How deep is a locomotive inspection pit ? I dunno, but a quick enquiry on the DOGA e-mail board and after a little chat, received this from Colin:
I toddled down to Hither Green depot and sweet talked the guy in charge. I measured the pit to be 3' 6" deep.bottom to rail head.
So there we have it, in 4mm scale 14mm.
My pit has to be inserted from the bottom of the board so I cut some brick plastic to the right size and then made shorter Daler board walls and floor to cover the bits not in the woodwork.
Steps at the end were scratchbuilt from plasticard. They are a bit rough but hidden in the shed no one will notice. Step making is fiddly but easier here. I cut the sides and stuck them to the pit sides then joined them with strips of thin (0.5mm I think) plasticard and lots of solvent to weld the whole lot together.
And I did remember to check the construction fitted in the hole. It did with only a little extra filing...