Couldn't boolean mirrored surface

Hello, could you please help me
I need combine two halfs in one - but BooleanUnion says ‘Objects do not intersect. Nothing done.’ althought one surface is a mirror from another…I need to create one surface without seam in between

issue.3dm (458.5 KB)

If you have just two surfaces that meet at an edge, use Join, not BooleanUnion.

thanx, but join don’t work either
Join create one polysurface but I cannot delete seam - “Mergeallfaces” says “Merged 0 polysurfaces. 1 polysurface could not be merged further.”

BooleanUnion does not merge things either. MergeAllFaces only works on planar faces. If you need to have it as one surface you will need to do something like the following:

  1. Duplicate the borders of both surfaces (_DupBorder)
  2. Delete one side
  3. Split the outer border curves at the mirror line and remove the two edges along the joint in the middle, then join the outer border back into one closed curve
  4. Use _UntrimAll to untrim the surface left over (fortunately, the full surface is still there, otherwise we would have to do something different)
  5. You will need to _ExtendSrf the opposite end of the untrimmed surface slightly in this case…
  6. Split the untrimmed surface with the duplicated border curves
  7. Delete the unwanted parts
  8. Use _ShrinkTrimmedSrfToEdge to clean up the extended end.

If you did not have the original underlying surface after _Untrim, you would have _MatchSrf the two untrimmed surfaces so they meet correctly in the middle then _MergeSrf them together into one. Then trim again with the borders.

Here is the result.

SingleTrimmedSrf.3dm (358.5 KB)

Wow, thanks a lot, sir, I get desired result
Unfortunatly I cannot open your file because of V5
and _ShrinkTrimmedSrfToEdge don’t give me any results, but my aim was to make it planar and after UnrollSrfUV i got perfect looking surface.
Can you please explain also why symmetry command don’t allow me to select edge (i know result will be not that perfect like your way but anyway )

Symmetry only works on untrimmed surface edges.

Here is the above file in V5 format for reference. SingleTrimmedSrfV5.3dm (358.0 KB)