After twenty or so years of using tappet frames, The Great Western Railway embarked on improving flexibility in interlocking design and developed a five-bar version. Alongside the increase in the number of bars, other changes were made to the frame and lever designs.

This paper explains, with the aid of diagrams, the changes that occurred, how it was operated and how it affected the way in which the signalman worked compared to the 3-bar type. The 5-bar locking rapidly became the Great Western's standard tappet interlocking both for new installations and as conversions from 3-bar.

Written by one of our members, this paper is key to understanding how mechanical locking operates and the principles explained are equally valid for other railway company's tappet locking. Modellers who wish to replicate prototype signalling and use it correctly on their layouts also need an understanding of interlocking and this is an excellent primer in the subject.

This signalling paper is supplied as a photocopied booklet. Copies are created to order - we don't keep piles of them on the shelves - so there can easily be a three week gap between you ordering and the booklet dropping through your letter box. The wait will be worth it!

Need this on a different media? Contact us via the link at the bottom of the page and we'll see what we can do.