Sometimes the face exists, but it is reversed (blue instead of white). Right-click the area > .

To help you get this sorted out right away, could you tell me you are using, and whether this is a commercial extension like FredoCorner or the classic RoundCorner ?

This guide dives deep into everything you need to know. We will explore what makes RoundCorner indispensable, how to install and properly license it, and most importantly, how to solve the most frustrating modeling errors—including the dreaded "crack," disappearing surfaces, and geometry holes that can ruin your model.

: SketchUp has a known limitation where it cannot create very small faces (less than ~1mm). When rounding small objects, the tool may fail to close the new geometry.

The crack appears when the plugin fails to triangulate the cap correctly. The primary causes are:

Preventing the issue is easier than fixing it. Follow these best practices for seamless rounding:

If you'd like, I can also walk you through if the plugin has already ruined your progress. Share public link

Activate the and draw a diagonal line across the top face to see if it forces a split. If it does, your top face is not perfectly planar.

Select the group, activate the Scale Tool (S) , drag a corner grip, type 100 or 1000 , and press Enter .

Make a copy of the top face.

Hidden lines, internal faces, or duplicate vertices near the corner confuse the plugin's calculation engine. Step-by-Step Solutions 1. The "Dave Method" (The Scale-Up Trick)

The keyword includes the word which in the context of 3D software often refers to pirated or "cracked" versions of plugins. Using cracked versions of RoundCorner is a frequent cause of instability and "crack top" errors. While legitimate trial versions and paid versions (via Sketchucation) work reliably, cracked versions often:

SketchUp cannot create or maintain faces where the edges are smaller than approximately 1/16th of an inch (or roughly 1mm). When a rounding tool calculates a tight radius, the resulting tiny faces collapse into a single point, creating a physical hole or "crack" at the top junction.

If the "crack" looks like a jagged edge, select the arc or curve and go to the Entity Info Increase the (e.g., from 12 to 24 or 48) to smooth out the transition. Check for "Z-Fighting"

This gives you total control and eliminates the crack because the top face never touched the rounding algorithm.

Instead of searching for risky "cracked" software, you can use these free methods to achieve the same result: