Thank you for sharing this Round to Square adapter here.
As for the question you raised about the difference between the STL and the process image in Luban, our software engineer said this is a bug in the ‘Linkage’ mode.
The simulation image of the BallInCase (left image) is not accurate enough, and the rotary module can carve the rectangular block according to toolpath, showing in the G-code.
But, there is a bug with “Linkage” mode, which means the model will be sliced in a different. This is the reason why you get a strange result.
Our software engineer is looking into this case and will try to fix this problem.
Sorry for the inconvenience.
Edwin