will look polygonal.
Solution 1 – Increase Tessellation Resolution in CorelCAD

CorelCAD offers commands and settings to control mesh smoothness when exporting to STL.

Step-by-step:

    Set drawing units

        Tools → Options → Drawing Settings → set to millimetres or your working units.

        Ensures tolerances are scaled correctly.

    Increase curve display resolution

        Command: VIEWRES → set to 20000 (maximum).

    Increase mesh facet resolution

        Command: FACETRES → set to 10 (maximum).

    Adjust STL export tolerances

        Command: STLOPTIONS

            Chord Height (Deviation): 0.01 mm or less
            (Maximum distance between the mesh facet and the true curve)

            Angle: 1° or less
            (Maximum angular step around circles)

            Output: Binary STL for smaller file size.

    Export to STL

        Command: EXPORT or _STLOUT

        Select objects and confirm STLOPTIONS settings.

Result: Curved surfaces will have facets much smaller than the printer's resolution, making them appear smooth in both the STL viewer and the printed object.
Trade-off: File size will increase.
Solution 2 – Use a CAD Program That Keeps Curves Until Export

If you are working in CorelDraw only (without CorelCAD), curves are flattened early in the process, with no control over tessellation quality.
To preserve curve precision:

    Export your 2D paths from CorelDraw as DXF or SVG.

    Import into a CAD program that uses NURBS or parametric geometry (e.g., FreeCAD, Fusion 360, Rhino).

    Extrude or revolve your shapes in the CAD program.

    Export to STL, setting chord height and angle tolerances as in Solution 1.

Benefit: Curves remain mathematically exact until the very last export step.
Solution 3 – Post-Process the STL

If the coarse STL has already been generated and the original geometry is unavailable:

    Use MeshLab → Filters → Remeshing, Simplification and Reconstruction → Subdivision/Smoothing.

    Or use Blender to subdivide and smooth the mesh.

Limitations: This increases polygon count but cannot perfectly restore the original curve.
Key Takeaways

    STL is always faceted; smoothness depends on facet size relative to printer resolution.

    For CorelCAD: VIEWRES = 20000, FACETRES = 10, Chord Height ≤ 0.01 mm, Angle ≤ 1° are practical maximums.

    For CorelDraw: export to a proper CAD program before creating the STL.

    Higher resolution = bigger file, but no visible faceting.

If desired, a CorelDraw → FreeCAD → STL workflow can be documented that ensures mathematically perfect curves until the final export stage, completely removing visible facets in large curved surfaces.

[Peter_T1958]

Havard
Thanks a lot for your input. Up to now I never used KI to search for solving problems. Seems so I should change that habit...

For CorelCad the advises are :
- VIEWRES = 20000
- FACETRES = 10
- Chord Height ≤ 0.01 mm
- Angle ≤ 1°

Although the commands are a bit different, I tried them out. Some were working orther failed. So I couldn't adjust the «chord high» and the «angle». Alas the result remained the same!

In my 3d-Tool viewer it was very easy to smoothen the curves, but (of course) this doesn't influence the original file.



Perhaps I sould try to find a solution with "blender"!?!

[Lawrence@NZFinescale]

I'm not sure how simple Blender would be assuming you started with an .stl.

I had a quick play myself and it wasn't easy. Very easy to smooth curves and to keep the desired edges sharp, but not both at the same time.

Starting with a quad based model would be easier I suspect. You really want to be sorting faceting before converting to triangles.

[Peter_T1958]

I'm not sure how simple Blender would be assuming you started with an .stl.

You were right, that approach did not work! However, a brief look at the today's delivery showed, that things are not too bad. I removed the supports relatively roughly and especially the big fundation elements are still bent out of shape. At least it becomes obvious, that this would become a big gun...

[finescalerr]

The imperfection is barely noticeable and paint may further camouflage it. I also wonder how resin castings from such a master would look. In our little modeling society perfection is always the goal so I hope you devise a way to achieve it. -- Russ

[Lawrence@NZFinescale]

I'm not sure how simple Blender would be assuming you started with an .stl.

You were right, that approach did not work! However, a brief look at the today's delivery showed, that things are not too bad. I removed the supports relatively roughly and especially the big fundation elements are still bent out of shape. At least it becomes obvious, that this would become a big gun...

That looks OK - Always good to get some paint on too as it's hard to really tell until you do, but paint generally improves things.

If you do decide you need things to be better, the approach I use (albeit for different reasons) may help:

Draw in CAD.
Export in a way that the parts (ie bolts/rivets etc) remain separate.
Redraw the parts in Blender that you need to modify based on the CAD pattern
Delete/hide the original problematic CAD parts and export as stl.
[/list]

This is the approach I use for wood grain on the wagon planks.  The wagon is exported as OBJ (stl works too I think, though you may need to export as a more than 1 file). In the cad model planks are separate so I can export so that individual parts stay as distinct objects (a bit painful as there are many objects) or just export as 1 piece.  If the latter the parts are still distinct in edit mode and easily separated. Redrawing a board is extremely easy of course. Adding grain and distorting/distressing boards is far easier on a plain board comprised of quads compared to a triangulated board that is unhelpfully complex due to surface bolt detail etc.

In your case you'd just be redrawing the parts where faceting is a problem.  But hopefully you don't need to worry!

[Peter_T1958]

I found some time to continue on this project. That thing gets bigger and bigger. One point that is often overseen in kits, but at a calibre of this size it is  absolutely necessary to replicate : the rifling. My idea is to print the inner lining of the barrel separately to avoid supporting structures.