I joined two cubes to one cube.

enter image description here

and I used subdivision modifier to make the object smooth.

But the object divided into two parts.

enter image description here

How can I use subdivision modifier to joined object without dividing the object?


2 Answers 2


Once you've joined the two cubes the geometry of both cubes still exists. With your joined cubes selected go into Edit Mode (tab) and Select > All:

enter image description here

Then Mesh > Merge > by Distance. If the faces of the two cubes are close enough then this will merge them (and each of their four vertices) into one. There will still be one face inside that you probably don't want, select it and delete it:

enter image description here

With your Subdivision Surface modifier it should now look pretty much like this:

enter image description here


Join didn't change the meshes. If you want the two cubes to be replaced by a single object, you can select that object

  • go to edit mode

  • type A to select all

  • type M to bring up the merge menu.

    Merge menu

  • Select by distance from the popup.

NOTE: that only works because your two cubes are very close together. If they were further apart you would need a different technique.

Now you'll have one object but it will have an interior face, because merging the vertices didn't delete the extra face. While still in edit mode:

  • type ALTA to deselect everything

  • go to the select menu and select Select All by TraitInterior Faces

    Select menu for selecting interior faces

  • type X to bring up the delete menu.

    Delete menu

  • Select faces from the menu.

You should now have an object that looks like this in wireframe mode:

double cubes now one object

Now the modifier will work as expected:

subsurf applied to new object

  • 2
    $\begingroup$ Just a quick note on: "If they were further apart you would need a different technique." No, not necessarily. As long as the opposing vertices are closer to each other than the vertices connected to each other, you can adjust the Merge Distance until they merge together. I think it's a pity that people always use a lot of tools just with the default settings instead of showing what options you have. $\endgroup$ Jan 17 at 7:39
  • $\begingroup$ Good point. I was lazy and hid "adjust the merge distance" under "different techniques" in my mind. Thanks for pointing that out. $\endgroup$ Jan 17 at 14:47

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