@fredo6 said:

That's probably the explanation. A face is created between the big and the small cube.

Actually, RoundCorner does not create the face, it is rather Sketchup that does it automatically (i.e. find_face).

Fredo

cool, thanks for the tip. I'm fairly new to sketchup; any advice on how I delete this internal face? Do I have to hide some visible faces and then delete the internal one or something?
Thanks!

Roundcorner is a very useful plugin. But I am having some trouble using it for my purpose. I am trying to create a model for 3D printing, and one of the design requirements is that sharp edges should be avoided. Another requirement, however, is that the object must be a "water-tight" solid in the end, and I am having trouble satisfying that with roundcorner. For example, if I try to round the corners on something like this:

The plugin appears to work, but when I group it, it doesn't become a solid. I use the "solid inspector" plugin to see what's wrong, and it shows me this:

When I zoom in to this, I can't see any problem:

Has anyone encountered this type of problem, and found a solution?
Thanks