I'll be building an around the walls shelf layout 24" wide for HO trains. I'm planning on laminating 2 sheets of 1" foam and then laminating this to some thickness of plywood. I'll be doing "cookie cutter" with the foam to make it easier to shape landfroms and roadbed and there will be some spots where I will cut all the way through the foam for a riverbed from backdrop to aisle. Assuming 16" centers for shelf supports how thick does the plywood need to be? I can do a ledger board arrangemnt on the walls to help support the spans between brackets.
Modeling the Cleveland and Pittsburgh during the PennCentral era starting on the Cleveland lakefront and ending in Mingo junction
Can you get 2-inch thick foam where you are, instead of laminating 2 one-inch thick pieces? It will save you some work.
I use a 2-inch foam base for my layout. On Phase 1, I used 16-inch separation for rafters. On Phase 2, I increased that to 18 inches. The foam itself is very stiff, and needs no plywood at all. If you're going to cut through the foam, you may want something below it, but a complete base of plywood is not necessary.
It takes an iron man to play with a toy iron horse.
I use a rather different system; a sandwich of thin foam over thin plywood, in the form of cookie cut roadbed. There is no solid 'tabletop' above the L-girders; landforms are made (initially) with zip-textured hardshell.
IMHO, there are only two reasons to use plywood under a foam 'tabletop:'
Some modelers claim that foam over plywood is quieter than either foam or plywood alone. Since I haven't experimented much with either alternative, I can neither confirm nor deny that.
Chuck (Modeling Central Japan in September, 1964)
Since the shelf of foam/plywood is the only structure between shelf supports and you are cutting the foam to varying degrees including down to the plywood, I would use 3/4" plywood. Otherwise you may get some sag.
Alternatively, you could build a grid of 1x4's (or even 1x3's). Then you could use much thinner plywood, say 1/4" where there is little cutting into the foam and 1/2" where your riverbed is.
Enjoy
Paul
Mr. B. yeah I can get 2" foam but my trackage will be layered. The main will be at 2", a siding with a few industries at 1" and some more industries at 0. Easier to layer 1" foam than to cut flat level areas in 2" foam.
Which reminds me, there will be a flat section built right on the plywood base. So I guess the question should really be: how thick a plywood for spaning 16"?
I realize that foam by itself is fairly strong but since I'll be cutting in rther deeply I'd preferr some sort of base structure for it. Especially since it will be moved after completion. I'll build it at the workbench then move it to the shelf. Once there it will be there for the foreseeable future.
I have no intentions of cutting through the plywood for any scenic details.
1/2" will span 16" easily as long as you don't stand on it! You know, roof sheathing-which usually spans 16"-24"-is often 3/8" (sometimes 5/16"), depending on local conditions: snow load, wind load and codes, and roofers walk around on it. However, roof panels help support each other around the edges with clips. I would suggest 1/2" spanning your shelf brackets with a 1/2 or 1X2 stiffener at or below the front edge (not supported by brackets). Or-even a Masonite fascia would stiffen that edge.
Dante