Mortise Lock Product

Overview

A mortise lock is a complete locking mechanism routed into a rectangular cavity (mortise) within the edge of a door. Unlike surface-mounted locks, mortise locks are integrated into the door structure, providing a secure, finished appearance and exceptional durability. The lock assembly contains the pin-tumbler mechanism, latch, deadbolt, springs, and mechanical linkages—all contained within a single steel case.

Mortise locks are the professional standard for commercial buildings, office doors, apartments, and high-security residential applications. They are heavier-duty, more tamper-resistant, and more repairable than simpler latch mechanisms. A quality mortise lock can serve reliably for 30+ years, making them cost-effective despite higher initial installation expense.

The mortise cavity

Installation requires careful carpentry: the locksmith or door manufacturer routes a rectangular cavity into the door edge, typically 80–120 mm tall × 30–50 mm wide × 50–65 mm deep. The cavity must be straight and square; any misalignment will cause binding or uneven wear. The Lock Case is inserted into this cavity and secured with Fasteners.

The Faceplate covers the edge of the cavity, providing a finished appearance and preventing dust ingress. The bolt protruding from the case extends through a hole in the door edge to engage the Strike Plate on the door frame.

Lock case and internal mechanism

The Lock Case is a brass or steel body—typically 80–120 mm tall, 30–50 mm wide, and 50–65 mm deep—containing the entire working mechanism. Inside, the Case Body houses:

1. The Cylinder Unit: A 5-pin or 6-pin tumbler cylinder with a mechanical Tailpiece protruding from its rear.
2. The Latch Assembly: A spring-loaded Latch Bolt (angled ~45°) and a manual Deadbolt (straight).
3. Return springs (Latch Spring and Deadbolt Spring) holding both bolts to their rest positions.
4. A mechanical linkage (Bolt Link) connecting the cylinder's tailpiece to the deadbolt cam.

When the correct key is turned in the cylinder, the tailpiece rotates approximately 90°, mechanically driving the Bolt Cam. This cam either retracts the deadbolt (for remote locks on exit doors) or holds it in a retracted state (for passage locks used on interior doors).

Dual-bolt design

Most mortise locks use a dual-bolt design:

1. Spring latch: The Latch Bolt is a beveled bolt spring-loaded to extend partially (12–16 mm) into the frame strike. Its 45° angle allows the door to be pushed closed without a key—the angled edge compresses against the strike, and the latch automatically seats. This is push-to-lock convenience.

2. Deadbolt: The Deadbolt is a straight bolt requiring manual rotation (key or thumb turn) to extend/retract. It provides security: the door cannot be opened by simply pushing or bumping—the key or interior thumb turn must be actively manipulated.

When a user enters the building with a key and turns it in the Cylinder Unit, both the latch and deadbolt are usually retracted. When exiting, the latch extends automatically (via its spring), and the deadbolt can be manually extended via the thumb turn or remains retracted (depending on lock function). This gives security while preventing lockout.

Lever handles and spindle

The Lever Knobs are the visible external hardware—typically two matching brass or stainless-steel levers, one on the outside and one inside. These levers are mounted on Lever Hub sleeves, which are press-fit or bolted to the ends of the Lever Spindle.

The spindle is a metal rod passing through the full thickness of the door, connecting the inside and outside levers. When the outside handle is pushed down, the lever hub rotates, turning the spindle. The spindle's rotation actuates the latch-release mechanism inside the lock case. On passage locks (no key), either lever can open the door. On entry locks, the outside lever is often dummy (non-functional without the key).

Interior thumb turns or knobs (for deadbolt control) are independent of the latch spindle, using a separate mechanical path.

Pin-tumbler cylinder

The Cylinder Unit within the mortise lock is a standard pin-tumbler mechanism, functionally identical to those in padlocks or deadbolts. The rotating Plug contains the keyway and the Key Pins (bottom pins matched to the key's cuts). The stationary Bible (housing) contains the Driver Pins (top pins).

Turning the correct key lifts all pins to the shear line, allowing the plug to rotate approximately 90°. The plug's rotation is transmitted by the Tailpiece—a rigid stem protruding from the plug's rear—which mechanically drives the deadbolt via the cam mechanism.

A mortise lock's cylinder is often removable (after drilling out the retaining pin) for rekeying. This modularity is a major advantage: if a tenant moves out or a key is lost, the lock can be rekeyed without replacing the entire case.

Latch and deadbolt mechanics

The Latch Bolt is spring-loaded to its extended position. Its 45° bevel angle is engineered so that closing the door pushes the bevel against the strike, compressing the latch inward. Once the door fully closes, the strike's rounded upper lip allows the latch to pop out and seat, automatically securing the door. This is the principle of push-to-lock.

The deadbolt is not spring-loaded; it is held retracted or extended by friction or a detent ball. Manual operation (turning the key or thumb turn) overcomes this friction, moving the bolt from locked (extended) to unlocked (retracted) positions.

A spring (Deadbolt Spring) returns the bolt toward its locked position after the key is released, but the bolt settles in the position dictated by the cylinder's rotation. This design prevents the deadbolt from unexpectedly retracting due to door vibration or slamming.

Strike plate and installation

The Strike Plate is mounted on the door frame, flush with the frame's face. It has two holes: one for the latch and one for the deadbolt. The strike must align perfectly with the lock case; any misalignment causes the bolts to jam or miss the strike entirely.

Professional installation includes:

1. Routing the mortise cavity in the door edge.
2. Inserting the lock case and securing it with fasteners.
3. Installing the lever handles and spindle.
4. Routing a strike cavity in the door frame (or installing a surface strike).
5. Testing bolt engagement and adjusting the strike plate as needed.
6. Installing the faceplate and trim.

A reinforced strike plate (Strike Reinforcement) is standard for commercial installations, featuring a long vertical lip that wraps around the frame, resisting forced-entry attacks.

ANSI grades and standards

Mortise locks are classified by durability and security:

• Grade 1: Heavy-duty commercial, 3,000,000+ cycles, advanced security features.
• Grade 2: Commercial/light industrial, 1,000,000 cycles, mid-range security.
• Grade 3: Residential/light commercial, 500,000 cycles, basic security.

Most mortise locks sold for apartment buildings and offices are Grade 2 or 3. They meet ANSI/BHMA standards for drilling resistance, bumping resistance, and cycling durability.

Rekeying and servicing

A major advantage of mortise locks is repairability. If a pin breaks, a spring weakens, or the lock requires rekeying, a locksmith can:

1. Remove the cylinder (after unbolting the lock from the door or drilling out the retaining clip).
2. Replace the pin stack or rekey the existing cylinder using standard locksmith tools.
3. Reinstall the cylinder without disturbing the door, strike, or lever handles.

This modularity means a mortise lock can be maintained and adapted throughout its lifespan, extending its useful life and reducing replacement costs.

Variations and options

Passage locks: No keyhole, just levers. Interior doors (bathrooms, bedrooms) where security is minimal.

Entry locks: Keyhole on the exterior, thumb turn on the interior. Typical for residential main doors.

Office locks: Interior keyhole on both sides (keyed alike), used for privacy without external security.

Master key systems: A mortise lock can be pinned with master pins and key wafers, allowing a master key to open multiple locks while individuals retain unique keys.

Heavy-duty commercial: Enhanced deadbolts, reinforced cases, anti-drilling features, and high-security pins.

Materials and finishes

The Lock Case is typically steel or ductile iron. The Lever Knobs and Faceplate are available in:

• Polished brass: Classic, warm appearance; requires periodic polishing to prevent patina.
• Satin chrome: Modern, brushed metallic finish; low-maintenance.
• Stainless steel: Corrosion-resistant, suitable for wet environments.
• Oil-rubbed bronze: Rustic, hand-aged appearance.
• Matte black: Contemporary, blends into modern doors.

All these are cosmetic choices; the internal mechanism remains identical.

Cost and lifespan

Residential mortise locks cost €150–350 per set (case, handles, cylinder, strike). Commercial-grade locks cost €250–500. Installation labor adds €100–250 per lock.

A well-maintained mortise lock lasts 30–50 years. Replacements typically occur due to cosmetic wear (handle patina, finish fading) rather than functional failure. Many historic buildings retain original mortise locks from the early 1900s, still functional after 120+ years.