How to avoid gap after merging two objects I tried to merge two objects A and B, before merging, I use the snap tool to snap each other perfectly along the edges as shown in the screen shot, After merging, the A and B become one object, then I selected them all by hitting &quot;A&quot;, then beveling, I found the &quot;Green X&quot; area are beveled which I don't want to have, what should I do to make this face become one piece so there doesn't have any bevel in between?
Left White Mesh. A Cube with loop cuts and one face [extruded] in the z direction.  Thus having the edges you might need to control bevel operation.  Next 2nd White Mesh Selected. Edges selected and the bevel operator used.   These meshes are intended as crude facsimiles of yours.
At this time we think having a fresh start is easier than [join] operator.  Or at least equivalent.
Possible option. 3rd from left Blue image. Faces selected and [Face Dissolve] operator used for a ngon, on both sides. Yellow image on right. Inset faces.