After going all the way around the room I now need to complete the circuit with a lifting hatchway.
I was of course stupid to do this last as it is difficult enough without trying to get the levels on each side the same. I had to undo some of the woodwork that I first put together a few years ago in order to build out a base on which to mount the hatchway hinge side. I have used kitchen flap type hinges which are relatively narrow and allow the hinges to be separated later by removing the metal shaft.
The hatchway itself which is approx 85cm long (too long probably) is made of 12mm ply strngthened on each side by some 2 x 1. The hinges mount into the 2 x 1 through the ply for extra strength. I have made some stops for the hatchway to rest on when it is up, again not ideal but ok.
The whole thing is kept inline laterally by usine one DCC concepts alignment dowel pointing upwards from the base on the open side of the hatch (see the photos).
Finally I have put some wooden sides to the hatchway (painted gray to give the impression of bridge sides) to stop errant derailed trains running off the edge (a la the Tay bridge disaster). This is of course completely non-prototypical for the South of Banbury station but I am too old to go crawling underneath!