Boolean Union inconsistent displayed object and the object property Type

I ran into a strange issue after doing a Boolean Union. I only noticed this after I exported to a STL for 3D printing. The printing app says there is a problem with the model and asks if I want the app to repair it.

I began investigating the Rhino model and found that the display for a small area on the object shows an open polysurface. However, the Properties tab for the object says, “closed solid polysurface”.

My actual model is somewhat more complicated, but I’ve attached a simpler model that shows the exact same issue. It should be fairly obvious what steps I followed to create the final object. I will note that the issue does not occur when I use a strictly Circular solid polysurface for the Boolean Diff in the 4th step in creating the object. It does occur when I use an Elliptical solid polysurface. I don’t know why that would make a difference.

Am I doing something incompatible with how Rhino does Unions? Or is something else going on?

BooleanUnion-01.3dm (874.7 KB)

Systeminfo:

Rhino 8 SR14 2024-12-10 (Rhino 8, 8.14.24345.15001, Git hash:master @ cdb74b46090a23fe242c51b288886f76467a741b)
License type: Commercial, build 2024-12-10
License details: Cloud Zoo

Windows 11 (10.0.26100 SR0.0) or greater (Physical RAM: 32GB)
.NET 7.0.0

Computer platform: DESKTOP

Standard graphics configuration.
Primary display and OpenGL: NVIDIA GeForce RTX 3080 Ti (NVidia) Memory: 12GB, Driver date: 11-6-2024 (M-D-Y). OpenGL Ver: 4.6.0 NVIDIA 566.14
> Accelerated graphics device with 4 adapter port(s)
- Windows Main Display attached to adapter port 0

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: 11-6-2024
Driver Version: 32.0.15.6614
Maximum Texture size: 32768 x 32768
Z-Buffer depth: 24 bits
Maximum Viewport size: 32768 x 32768
Total Video Memory: 12 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” 8.14.24345.15001
C:\Program Files\Rhino 8\Plug-ins\rdk.rhp “Renderer Development Kit”
C:\Program Files\Rhino 8\Plug-ins\AnimationTools.rhp “AnimationTools”
C:\Program Files\Rhino 8\Plug-ins\RhinoRenderCycles.rhp “Rhino Render” 8.14.24345.15001
C:\Program Files\Rhino 8\Plug-ins\rdk_etoui.rhp “RDK_EtoUI” 8.14.24345.15001
C:\Program Files\Rhino 8\Plug-ins\NamedSnapshots.rhp “Snapshots”
C:\Program Files\Rhino 8\Plug-ins\MeshCommands.rhp “MeshCommands” 8.14.24345.15001
C:\Program Files\Rhino 8\Plug-ins\RhinoCycles.rhp “RhinoCycles” 8.14.24345.15001
C:\Program Files\Rhino 8\Plug-ins\RhinoCode\RhinoCodePlugin.rhp “RhinoCodePlugin” 8.14.24345.15001
C:\Program Files\Rhino 8\Plug-ins\Toolbars\Toolbars.rhp “Toolbars” 8.14.24345.15001
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”

Thanks for your reporting, I’m seeing this issue about BooleanUnion as well. I will log it to our development engineer.

Please set the MergeCoplanarFaces = No while you run the command BooleanUnion, it will fix your current issue.

@habudg This issue will be fixed in Rhino 8.16.

That’s great!

RH-85347 is fixed in Rhino 8 Service Release 16 Release Candidate