Align might create a wrong or no solution because of the incorrect "opposite" setting. For closed faces like cylinders and tori this may make a difference in selecting from multiple possible solutions.
• Possible Solution:
◦ If the face normals of the change face and the reference face of the expected result is flipped by approximately 180 degrees you need to activate the opposite option.
Problem #2:
The geometry of the reference face is not large enough to come into contact with all neighboring faces of the changed face.
• Possible Solutions:
◦ Add the faces that do not touch the reference face to the changed faces (here the small side faces of the block).
◦ For freeform geometry use the Untrim command to enlarge the reference geometry until it intersects with all neighbor faces.
◦ If there is no connection (intersection) with all neighboring faces of the changed faces, the align operation fails.
Problem #3:
The change face may have a tangential neighbor that does not intersect with the reference face.
• Possible Solution:
◦ If you want to replace more than one face of a tangential face set you need to specify all faces of the face set at once (multi-face align)
