In Star Trek The Original Series, off-camera stage hands manually opened and closed the turbo lift doors.  Of course, these days, automatic doors are commonplace.  The most difficult part was getting the measurements correct, and completely hiding the sliding mechanism.  It was a big project.  The doors were hung last, and we had a big scare.  We had misjudged the carpet thickness.  The doors wouldn't open because there wasn't a gap between the bottom of the doors and the carpet pile.  There was too much friction.  After a few tense hours, we were able to finally raise the doors by two millimeters, which was  just enough to solve the problem.  Scotty would've been proud!