On the layout's second anniversary, the objective was to build the track support in the center section of the layout. I clamped some temporary vertical spacers to the layout structure and placed a piece of 1/4-inch plywood on top of them. I then traced where the outside of the subroadbed was to be. You might be able to see some faint pencil lines in the photo.



After rough-cutting along the pencil outline, I placed the subroadbed plywood on the layout structure. I traced the outline of the plywood onto the layout's structure so that I knew where to place the vertical spacers that will hold the plywood in the correct location. The center section will have one track going down a little over an inch and one track going up a little over an inch, thereby providing about a two-inch clearance between the two tracks further down the road, so to say.



I glued and screwed a block against the edge of the existing mainline subroadbed. The block was placed so that the plywood, and the cork I will place on top of it, comes out level with the bottom of the existing ties. Here the plywood is dry-fitted to verify the height.



I cut a collection of pieces of 3/4-inch plywood to serve as the vertical spacers that hold the plywood up at the right height. Using clamps and levels (a 24-inch one and the 10-inch one shown in the photo) I lined up each of the vertical spacers. They were all referenced from the floor to dictate their pre-calculated height.



The vertical spacers in the back of the photo are all level with the existing mainline. There will be a turnout in that location, and I wanted to make sure that it was nice and level. The two vertical spacers in the foreground are the top and bottom level supports in their final position. The center vertical spacers were placed such that they are vertically in between the two ends. There will be a grade of slightly more than 2% for both of these tracks, but I think that should be manageable since I will be running fairly short trains.



The photo below shows all the vertical spacers in place. I used wood glue to attach them to the layout structure. The tops of the vertical spacers were cut at a slight angle to better support the plywood subroadbed. Little arrows drawn at the top indicates the high side of the vertical spacers.