Help me out -- Carpentry question
I have two basic ideas, and one variation (at least) regarding how the upper section (Eagle Junction) will be constructed.
The overall dimensions will be 3 feet by 8 feet. That's big, and I will build it as a single section. Not ideal, but there's too much track on it to try to make it into two segments.
The section will lift off of what is below it (staging track loop) -- but I emphasize, that will NOT be an everyday occurrence. it's mainly being set up that way so that a) if in an emergency I need more access to the underside staging loop than I will have (and I do plan for fairly easy access from the sides, with openings or even little hatches in the fascia), I can as a last resort remove the upper section. Also, this design from the beginning has been premised on being able to be moved to a new home. While that's not by any means certain ever to happen I wanted to be prepared for the possibility.
Clearance for the staging loop underneath will be tight -- no two ways about it. The total rise from ground level track on the layout to the topside of this upper section is 5 inches (maybe a little more, if I'm lucky). So I need to keep the upper section to no more than 2 inches deep, and less if I can manage it.
The upper section will rest on a series of benchwork risers. I will probably use pegs to hold it all in place. I've got that worked out quite thoroughly and I'm confident that it will be sturdy and stable.
Wiring will not be underneath the unit. Instead, I will have plastic raceway attached to the siderails and use that to carry the bus wires. I would like to figure out how to bury feeders to track and switch machine on the top of the layout in some manner. I have some ideas about that, but let's put those aside for now. The point is to make it possible to address wiring problems without having to work at the underside of the section. I also anticipate including some kind of plug connectors to link the upper unit's bus wire with the rest of the layout bus wire. Again, that's not a big issue in my mind, so put that aside.
Ok, I think that covers the basics. So for constructing the upper section, here are the options I now see.
Idea No. 1: Between the 1 x 2 side rails, I would run a series of 1 x 2 cross pieces, laid flat, each end screwed and glued to the side rails. Their bottoms would be flush with the siderails' bottoms.
I could put as many of these cross pieces in as I want -- anywhere from 12-inch centers to 18 inch centers. I would lean toward more -- ie, smaller centers -- rather than fewer cross pieces.
Atop the cross pieces would be a single sheet of 1/4 inch plywood, creating a sort of tray.
At this point, the tray itself would have only 1/2 inch of open space (the cross pieces would take up 3/4 of an inch, the plywood another 1/4 of an inch, and of course the 1 x 2 siderails are only actually 1.5 inches high). So the thickest foam I could use would be 1/2 inch. Cork, landscaping, track, scenery, etc. all would be built on the foam.
I could put a sort of 1/4 inch trim around the top of the siderails, giving myself another 1/4 inch in the tray, so I could use 3/4 inch foam instead of 1/2 inch foam.
VARIATION: I could skip the plywood and just put plain foam on top of the crosspieces. If the crosspieces are on 12-inch centers that should be fine, I think. . Then I would be able to use 3/4 inch foam to begin with, or if I add the trim atop the siderails, 1-inch foam. The cross pieces, not the foam, would be what comes in contact with the wood supports holding the whole structure up.
Idea No. 2: The other idea would be to skip the crosspieces entirely.
IN that case, I would start with a 3 x 8 foot sheet of 1/2 thick birch plywood. I would put the 1 x 2 perimeter frame on top of the plywood, nailed or screwed and glued. Then I'd have a full 1-1/2 inches depth in the 'tray' and could use a piece of foam that thick in there.
My biggest concern is that, this second idea makes the entire upper section a full 2 inches deep. So unless I'm willing to increase the grade up to the upper level, clearance on the underside would only be 3 inches -- or strictly speaking, 2-3/4 inches because of the cork roadbed on the lower level staging loop. I don't run modern cars with their high profiles, so it's probably doable, but I have trouble flouting the NMRA 3.5-inch-clearance standard.
SO: Does either of these particular approaches seem better or worse? Is there a third alternative I am not seeing?
Is there some other alternative -- which accommodates the specific points mentioned at the beginning -- that you would suggest?