Alas, this is not a post about my model of the Hunter River Bridge. That project is languishing as work continues to focus on reconnecting modules of the layout following the house move last March. With the completion of the helix ( The Helix Part 2 - Lessons Learnt ), the effort has now turned to linking the helix to the branch lines of Mount Windeatt (lower) and Kingston Plains (upper). As the gap between the helix and branch line modules is actually the main passage to the central part of the layout, it was necessary to construct two bridges to facilitate these links. The bridges, as de facto extensions of the helix, are part of the 'back of house' portions of the layout and will not be sceniced.
The lower bridge is a lift out section. I had intended to build a lift up bridge like the upper level, but I used two timber dowels to locate one end and this impeded the necessary rotation of the bridge. As I was lifting the bridge out to facilitate the additional filing, scraping and chiselling to make it work, a voice in my brain kept saying that this was the solution, so a 'lift up' bridge became a 'lift out' bridge. I installed micro switches at each end to cut the power on the approaches when the bridge is not in place. At about 1100mm above floor level, this bridge is frequently removed to facilitate access to the main elements of the layout.
With the lower bridge lessons in mind, the upper level structure has been installed as a lift up swing bridge, no dowels this time. This time, there is only be one cutout switch controlling the approach from Kingston Plains. If the bridge is raised and a train approaches from the helix, there will be a collision but not a cataclysmic plunge to the concrete slab below. This bridge is around 1500mm above the ground and probably won't be raised as frequently as I have found that it is possible to walk underneath with only a relatively small bend of the head. Regardless, it can be raised if necessary.
The photo above attempts to show how these bridges are incorporated into the layout. The two branch line stations can be seen on the right, Kingston Plains on the upper level and Mount Windeatt on the lower. The edge of the helix can be seen on the left. One backdrop on the lower level has not been installed and the Singleton staging area behind Mount Windeatt is visible.