If you're using the SketchUp Free web version or want to avoid paid extensions, you can use the tool.
Sketchup faces have a white (front) and blue (back) side. If your model has a mix of front/back on the same surface, Round Corner will create a "crack." sketchup round corner crack
If you follow the steps above—specifically the Scale Up by 100x method and switching to Smooth (Quads) with 3 segments—you will eliminate the crack permanently. For those who refuse to change their workflow, the native tool remains the only crash-proof solution in SketchUp. If you're using the SketchUp Free web version
Despite the ease of creating round corners in SketchUp, cracks can sometimes appear in your design. These cracks can be frustrating and may require some troubleshooting to fix. Here are some common cracking issues and their solutions: For those who refuse to change their workflow,
dialog to hide the segment lines and make the surface look continuous. Troubleshooting Common "Crack" Issues
When searching for a "proper" feature to round corners in SketchUp, users are usually looking for a tool that is robust, doesn't break the geometry (creating cracks or black faces), and is easy to use.