I haven’t had this problem since v4. Random solid objects have their the surface direction facing inward. It is not obvious until I begin adding supports to an stl file. IIRC, in v4 the shade of gray alerted you to the surface direction. I can’t see any such indication in v8. Has somehing changed in a recent update?
Hi @hackettet
If these objects are NURBS, this should not happen. Rhino should always (or at least 99.9% o the time) leave closed solids with the normals outwards. How are these objects created? As @brvdln has already pointed out, you can turn on the coloring of backfaces in Rhino Options - the setting is also available in the Display tab:
-Jakob
In my personal experience, when a polysurface has alternating face orientations, it is usually due to the model coming from other software, or simply because the surfaces were built with loose tolerances and poor surface construction. When this happens, I lower the tolerance, and in some cases this approach resolves the issue.
It is in any case a red flag showing that something is fishy about the model.
I did a little experiment to duplicate the problem. So far the problem occurs when I extrude a shape along a line. I drew three squares, one with the “rectangle corner to corner” and two with the “polyline” tool, one clockwise and the other counter clockwise.. The two extrusions using the polyline tool had the surface directions pointing inward while the other had the direction pointing outward. When I capped them with the “surface from planar curvees” tool the directions didn’t change. I’ve been using exxtruded polylines to make complex ssurfaces (gears and structural elements) for years without a problem. This has only cropped up in the last two models. Thanks for pointing out that there is an option to visualize surface direction.
If you have a procedure for creating a closed solid object with one or more face normals facing inwards or in varying directions, please post the geometry and the procedure to create it and someone will check. That should not happen.
Attached is a series of screenshots showing the procedure where I made a closed object with the surface directions facing inward. I’ve been using this method for years without a problem. It has only been in the lasst few days where this problem has occdurred. Other methods for making solids don’t show this problem.
Rhino 8 SR26 2025-12-15 (Rhino 8, 8.26.25349.19001, Git hash:master @ c6182b1b71af690bf339ed38f9ccfc2fec2e46c3)
License type: Commercial, build 2025-12-15
License details: Cloud Zoo
Windows 11 (10.0.26200 SR0.0) or greater (Physical RAM: 16GB)
.NET 8.0.14
Computer platform: DESKTOP
Standard graphics configuration.
Primary display and OpenGL: NVIDIA GeForce GTX 1660 Ti (NVidia) Memory: 6GB, Driver date: 8-14-2025 (M-D-Y). OpenGL Ver: 4.6.0 NVIDIA 581.04
Accelerated graphics device with 4 adapter port(s)
- Windows Main Display attached to adapter port #0
- Secondary monitor attached to adapter port #1
Secondary graphics devices.
Intel(R) UHD Graphics 630 (Intel) Memory: 1GB, Driver date: 8-13-2024 (M-D-Y).
Integrated graphics device with 3 adapter port(s)
- There are no monitors attached to this device!
OpenGL Settings
Safe mode: Off
Use accelerated hardware modes: On
GPU Tessellation is: On
Redraw scene when viewports are exposed: On
Graphics level being used: OpenGL 4.6 (primary GPU’s maximum)
Anti-alias mode: 4x
Mip Map Filtering: Linear
Anisotropic Filtering Mode: High
Vendor Name: NVIDIA Corporation
Render version: 4.6
Shading Language: 4.60 NVIDIA
Driver Date: 8-14-2025
Driver Version: 32.0.15.8104
Maximum Texture size: 32768 x 32768
Z-Buffer depth: 24 bits
Maximum Viewport size: 32768 x 32768
Total Video Memory: 6 GB
Rhino plugins that do not ship with Rhino
Rhino plugins that ship with Rhino
C:\Program Files\Rhino 8\Plug-ins\Commands.rhp “Commands” 8.26.25349.19001
C:\Program Files\Rhino 8\Plug-ins\WebBrowser.rhp “WebBrowser”
C:\Program Files\Rhino 8\Plug-ins\rdk.rhp “Renderer Development Kit”
C:\Program Files\Rhino 8\Plug-ins\RhinoScript.rhp “RhinoScript”
C:\Program Files\Rhino 8\Plug-ins\IdleProcessor.rhp “IdleProcessor”
C:\Program Files\Rhino 8\Plug-ins\RhinoRenderCycles.rhp “Rhino Render” 8.26.25349.19001
C:\Program Files\Rhino 8\Plug-ins\RhinoRender.rhp “Legacy Rhino Render”
C:\Program Files\Rhino 8\Plug-ins\rdk_etoui.rhp “RDK_EtoUI” 8.26.25349.19001
C:\Program Files\Rhino 8\Plug-ins\NamedSnapshots.rhp “Snapshots”
C:\Program Files\Rhino 8\Plug-ins\MeshCommands.rhp “MeshCommands” 8.26.25349.19001
C:\Program Files\Rhino 8\Plug-ins\RhinoCycles.rhp “RhinoCycles” 8.26.25349.19001
C:\Program Files\Rhino 8\Plug-ins\Toolbars\Toolbars.rhp “Toolbars” 8.26.25349.19001
C:\Program Files\Rhino 8\Plug-ins\3dxrhino.rhp “3Dconnexion 3D Mouse”
C:\Program Files\Rhino 8\Plug-ins\Displacement.rhp “Displacement”
C:\Program Files\Rhino 8\Plug-ins\Calc.rhp “Calc”
C:\Program Files\Rhino 8\Plug-ins\SectionTools.rhp “SectionTools”
1: Starting Polyline
5: End Result
2: Extrusion curve
3: Extruded shape
4:Capped ends
Please post the file
Looks like you didn’t actually cap the ends, you just made planar surfaces without joining them to the rest. Try joining them or use the Cap command instead.
I found the problem. When I capped the ends, two caps were created at the start of the extrusion, one for the extrusion and a second for the curve. When jined, neither of the two caps were used so that end of the extrusion was open. I just have to remember to delete the original curves before capping the extrusion. I just never had to worry about that before. This problem doesn’t occur with some command generated curves such as corner to corner rectangle.
That’s not how that works, that’s not how anything works.
Please post the file.
There is no obvious new bug in Rhino, obviously. It’s your input or workflow.