The first step in mastering mortise locks is to understand the anatomy of the lock set. A standard mortise lock consists of a lock body, latch bolt, deadbolt, and a set of springs and pins housed inside the body. The lock body is the core that sits within the mortise cavity; the latch bolt is spring‑loaded and provides the “latch‑and‑hold” function, while the deadbolt is manually engaged for high‑security locking. The key cylinder, whether a pin‑tumbler or dimple, drives the internal cam that moves the deadbolt. Knowing how each part interacts is critical before you ever touch a door.
Installation begins with precise measurement. Measure the door thickness (typically 35 mm to 45 mm for residential doors) and the lock backset (the distance from the edge of the door to the center of the lock body, usually 60 mm). Mark the centerline of the lock on the door’s face, then transfer that line to the edge to locate the mortise cavity. Using a template, outline the cavity dimensions—commonly 45 mm wide, 20 mm high, and 30 mm deep. Cut the outline with a fine‑toothed saw, then deepen the cavity with a mortising chisel, removing wood in 2 mm increments to avoid splitting. The cavity walls must be parallel and the bottom flush with the door surface to ensure the lock body sits level.
Once the mortise is prepared, test-fit the lock body. The body should sit without gaps; if any are present, trim the cavity walls with a file. Insert the latch bolt and deadbolt, ensuring the latch face aligns with the door edge. Secure the lock body with the supplied screws, tightening them to 1.5 Nm torque to prevent over‑stress. Attach the strike plate on the frame, aligning the latch and deadbolt holes precisely. Finally, test the key cylinder: rotate the key to verify smooth operation of the deadbolt and latch, and check that the door closes fully without binding. Common issues—such as a misaligned deadbolt or a warped latch face—are corrected by adjusting the mortise depth or repositioning the strike plate.
The rest of this lesson (full video walkthrough + downloadable PDF + practice exercises) is available to enrolled Lock School students. Enroll →
Enroll → access the full 30-lesson curriculum