LEVER FRAMES

Many different types of interlocking frame were used by the British railway companies. It is a whole subject for study in itself. Some were built in-house, whilst others were bought from outside contractors.

Interlocking was necessary to prevent signals for conflicting routes to be cleared, which could obviously cause a collision or mishap. The earliest designs used all sorts of ingenious methods to interlock the levers as each system was vigorously patented. Several cases occurred where one firm took another to court over alleged copying of their principles.

Stevens & Sons invented the tappet system of interlocking that became almost universal in use in later British interlocking frames. Remarkably, they didn't bother to renew their patent, and many manufacturers adopted this simple system as their standard with almost indecent haste.

The history of the contractors themselves is complex, too, and readers are referred to the Railway Companies and Contractors page for more details, dates etc.

This section does not attempt to describe in detail the methods of interlocking employed, but concentrates on the visual aspect - what the frames look like above operating floor level.

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