When installing a doorknob —more correctly called a lockset— you need to drill two holes into the door. One is for the knobs and the spring-loaded mechanism they turn, and the other is for the barrel. In addition, you need to make a hole in the jamb into which the barrel fits. Lockset manufacturers have standardized their products, so you can install most with a 2 1/8 inch hole saw and a 7/8 inch spade bit. You'll find a template supplied with your new lockset that makes placing the holes a snap.
How to Cut a Doorknob Hole
Things You'll Need
Step 1: Mark the Centers of the Holes
Unpack the installation instructions that came with the lockset, and cut out the template with a pair of scissors. Fold the template around the edge of the door at the height you want the knob, which is usually in the center of the horizontal rail that separates the panels. Tape the template to the door so the center is about 36 inches off the ground and mark the centers of the lockset and barrel hole by making an indentation with the tip of a spade bit. Remove the template when you've made the marks.
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Note that the template offers two possibilities for the barrel hole —one for a 1 3/8 inch door and one for a 1 3/4 inch door. Choose the mark that corresponds to the door width.
Step 2: Drill the Hole for the Knobs
Insert a 2 1/8 inch hole saw into your drill and position the pilot bit on the mark you made on the face of the door. Holding the drill steady to prevent wobbling, drill through the door until the tip of the pilot bit emerges from the other side of the door. Finish drilling the hole from that side of the door. This procedure guarantees clean edges on both sides of the door with no chipping.
Step 3: Drill the Barrel Hole
Check the instructions to see which size spade bit to use for the barrel hole. Most interior locksets will require a 7/8 inch spade bit, but many exterior locksets require a 1 inch spade bit. Position the spade bit on the mark you made on the edge of the door and drill a hole that extends into the larger hole on the face of the door. Keep the drill horizontal and straight while you make this hole.
Step 4: Drill the Strike Hole
The best time to make the hole for the door strike is after you've installed the lockset. Put a little lipstick on the end of the barrel, close the door and let the barrel hit the jamb -- this gives you the position for the strike. Center the 7/8-inch bit in the mark on the jamb and drill about 3/4 inches into it. After drilling the hole, set the strike in position, draw its outline, chisel a mortise so you can inset it and screw it to the jamb.