So I cut a revolved body in half along its axis using cut with surface (front plane as the cutting surface) and mirrored the body again (I did this to copy a lof of features I've done on one half of the body). Then a split line appears on the middle of the surface, but not on the the fillet, which stops the split line. I checked both "merge solid" and "knit surface" option when mirroring. It is like cut a sphere in half and mirror it, we should get a continuous sphere. But solidworks generates a split line on the surface and leaves fillet strip continuous. I am very fruastrated...

Anyway, a few other operations generates these unpleasant lines too, such as fill surface (even with tangent or curvature end conditions). Knit surfaces may work on pure surface but never work on surface of solid bodys because it generates a new surface (with split lines on it) instead of knit the original surfaces on solid body.

I know a lot of people have been wondered about this and how hard is it for solidworks to add a function to remove these lines on continuous surface?