Tompson Patent Lock

William Tompson patented his lock design on 29 December 1808. The patent described a mechanism in which the lock acted in both perpendicular and horizontal directions, with the bolts retracting fully into the body of the lock when unlocked. This double-action movement is similar to that found on the earlier Turner Patent lock.

Tompson Patent locks are most commonly encountered on writing boxes and portable desks. Their principal advantage is that, when unlocked, the links and central locating peg retract completely below the surface of the lock plate, leaving it flat and unobstructed. This differs from many Bramah writing-box locks, whose links and locating pins remain projecting through the plate in both the locked and unlocked positions.

The lock plates are usually stamped ‘Tompson’, often accompanied by ‘Bir.M’, referring to Birmingham, and ‘GR Patent’ beneath a crown. Tompson is independently recorded as a patent lockmaker and key stamper in Bull Street, Birmingham, by 1818.

Some examples are fitted with an elaborate cast-brass escutcheon in which the keyhole is incorporated into a royal coat-of-arms design, with ‘Tompson Patent’ appearing in raised lettering.

Operating a Tompson Patent Lock

When the key is inserted, its side wards pass around the circular ward within the lock. This ward prevents an incorrectly shaped key from reaching and operating the internal mechanism.

As the key is turned anti-clockwise, the bit first engages a sprung lever which raises the bolt assembly. The links and central locating peg then rise above the surface of the lock plate.

As the key continues to turn, it engages a second sprung lever and moves the sliding portion of the bolt sideways into the locked position. A rectangular opening within the bolt allows the central peg to remain stationary while the links move laterally.

The lock is then fully engaged.

To unlock it, the key is turned clockwise through a full rotation. The horizontal movement is reversed and the links and central peg retract completely into the body of the lock, once again leaving the lock plate flush.

Tompson Patent lock and key. — Tompson Patent lock and key

Overhead view of a Tompson Patent lock plate stamped ‘Tompson Bir.M’ and ‘GR Patent’ beneath a crown. — Overhead view of a Tompson Patent lock plate stamped with ‘Tompson Bir.M’ (Birmingham) and ‘GR Patent’ beneath a crown.

Unlocked Tompson Patent lock interior showing the bolt, drill pin, circular ward and central moving peg. — Interior of a Tompson Patent lock (in its unlocked position) with the bolt, drill pin, circular ward and central moving peg in view.

Locked Tompson Patent lock interior showing the bolt, drill pin, circular ward, lever spring and central moving peg. — Interior of a Tompson Patent lock (in its locked position) with the bolt, drill pin, circular ward, lever spring and central moving peg in view.

Tompson Patent lock interior with the bolt removed, revealing the drill pin, circular ward, two sprung levers and central moving peg. — Interior of a Tompson Patent lock with the bolt removed. The drill pin, circular ward, two sprung levers and central moving peg are in view.

A Tompson Patent lock fitted into an antique jewellery box in rosewood with engraved brass inlay. VIEW THIS BOX →

Acknowledgement of William Tompson’s lock patent. — Acknowledgement of William Tompson’s lock patent taken from the ‘Titles of Patents of Invention Chronologically Arranged From March 2, 1617 To October 1, 1852’.

Tompson Patent Lock

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