The top track of the pocket door and the actual "pocket" are one side of the pocket door structure. The length of the jamb piece is affixed to the end of the top track, completing the entire framework. This frame of the pocket door is attached at the rear and the outside of the jamb piece to the studs of an abbreviated wall section, thus becoming part of the wall. Everything is squared up and the front opening of the pocket is anchored to the floor by means of the holes in that thin metal plate.
The inch to an inch and a quarter of the jamb piece sticking above the side rails of the top track are sawn off to make flush corners that you drywall around. (No need to cut notches around those little pieces as it would at first appear.)
Hang drywall right onto the horizontal strips of the pocket door framework. But be VERY certain NOT to use screws that will, in any way, penetrate those wood strips. They WILL scratch your door! The drywall butts to the top wood of the track piece, and just to the edge of the pocket framework; it does not overlap it.
Then, you just follow the directions to hang the door on the track, and just trim everything out to your liking.
HINT: There is just enough room to fit the door into the opening and to be able to hang it up on the track BEFORE you install the trim. The installed trim encloses the door to make it impossible to remove it or for the back edge of the door to be seen. Yes, you can get the door off later, if necessary, by first removing the trim.
The steps:
1.- Assemble the frame
2.- Build the wall to fit the frame into
3.- Install the frame
4.- Drywall the whole thing (excluding the door opening)
5.- Hang the door
6.- Install the trim (this can vary in type, size, and design)
7.- Run casing around the two ends and the top of the framework
The trim and the casing will hide the rough cut edges of the drywall.
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Of course, because there are many different manufacturers of pocket door frames, some of these instructions may vary slightly. But the construction concept remains the same.