Adding and subtracting "seams"

I’m going to pose this question with simple scenarios:

  1. Lets say I have two cubes next to each other, and I union them. How do I get rid of the “seam” where the two cubes used to touch? There is an edge that runs down the middle of these co-planar faces.

  2. In SketchUp I can draw a rectangle on the face of a flat surface and extrude that rectangle out of the surface or into the surface. I can do the same thing in Rhino, but I have to split the surface with the curve, rejoin the two pieces to get that “seam” so that I can extrudesrf. In a more complex situation, if I have a polysrf I want to put a rectangular depression into, I need to explode the polysrf, split the target face with the rectangular polyline, rejoin all the faces into one polysrf and then extrudesrf inward. I know I could do boolean difference, but I like to avoid it. How do I add “seams” into a polysrf without this long workflow? “Seams” are useful to me because I can ctrl-shift click them and manipulate them.

If the seam is between co-planar faces, then MergeFace or MergeAllFaces will help (Cube example).

You can ‘add’ a seam using SplitFace.


Thanks Pascal. For the most part, splitface is working, but I am encountering a glitch. I made a square, extruded it into a cube, drew a smaller rectangle on one of the faces, split the face with the rectangle, but when I went to extrudesrf, its generating a separate polysrf. I made sure to have DeleteInput=Yes. I repeated several times with no success. I then tried exploding and joining the polysrf, and at that point extrudesrf was giving me the results I wanted (where the extrusion either adds or subtracts from the parent polysrf).

Is there somewhere I should report this glitch? I’m using the splitface command more, but I can’t get it to work correctly.

Hi Lawrence - can you send an example that does not work the way you like?


I’ve attached a sample file detailing the problem.
160111 Split Face Problem.3dm (207.7 KB)

Yeah, I see - looks buggy to me - thanks for the report. It looks like Explode first even helps, but in some cases it works as expected anyway. Still prodding this one…