Hi Mark, Yes the coal mine and the mine run modules which are both 2' x 8' are different and not based on the L girder - joist method. I did this mostly because they will never have to support a load (ME!!!), and I wanted them light enough to move without struggling. Additionally, since I knew I was going to attach the mountain profile back board (1/4 " plywood), I pretty much needed a frame member back there to screw into.
Yes, the frame for these 2 modules, is essentially a Box Frame, 8 foot runners on front and back and some cross-members at 90 degrees... With the exception of a few cross members everything is 1 x 4, actually 3/4 x 3 1/2. It worked out well that since I was going downhill at a 3% grade, 3 inches over 8 feet, I mounted the Mine Run box frame about 4 inches lower than the Coal mine and then worked all the scenery in on the grade, and built it up to meet the Coal Mine spurs and the road.
Also as I was up against the basement wall the back box-frame members sit on frame supports that are attached to the wall, and the front of these modules is supported by the main L-Girder Joist structure of the main layout. The mine run module slides right 1/4 inch and then pulls out, and the Coal mine slides out along the 8 foot axis.
I guess the biggest design element for me through out this process is to make modules that can "slide" on a lower but separate frame. I have seen entire modules built with their own leg assemblies, and I can't imagine fitting these together by having to move the whole thing with legs attached with much precision. Particularly on top of the 36 x 36 inch carpet tiles, I have installed in my train-room, and I would never trade in my nice padded cushioned carpet tiles for a concrete floor!
