So while waiting for the other double slip switch to arrive to complete Rutherford Yard track work I decided to start building the new frame work for the extension to the duck under.
The decision to extend the duck under was to allow the new switch lead for Rutherford Yard to extend across the main aisle of the layout to the locomotive service facility above the dispatchers desk.
The original version of the mainline bridge crossing from Harrisburg to Carlisle Junction over the Susquehanna River was designed to be lifted out if needed. And since starting five years ago the lift out has maybe been out twice. So the decision to make it permanently fixed has been made.
The existing frame work is quite sturdy so it only requires a little more to be added too. The pine timber is 120mm x 19mm and is covered with 12mm plywood, the river contour will be cut out at a later stage.
First step was to add the extra pine frame work:
The new frame work and existing is screwed back into the major benchwork, and if really needed could be removed at a later date.
Next step was to add the plywood top:
The addition of the new switch lead required the deepening & widening of the lead running in the bench work next to the mainline. It also required the alteration of the plywood that was placed in the wall cavity to stop locos & rolling stock taking the long drop down to the floor.
Once the grade and alignment was set it was time to add the Midwest Cork Roadbed, then once this had set to the bench work the grade had to be levelled to remove any undulations.
Then when this was correct the track work was added and checked along with the radius of the curve.
When I was happy with the track, roadbed, grade and radius of the curve it was time to setup the location of the new truss bridge. Fortunately the new bridge will be the same Walthers - Single Track Truss Bridge, so setting up was a matter of using the existing one for reference.
Next stage will be the installation of the remaining cork roadbed and track work...