When in doubt, scale up (to give math room) and increase segments (to smooth the math). Do not fight the crack; engineer your workflow to avoid it.

Struggling with the SketchUp Round Corner extension? 🧩

Go to View > Hidden Geometry . You may find that the "crack" is actually an unsoftened edge or a missing tiny triangle. Use the Line Tool to manually stitch the gap, then use the Eraser Tool + Ctrl to soften the new edge.

Round corner doesnt work correctly - Extensions - SketchUp Community

The "crack top" issue usually stems from one of three problems:

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