A door that's installed well closes tightly and quietly and doesn't swing open on its own. That means it's been trimmed to leave a very small gap next to the jamb, or, as This Old House general contractor Tom Silva explains, "about the width of a nickel." What he means is: Make it just under ⅛ inch. So measuring and trimming the door before installation must be done carefully and precisely. In the same vein, the various mortises on the door—the recesses in which the hinges sit or the lockset slides—must be carefully cut out. Too deep and the door won't close properly and might spring open. Too shallow and you'll get creaks and scrapes every time you move the thing. The key to a good mortise is a sharp chisel and a steady but light hand. This is not the time to bang and dig with all your strength. The good thing about doors these days is that you don't have to spring for the expense of solid wood to get its look and feel. Many doors are made from solid medium-density fiberboard (MDF) or are so-called "solid-core" doors, which means they have a veneer of wood or MDF over a core of particleboard or wood pieces.
They're not only better at soundproofing than hollow-core doors but more resistant to warping than solid wood. In fact, MDF is one of the most stable materials you can choose. However, if you intend to use a stain or clear finish on your door instead of painting it, you'll want to get one with solid wood or wood veneer. Trim the Door to Fit To determine the door size, subtract ¼ inch from the width and height of the door opening. Measure the door to see if it needs trimming. If the amount to be trimmed is less than ⅛ inch, plane it down. More than that use a circular saw. If you must to cut the height, trim the thicker rail at the bottom of the door. To trim the width, take evenly from both sides. To cut the door with a circular saw, place painter's tape along the cut line. Mark the line on the tape and score it with a utility knife to prevent chipping. With the saw braced against a cutting guide and its blade on the waste side of the line, trim the door. Tip: Bevel the door edges 2 or 3 degrees where it hits the stop so the door will clear the jamb smoothly.
Mark the Hardware Location Place the door in the opening and shim it until it's centered in the opening. Check for tight spots. Plane or cut it as needed. Return the door to its opening and shim it evenly all around. Mark the door where it meets the existing hinge mortises on the jamb. Also mark the door at the latch hole for the existing strike plate. This will show you how high to place the doorknob. About 36 inches up from the floor suits most people. You can adjust this measurement a fraction in either direction to center the knob on the door's middle rail, if it has one. Chisel out the Hinge Mortises Once again, remove the door and set it hinge side facing up.Take half and line it up at a hinge mark, knuckles toward the outswinging door face and its straight side ⅛ inch from the edge. Trace the hinge in pencil onto the door. Then hold the hinge edge against the face of the door under the outline and draw a line under it. This will be a depth guide for your chisel.
Score through the layout lines with a utility knife. Be careful not to cut deeper than the guide lines. Carefully make a series of cuts, or kerfs, between the scored lines with a chisel and mallet. Sighting the chisel from the door face, tap lightly until each cut is at the depth of the guide lines. Hold the chisel bevel side down, and plow out the shards between the kerfs. Once you've chiseled out the waste wood from the mortise, turn the chisel over—bevel facing up—and scrape the mortise clean and smooth. Check its depth and smoothness with a hinge leaf. It should rest squarely in the mortise and flush with the door edge. Finish the other mortises in the same way. Tip: To hold the door upright on its edge, put "feet" on it—screw long, wide scraps of wood to the top and bottom ends, resting tight against the floor. Drill for a Mortise Lockset To make a pocket for a mortise lock, first drill a series of holes, then chisel out between them to square off the recess.
These holes must be perfectly straight, so you'll need a guide to keep the drill in line. Since the drill is wider than the door, the best way to check this is to use plumb as a reference to align the drill with the door. Stand the door on edge with the latch-side facing up; check it for plumb. Make a drill guide from wood scraps. Add boards to project the guide from the door and clear the drill. Clamp the guide in place. Use the lock's template to locate the mortise holes. Mark the holes' centers with a nail. Drill the holes with an auger bit. Chisel out between the holes to square off the mortise. Then chisel a shallow recess for the lock plate. Drill for the Cylinder Lockset If you're installing a cylinder lockset, not a mortise lock, use a hole-saw kit to cut the necessary holes in the door edge and face. Be sure to adjust the jig for the right backset for your lock. The backset is the distance from the door's edge to the spindle. Tip: If you have a cylinder lock, use a hole-saw to cut the necessary holes.
Be sure to set the jig for the right backset for your lock. Locate the Spindle Hole Mortise locks require holes for the spindle and keyhole. New locks come with templates to locate these, but be sure you use the holes spaced for your lock's backset (distance from spindle to door edge). Line up the template and tape it in place. Use a centering punch or a hammer and nail to make a starting hole for your drill bit at the spindle location and the keyhole location (if applicable).Using a drill/driver fitted with a ¾-inch bit, drill through the face of the door at the spindle location. Use a ⅜-inch bit to drill two holes to make the keyhole. Tip: To keep the face of the door from splitting as you drill, hold or clamp a scrap block of wood against the door where the drill bit will exit. Hang the Door and Attach the Hardware Once all the holes and mortises are finished, prime and paint or stain and finish the door. Make sure to cover all six sides with finish so it's completely sealed and won't swell in high humidity.