Gluing up one side of the bookcase-door.

Grooves are milled into the sides of the bookcase-door called dadoes (day-doze). These dadoes provide strong support to the shelves and provide a channel to apply glue that holds the shelves to the sides.

Again, using clamping squares, we keep everything nice and perfectly perpendicular.

Once all of the shelves are glued to one side of the bookcase, the other bookcase-door side is glued in place.

It takes a lot of clamps to ensure there is an even amount of clamping pressure on every shelf.

After the clamps are removed from the sides, the back of the cabinet is similarly glued in place.

On the door frame, I use a specialized tool called a Domino Joiner that does only one thing, but does it very well. It drills oblong holes in wood to receive a wide, flat wooden dowel of sorts called a domino. Since the door frame is quite heavy and does not have a back like a bookcase to give it that third-dimensional support, it is necessary to make sure the four sides of the door frame are as sturdy as possible. Adding dominoes to the already glued & screwed frame sides will ensure the maximum amount of rigidity and strength where the panels meet. This particular hole is 2-3/8" deep.

A domino glued in place.

A domino glued in place. Once the dominoes have all been glued and hammered in place, I trim off the excess. Since this side of the door frame will be hidden from view and never seen by human eyes, it doesn't have to be pretty, just good.

I added an arched support to the top-back side of the door frame in order to further support and strengthen the doorway. 

The massive hidden door hinges that recess into the door and frame require large cavities to be carved into the wood. These are called mortises. To make the mortises, I will use a router and templates. The brass tube seen in the photo protruding out of the router is a bushing that rides inside of the templates. There are two depth levels in the mortises, so we need four templates, two for the frame and two for the door.

The first template in place. In order to put less stress on my router, I hogged out the majority of the wood with my drill and a large forstner bit. Then I will follow up with the router to finish removing the material and clean up the mortise.

Here is what the first mortise looks like after cleaning it up with the router.

The finished mortise and the hinge that will reside in it.

Test fitting the hinge in a perfectly carved mortise.

The hidden door bookcase mounted in the door frame. These concealed hinges are works of art and are butter smooth in operation.

The bookcase swings open and out of the way, allowing full access to the entire width of the doorway.