Step 1: Review the Manufacturer’s Template
Every mortise lock ships with a paper or metal template that specifies the exact dimensions and locations for the mortise pocket, cylinder bore, thumbturn bore, and faceplate recess. Before making any cuts, read the template thoroughly and confirm that the template matches the lock model you are installing.
Identify the following measurements from the template:
• Mortise pocket height, width, and depth
• Backset distance (typically 2-3/4” for commercial mortise locks)
• Cylinder bore diameter and center height from the bottom of the lock case
• Thumbturn bore diameter and center height
• Faceplate dimensions
Confirm that the door thickness is 1-3/4”. Mortise locks for commercial doors are designed for this standard thickness. A door that is thinner or thicker will require different hardware.
Step 2: Mark the Door
Position the template on the door edge at the correct height. Standard lockset height places the centerline of the lever or knob at 38” to 40” from the finished floor, though this may vary based on project specifications or ADA requirements.
Tape or hold the template firmly against the door edge and transfer all markings:
• On the door edge, mark the top and bottom of the mortise pocket, the faceplate outline, and the centerline.
• On the door face (lock side), mark the center of the key cylinder bore.
• On the door face (opposite side), mark the center of the thumbturn bore.
Double-check all markings against the template before proceeding. Misplaced holes cannot be corrected without replacing the door.
Step 3: Cut the Mortise Pocket
The mortise pocket is the rectangular cavity cut into the door edge that receives the lock case. The method for cutting depends on the door material.
Wood Doors
• Drill a series of overlapping holes along the centerline of the mortise pocket to the required depth using a drill bit that matches the pocket width. Use a chisel and mallet to remove the remaining material and square the corners. A mortising jig or router with a straight bit can speed this process and produce cleaner results.
• Test-fit the lock case in the pocket. The case should slide in snugly without forcing. Remove additional material with a chisel or file if needed.
Hollow Metal Doors
• Use an angle grinder with a cutoff wheel to cut along the marked outline on the door edge. Cut carefully to avoid exceeding the pocket boundaries.
• File all edges smooth. Hollow metal edges can be sharp and must be deburred for safe handling and proper lock case fit.
• Test-fit the lock case. The case should insert fully with the faceplate sitting flush against the door edge.
Step 4: Bore the Cylinder and Thumbturn Holes
Using the hole saw at the diameter specified by the template (typically 1” to 1-1/4”), bore the key cylinder hole through the door face on the exterior or corridor side. Bore from one side only partway, then complete from the opposite side to prevent blowout and splintering on wood doors.
Bore the thumbturn hole on the opposite face of the door at the location marked from the template. The thumbturn hole is typically the same diameter as the cylinder hole.
After boring, clean all holes of debris and test-fit the cylinder and thumbturn components to confirm alignment with the lock case.
Step 5: Cut the Faceplate Recess
The faceplate must sit flush with the door edge. On wood doors, use a chisel to cut a shallow recess matching the faceplate dimensions and thickness. On hollow metal doors, the faceplate recess is typically already formed by the mortise pocket cut.
Place the faceplate over the pocket opening and trace its outline if not already marked. Remove material to the exact depth of the faceplate thickness so it sits flush with the door edge surface.
Step 6: Insert the Lock Case
Slide the mortise lock case into the pocket with the latch bolt and deadbolt facing the strike side of the frame. The faceplate should sit flat against the door edge with no gaps.
• Secure the lock case by driving the faceplate screws into the pre-drilled holes. Tighten evenly to avoid canting the faceplate.
• Verify that the latch bolt retracts and extends smoothly by pressing the latch tail or operating the hub with a screwdriver.
• Verify that the deadbolt throws and retracts fully.
Step 7: Install the Key Cylinder
Insert the key cylinder through the cylinder bore hole from the exterior or corridor side of the door. The cylinder tailpiece must engage the lock case’s cylinder hub.
• Thread the cylinder into the lock case or secure it with the cylinder collar and set screw from the interior side, depending on the manufacturer’s instructions.
• Test the cylinder by inserting the key and turning. The latch or deadbolt should operate smoothly. If the cylinder tailpiece is too long, it may need to be trimmed to the correct length.
Step 8: Install the Thumbturn
Insert the thumbturn assembly through the bore hole on the interior side of the door. The thumbturn spindle must engage the deadbolt hub inside the lock case.
Secure the thumbturn with its mounting screws or set screw. Test the thumbturn by rotating it to confirm the deadbolt throws and retracts fully.
Step 9: Install the Trim
Mount the lever or knob trim on both sides of the door according to the manufacturer’s instructions. Trim installation typically involves:
• Placing the interior and exterior escutcheon plates (roses) over the cylinder and thumbturn holes.
• Inserting the spindle through the lever hub in the lock case.
• Mounting the levers or knobs on each side and securing with set screws or through-bolts.
• Tightening all fasteners and verifying that both levers return to the horizontal position when released.
Step 10: Install the Strike Plate and Test
Mark the strike plate location on the door frame by closing the door and marking where the latch bolt and deadbolt contact the frame. Cut a mortise in the frame jamb for the strike plate and the bolt pockets.
Secure the strike plate with the provided screws. Test the complete assembly:
• Latch bolt retracts when either lever is operated
• Deadbolt throws and retracts with key and thumbturn
• Latch bolt engages the strike plate when the door closes
• Deadbolt aligns with the strike plate pocket
• Door closes and latches without binding or excessive force
• Both levers return to horizontal when released
