To joint a hidden bookcase door hinge, first decide on the type of hinge to use, such as roller hinges, butt hinges, euro hinges or piano hinges. The hinge you choose must bear the heavy weight of a bookcase loaded with books. A weak hinge can cause a bookcase to sag.
For swing-doors, many carpenters prefer butt hinges. However, these hinges only conceal the door on a swing-in design, and the wear and tear of a heavy bookcase may necessitate repair or replacement over time. Pivot hinges are ideal, since they can support the heavy case and are easily concealed.
Before installing the pivot hinge, make sure the door swings free of the hinge jamb and can open to 90 degrees. Make a template for the hardware to make it easier to position and mark the locations of your mortises. Mount the bottom pivot spindle to the floor, and mortise the bottom bearing into the bottom of the door. Mortise a retractable jamb-mounted pivot spindle and finished cover head into the jamb plate.
Next, mortise a top guide into the top of the door. To hang the case, retract the top pivot spindle, and set the door perpendicular to the jamb on the bottom pivot. Position the door under the spindle, and insert the set screw to fasten the door in place. The top jamb pivot spindle should drop into the pivot guide. Finish the bookcase with false sides to completely conceal the door.