While replacing a door into an existing opening requires few tools, it does require patience and care. Most interior doors have hollow cores and can be unforgiving for certain types of mistakes.

Step 1

Remove Knob and Lock Set

Working from the hinge side or rear of the door, take out the door knob and existing lock set.

Step 2

Remove Hinge Pins

Next, remove the pins holding the hinge knuckles together. Start with the bottom hinge and work your way up. Once you’ve removed the pins, it’s a good idea to place them along with all of the other hardware in a container in a safe place.

Step 3

Remove Door From Hinge Knuckles

Using both hands, lift the door off the hinge knuckles. Leave the wall-side knuckles attached to the door jamb. You’ll want these in the same position so that your door will align properly.

Step 4

Trim Door to Correct Size

Lay your new door across two saw horses with both ends and sides hanging off somewhat. Place your old door on top of the new one, you’ll use the old door as a template to help you trim your new door to size.

Step 5

Make Sure It's Flush

Remove the door-side knuckles, then align the top edge and hinge side of the two doors so that they’re flush. Keep all of the screws and hardware in a safe place for re-installation.

Step 6

Trace the Door

Using a pencil, trace the outline of the old door’s width and height onto the new one.

Step 7

Cut the New Door to Size

Remove the old door and cut the new door down to size. If you have more than 3/16” of an inch to remove, you can use a circular saw to do so. If you’re not steady with your saw, you can use a straight edge as a guide. Go slowly and make a long, clean cut. If you have more than an inch to remove, take half off the top and half off the bottom.

Step 8

Use a Handplane Tool ... If Necessary

If you only have a small amount to remove, a handplane is a better tool for the job. Additionally, if you need to clean up your circular saw cuts, you can use the handplane to square everything up neatly.

Step 9

Transfer Your Hinge Mortise

Lay the old door back on top of the new one, and transfer your hinge mortise, lock set mortises, and door hole outlines. Use a combination square to lay out your mortises, making sure that you’re transferring the proper width and height of the outlines.

Step 10

Score the Outer Edges

Using your utility knife with a sharp blade, score the outer edges of your mortise outlines. is will help you avoid tearout when you begin to work with your chisel. Make straight. deep score lines and be careful not to mar the finish on your door.

Step 11

Make Perpendicular Cutlines

Start by making cutlines perpendicular to the grain of the door. Hammer down to the depth of your hinge knuckle’s mounting plate. You’ll want that plate to be flush with the doors edge.

Step 12

Mortise and Repeat

With your chisel’s beveled edge flat against the door’s edge, gently tap to remove material within your score marks. You want to make a nice flat surface for your hinge to lay into. Go slowly and test-fit your hinge a few times until you get it mounted flush. If you accidentally go too far, you can place a thin wooden shim under your hinge to bring it back flush with the edge of the door. Repeat the mortising process for the other hinge along with the lock set.

Step 13

Drill Door Holes

Next you’ll need to drill the hole for the door knob and the lock set. Using a hole saw that is the correct diameter for your knob, gently drill out the hole for the knob. Then, using a spade bit, you’ll drill a hole through the lock set mortise into the knob’s hole. Make sure not to penetrate the back edge of the knob hole. At this point, you can apply paint or finish to your door if desired.

Step 14

Install Your Accessories

Install your hinge knuckles, lock set and door knobs. Drill pilot holes for your hinge hardware so that you don’t accidentally split the door’s edge.

Step 15

Hang your Door

Hang your new door and test-fit everything. If your door sticks, make a mark on the edges where it’s not closing flush. You’ll need to take the door back down and shave some material off using your handplane until the door opens and closes freely. If your knob and lock set are loose, you can bend the striker plate outward slightly, or unscrew the knob and make any necessary adjustments until your door is opening and closing freely.

Step 16

Your New Door is Ready for Use

Once your door is properly adjusted, you can re-insert any remaining hinge pins and install any other decorative hardware or door stops.