Although you can purchase mass-produced interior doors inexpensively, they lack the charm of a hand-built, solid wood door. Building your own interior doors gives you the opportunity to customize them and to put the stamp of your personality on your home. Because doors are large objects, wood movement needs to be taken into account; if you build without allowing for it, you may find yourself with a cracked or sticking door.
Build a Plank Door
Measure the opening you are building the door for, using a tape measure. Use enough straight planks to make a panel that is an inch or two larger than this opening.
Flatten and square these planks with a jointer and a planer. If any of the planks are wider at one end than the other, make the ends the same width by running the plank through a table saw.
Glue the planks together to form a large panel by spreading glue on one edge of each plank, positioning them, and squeezing them together using bar clamps. Position the bar clamps alternately below and above the panel to prevent it from bowing in either direction. Leave the panel for several hours so the glue is dry.
Cut the panel to the size of your door opening either by running it through the table saw or by trimming it with a circular saw.
Set hinges into one side of the panel and either a doorknob or a latch into the other side. Screw the hinges into the side of the door with a screwdriver, drilling pilot holes first to avoid splitting the wood. Screw the latch onto the face of the door or drill a hole to fit the doorknob, following the installation instructions provided with new doorknobs.
Build a Panel Door
Measure the size of the door opening that you're making the door for, and take off 1/4 inch from the width and the height to allow the door some space. You can build the door tighter to the opening dimension in the summer, and allow more space in the winter, because the wood will be more swollen from humidity in the summer.
Build a frame for the door out of 2-inch-thick lumber. A traditional interior panel door will consist of four panels, the top two being taller than the bottom two. The frame that surrounds the panels consists of two exterior vertical stiles, a top and bottom rail, a center rail, and two center stiles, one of which runs from the top rail to the center rail, with the other running from the center rail down to the bottom rail.
Cut notches on the inside faces of the rails and stiles to fit the edges of the panels into them, using a table saw or router.
Cut a tenon on the end of each frame part that will be fitting into another frame element, using a table saw. Cut the tenons to a thickness that will fit into the notches that you cut for the panels. You'll need tenons on the ends of all the horizontal rails, which will be fitting into the sides of the vertical side stiles, and on the ends of the the two vertical center stiles, which will be fitting into the horizontal rails.
Make four door panels. Cut the panels on the table saw so that they are 1 inch wider and taller than the openings in your door frame; this will allow them to extend 1/2 inch into the notches that you cut into the rails on each side.
Assemble the entire door, put glue into the mortises and on the tenons, and clamp it together with bar clamps. Check for square by measuring diagonally from corner to corner across the door in each direction. These two diagonal measurements must be identical to make the door square.