Corbin Emhart

=Corbin Emhart =

The Emhart is a UL 437 rated pin-tumbler lock made by Corbin Russwin. The Emhart is best known for having interlocking pins that provide resistance to lockpicking and make the lock immune to key bumping attacks. The Emhart is one of the few pin-tumbler locks that uses axial rotation as one of its key control and pick-resistance features.

The Emhart is still produced but only existing systems are supported. Corbin Russwin lost a case filed by Medeco in 1975 which claimed the Emhart design, particularly the use of axial rotation, infringed upon Medeco's patents. The case was settled in 1977 and forced Corbin Russwin to pay Medeco royalties on each Emhart sold until March of 1987.

The Emhart has since been superceded by the Corbin Russwin Pyramid.

Principles of operation
The Emhart is a pin-tumbler lock that uses six pin stacks. The driver pins of the Emhart have a T shaped protrusion, with a matching gap on the top of the key pins. These two points interlock, requiring that pins move together until they are disconnected. When pin stacks are properly raised and rotated, movement of the plug causes the pin stacks to disconnect, trapping each driver pin above the shear line. Driver pins maintain their position by being trapped in grooves around the plug. These grooves double as protection against various forms of destructive entry, as well. The key contains cuts that mirror the grooves in the plug, allowing the plug to rotate completely while keeping the driver pins in the proper position.

The tips of key pins are chiseled at various angles and mate with angled bitting cuts on the key. These cuts provide axial rotation which is necessary to properly rotate the pin stacks.

The Emhart uses a variable MACS based on the angle of rotation between pins. Adjacent pins with the same angles use a MACS of 4, adjacent pins with different angles use a MACS of 3.

Dissassembly instructions
The Emhart is relatively easy to disassemble, but it cannot be disassembled in as many ways as traditional pin-tumbler locks. Most importantly, the plug cannot be removed with a traditional plug follower because of the interlocking pins and the ribbed plug. Pin stacks must be installed and removed from the pin chambers only.


 * 1) Remove the pin chamber casing and remove the pin stacks.
 * 2) Remove the cam or C-clip.
 * 3) Remove the plug.

Vulnerabilities
The Emhart may be vulnerable to one or more of the following:


 * Lockpicking
 * Impressioning
 * Decoding

Notes
 * The Emhart is immune to key bumping due to the interlocking pins.
 * Traditional picking techniques disconnect the pins and leave no easy way to reconnect them, effectively making the lock non-functional. Overcoming this requires that after the plug is rotated to open the lock the key pins can be raised and rotated back to a position where they can re-engage the driver pins.
 * Certain forms of destructive entry, particularly forced removal of the plug, are much harder due to the design of the interlocking pins and the grooved plug.