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How-To

Installing a Mortise Lockset

Mortise locksets combine security and convenience; follow these guidelines to install one.

By Mike Litchfield, Chip Harley
A door-boring jig will keep boring devices perpendicular to the door edge or face. This is crucial when boring the edge because there will be no more than 7⁄16 in. of wood on each side of the mortise casing. Moreover, a lockset set askew may not work correctly.

Mortise locksets house latch bolts and dead bolts in a single casing, so the door stile must be solid wood to receive this type of lock. If possible, order the door machined specifically for the lockset. If you intend to make the holes yourself, a door-boring jig will be a big help.

Mortise Lockset

Mortise Lockset
Mortise locksets combine security and convenience, because you can use a single key to operate both a latch bolt and a dead bolt.

 

PRO TIP: Because manufacturers often create a general hardware template for several different door styles, the template provided may be inaccurate. You may not need all the holes indicated, or you may need to reposition the template to accommodate a door edge bevel. So examine the door hardware and think things through before you mark or drill the door.

 

1. Using the template, mark the outline of the lock case on the edge of the door. Then mark a line in the exact center of the edge. Along this line, use a 7⁄8-in. spade bit to drill holes to the depth of the lock case. Overlap holes slightly.

Use an awl to mark the hole centers
Use the paper template supplied with your lockset to center face bores on the door stile and edge bores on the door edge. The template gives the exact setback and hole sizes. Use an awl to mark the hole centers. Prehung doors often come with lock cases prebored.

Drill the face bores
Drill the face bores, which are positioned with a paper template. Use a hole saw for the larger, key/cylinder hole and a Forstner bit for the spindle or thumb-lever hole. The small, round level taped to the top of the drill helps the installer drill perpendicular to the door face.

2. Use a chisel to square up the edges of the lock-case mortise. As you chisel, test-fit the lock case periodically to avoid chiseling away any more wood than necessary. When the lock case fits all the way into the hole, trace the outline of the main latch plate onto the edge of the door. Use a router to mortise the latch plate. If the door edge is beveled, adjust the tilt of the main latch plate to match the bevel beforehand.

Use a router and a template to mortise the latch plate into the edge.
Use a router and a template to mortise the latch plate into the edge.

Holes in the lock case should align with the holes drilled into the door face
Holes in the lock case should align with the holes drilled into the door face. If they don’t, use a rat-tail file to enlarge the face bores gradually.

3. Remove the lock case. Using the template, mark knob/spindle and key/cylinder holes on the face of the door stile. Use a hole saw to cut the cylinder hole and a Forstner bit or spade bit to cut the smaller spindle hole, holding drill bits perpendicular to the stile. Drill the holes until the point of the bit just starts through the other side. To prevent splintering of the stile face, back the drill out and finish drilling from the other side.

Use a chisel to square up the rounded corners
Use a chisel to square up the rounded corners of the latch-plate mortise.

For added strength and security, use 3-in. screws that will reach framing.
Strike plates are closely matched to the locksets they’re supplied with. Typically, the larger opening receives the dead bolt. For added strength and security, use 3-in. screws that will reach framing.

4. Reinsert the lock case, and screw it to the edge of the door. Then insert the spindles, slide the escutcheons over the spindles, attach the handles or knobs to the spindles, and see if they turn freely. Once they do, screw on all the trim hardware. Typically, door handles or thumb levers are 34 in. to 38 in. high.

5. You also will find a strike-plate template. Depending upon the depth of the strike-plate assembly, use a router or a combination of drill and chisel to mortise the plate into the jamb. To more accurately position the leading edge of the strike plate, rub pencil lead on the latch edge; when the latch is released against the jamb, it will leave a pencil mark. For greater security, buy a unit with a strike-plate reinforcer and 3-in. mounting screws.

Reinforced Strike-Plate Assembly

Reinforced Strike-Plate Assembly
Because 3-in. screws anchor this assembly to framing behind the door
frame, this strike plate can’t be dislodged by a kick.

Renovation 5th Edition

Excerpted from Renovation, 5th Edition (The Taunton Press, 2019) by Michael Litchfield and Chip Harley

Available in the Taunton Store and at Amazon.com.

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