Hi SUIYAN, for now you would be able to get more pieces to merge if you take care that their initial starting spheres were the same.

If you want to mirror or rotate a piece, do that on your curves but not the surface and then trim the one common surface with the transformed curves.

Pieces constructed in that manner will be able to merge.

- Michael

Thinks Michael

我偶尔这么做，但这样又需要额外计算旋转的角度或捕捉点，镜像平面等。我创建这个讨论只是单纯的想知道为什么会不同并且改进。
I occasionally do this, but it requires additional calculation of rotation angles or snap points, mirror planes, etc. I created this discussion simply to understand why it is different and to improve it.

祝好。
Best wishes to you.