Whether you've decided to re-key an entry door by swapping out an exterior door knob or replace interior knobs to freshen the decor, changing the hardware is essentially the same process. There's little difference between the construction of interior and exterior door hardware, although the strength and quality of the material used to build the hardware will vary widely.
How Doorknobs Work
The visible parts of doorknobs are fairly simple. You see a knob or a lever on both sides of the door, a raised disk called the rose between the knob and the surface of the door, and a metal latch protruding from the edge. Turning the knob retracts the latch into a flat latch plate;and the latch engages with a matching metal strike plate on the door jamb when the door is closed. If the knob includes a lock, there is a keyhole on the outside and some form of lever on the inside to engage the lock.
The parts inside the doorknob have much more variety. Consumer-grade exterior locks only differ from interior locking knobs by being weatherproof and somewhat more sturdy. Security of these locks should be enhanced by installing a deadbolt. Cylinder locks provide additional security but are more difficult to install and replace. Regardless of the style, the working parts mount inside a large hole with a standard diameter of 2-1/8” that's bored through the door, while the latch is connected through a long hole drilled into the space from the door's edge. The inner and outer knobs connect with a spindle through the middle and a pair of screws. When you turn either knob, the spindle rotates and retracts the latch. When you release the handle, springs return the latch to its extended position.
Removing the Old Knob
1) Remove the screws holding the knobs together. For locking knobs, you may have to rotate the rose on the inside of the door, lining up holes in the rose with the screw heads.
2) When the screws are completely out, remove the knobs and roses on both sides. This will expose the interior workings.
3) Remove the screws from the latch plate on the door's edge, pull the latch bolt out through the edge. Fit the parts together and set aside to donate to an architectural salvage shop or recycling center for building materials.
Installing the New Knob
4) The distance from the edge of the door to the center of the hole is called the backset. Two different backset distances are common: 2-⅛ and 2-¾ inches. The new knob must have the same as the old knob to keep the latch bolt centered in the space. Many knobs in stores are adjustable to fit either backset. Consult the packaging for instructions to adjust the backset if needed.
5) Push the new latch assembly through the hole in the side of the door with the curved or angled face of the bolt facing in the direction the door swings when closing. The new latch plate will likely be the same size as the old one, but if it's larger, enlarge the mortise with a wood chisel.
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Most of the time the screw holes will line up, but it helps to “tighten” the old holes by pushing a broken wood match or toothpick into each hole, coated with wood glue.
6) Allow the glue to dry before screwing the latch plate into the side of the door. Swing the door until nearly closed to ensure that the latch lines up with the strike plate and is at the right orientation.
7) One knob is usually fixed to a spindle that goes through the hole in the door and a matching hole in the latch. The knob with exposed screw holes always goes on the lock side, usually the inside Thread the spindle through the latch bolt, then press the rose against the face of the door. If you can still see the hole through the door, adjust the backset distance and repeat. The knob must be centered for the rose to completely cover the hole.
8) Place the second knob on the spindle and verify that the knobs are correctly oriented: a lock knob or lever belongs on the interior, while a keyhole or lock release hole belongs on the outside. The installation convention is to have the widest part of the keyhole up. Compare to the directions that came with the new knob, as needed.
9) Test the knob and lock function before you close the the door. If the new latch will engage the strike plate already installed on the jamb and the finish is correct, you can leave it in place. If the old strike plate has a different finish or is damaged or if the new latch doesn't engage, replace the strike plate. The mortise for the strike plate may need reshaping, as above. Old screw holes that will be re-used or are too close to new screw holes are best plugged with wood and glue as above.
10) Verify that the door closes smoothly and locking knobs lock securely.
NOTE: Replacing mortise locks (flat boxes fitted into the edge of the door; rare except in old buildings) or cylinder locks requires different techniques. Mortise locks especially may exceed the kills of a novice.
