Foam with minimal support for layout?

[nickelplate759]

Apparently layout construction questions go here, so...

My last layout had a base of 2" blue foam glued over 1/4" plywood over a 1x3 frame.  That worked, but it was hard to level the roadbed.    I'm thinking of ditching the 1/4 plywood, and using the blue foam as self-supporting over the frame.  That way I can do the cookie-cutter thing for gentle grades if I want, but more importantly can easily shim up the foam where I need to to level it, or even punch completely through the foam if I want a riser for an upper level or scenery support.

How close together must the 1x3 supports be under the foam - in other words, what's the longest unsupported span of 2" blue foam I should plan for?

George

[loyalton]

More info, please. Is the new layout going to be 4x8? If not, a diagram would be useful or give us the dimensions of various sections.

I have to admit to being confused about your original problem about leveling the roadbed. Was this because of the plywood, the foam (both usually dead flat) or what I suspect, using 1x3s for the frame? Many have a preference for a plywood frame for stability, glued and screwed with cleats/gussets; 1/2" would stand up easily for home use, cut at least 4" high. You could maybe recycle that 1/4" stuff.

Add a 1/2"-1" lip around the frame and the foam can go otherwise unsupported on a 4x8, assuming no yard full of brass engines and no plaster mountains. However, I don't think this would work going cookie-cutter style; 2" foam isn't going to bend well for transitions. It would be simpler to pile up pieces of 1" foam on top for an upper level and cut transitions.

You will probably still need crossbars if you use switch machines or linkages. They might help out if you have a lot of wiring. Preplan their locations.

Also, a warning that foam without a base can be like running on a drum head, fairly noisy.

[davefoxx]

Actually, 2" foam DOES cookie cutter well.  I did just that in an experiment on my HCD layout, and it was a complete success.  Here's a post from a few years ago:

I flipped the 2" foam upside down on the table and glued on progressively larger foam blocks.  Luckily, I have a low temperature hot-glue gun that works great on foam.  Starting at 0" and increasing in 1/8" increments, the incline rises two full inches in approximately 75" of run.  The siding halfway up the hill is at 1-1/4" and will be level.



Then, I flipped the foam back over, and the result made it go from this . . .


to this!


Perfect!  The foam has just enough flex that this worked beautifully.

To answer your question regarding unsupported foam, if I were to build over a frame, I would go no more than 16" apart, which is probably overkill.

Hope this helps,
DFF

[nickelplate759]

As you guessed, it's the frame that isn't perfectly flat. Absent tools like a table saw, etc., I can come close but it's not perfect.
I did use ripped plywood for the frame last time, so the boards were straight at least.  However, the spans are long enough that there is some (slight) vertical deflection, and my woodworking is rough enough that there are some minor deviations from flatness.  I live in a condo building, so I can only build in my parking space or in the layout area itself.

The layout (N-scale is around-the walls in an 9x10 space.). Here's an outline, with rectangles to show the major frame structures.

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George

[Ed Kapuscinski]

Alright brother, let me tell you...

I've had lots of experience with foam, including building a multi-part shelf layout entirely of it and shelf brackets (no benchwork at all): http://conrail1285.com/tag/ncr-shelf-layout/

Here's what I've learned. Foam is great stuff. Incredibly useful and dimensionally stable. Under "normal" layout conditions, it works perfectly.

But there are drawbacks (some of which you're avoiding by having some benchwork). The biggest one is that you cannot easily attach things to it. You can't easily screw to it (it's possible, there's a recent thread about it), and you can't nail things to it. This makes things like hanging wiring, attaching turnout controls, and importantly (to my shelf layout), attaching one piece to another. It was very difficult to keep the pieces aligned.

Now, on my current layout, I'm building it all out of 48"x18" boxes. I've attached 1" foam to the top, and it seems fine. I still have issues with attaching things, but I'm working around them (thanks @rodsup9000 and @Lemosteam). I don't see any sag at all in the middle.

Remember how I said under "normal" conditions? The one place foam gets tricky is during construction. When I need to lean into my friend's layout to ballast the far back corner, I can put my hand on it and lean. If it's foam? I might think twice. You just have to be a little gentler with it.

I would definitely recommend some cross pieces in your plan above, if for no other reason than to keep everything squared up, and to give you additional places to attach things (like DCC components). It's also important because, in case you need to use multiple sheets, you want to make sure you have something to fasten their edges to. I'd say maybe every 36". That should be more than enough. Oh, also, when putting in cross pieces, do yourself a favor and cut a couple Vs out of the top edge so you can easily run wires.

[nickelplate759]

Thanks Ed.  The crux of my question is - how close together should I put the cross pieces?  I was thinking every 18" or less.
 I just drill 1/2" holes through the cross pieces to run wires, on the theory that it's stronger than notching the edge, but I suspect that given the the likely stresses the layout should encounter it doesn't actually matter .

George

[Lemosteam]

@Ed Kapuscinski and I had a go-round on this on the a-forum some years ago when he first started his original foam shelf layout.

Remember, the foam we use for our layouts was engineered to be installed on a vertical surface, not horizontal so there is no concern about sag or deflection between studs.

Because we use it horizontally, these concerns become reality in several ways, gravitational sag, and deflection under load.

Gravitational sag can be mitigated with enough structure, maybe 16" square max for 2" foam.

BUT, as Ed correctly mentions, a misplaced hand in the center of that 16" square may prove disastrous. Will it support a railroad? Yes. Will it support 1/4 the weight of your body? Do you want to risk it?

At minimum, a lauan base over the structure would support that load.

Just my two cents.

[tom mann]

I think if you want to go light weight, a 1x2" frame with 1" foam on top is the way to go.  If a lot of landscape needs to go under the track, use 2" foam on top cut cookie-cutter style and place the track on that.

[Mike C]

I'm on my 3rd foam layout . None of which have had traditional supports . The first 2 were supported in 4 areas spaced somewhat equal distant from the corners and center . It worked fine and had no sag with 2" foam . My currant is supported bu 2 L girders made out of 1x2 lumber that run the length of the layout . Layout is 8' long . It's been set up for almost 3 years , and I haven't seen any sag problems . With cross braces every 16-24 inches I think you'll be fine .

[Ed Kapuscinski]

Thanks Ed.  The crux of my question is - how close together should I put the cross pieces?  I was thinking every 18" or less.
 I just drill 1/2" holes through the cross pieces to run wires, on the theory that it's stronger than notching the edge, but I suspect that given the the likely stresses the layout should encounter it doesn't actually matter .

George

Like I said, I use an 18"x48" grid under it, so I'd say 18" should be fine.

[Brian M]

With regards to being able to mount something on the underside of a foam layout, I've had success gluing a piece of 1/4" plywood or hardboard to the foam.  Then you have a stable mounting location for something like a switch machine, a spot to secure wires, etc.  To hold it in place while the glue dries, I've either tacked the hardboard up with nails pushed into the foam or wedged in a piece of 1x2 cut to length (1x2 sits on the floor, shimmed up to compress the hardboard against the foam).

And of course one can always add additional cross member supports if there is a concern with the foam being able to support weight.  A 1x2 cross member is generally more than sufficient to remove the risk of the foam breaking under the weight of leaning on the layout.  The number and location of cross members depends on the thickness of foam you're using and the span needing support.

-Brian.

[robert3985]

My experience with "foam only" as layout benchwork has not been good.  It doesn't take a lot of deflection (sag) to really screw up all that trackwork you worked so long and hard to put down, under all that scenic material you took the time to accumulate and so precisely and lovingly applied in a realistic manner.

Since benchwork is the FOUNDATION of your layout, upon which everything is attached, it should be STABLE, and extruded Polystyrene is not designed to be stable...it's designed to be insulation, and hang on walls and garage doors.

IF (and it's a big "if") I really felt a need to build a layout's benchwork out of extruded Styrofoam, I would use Kato Unitrack for my trackwork, which is much stiffer vertically than any code 55 flex on cork.  However, then I would be sacrificing prototypical appearance and layout design flexibility just for vertical strength.  I'm not willing to do that under any circumstances. I shouldn't have to compromise my track standards just because I'm building on an unstable foundation.

I construct my modular/sectional layout out of premium pine L-griders tied together with plywood gusseting, glued and screwed together on a perfectly flat surface.  Subroadbed is constructed of 1" tall strips of 1/8" Masonite glued together into a spline and mounted to my wooden benchwork with pine risers.  Cities, yards and large industrial areas are made with 1/2" CDX plywood, held in place with pine risers too. 

I glue Midwest Cork Products N-scale cork roadbed to the splined Masonite subroadbed, then sand it so it's flat.  To this, I mount Micro Engineering C55 flex, and C40 flex, hand-laying all of my turnouts and also branchline C40 track.

Then, everything gets wired with 22AWG feeders to each and every piece of rail on the modules and layout sections, and my DCC wiring goes in.  It's VERY EASY to work on both trackwork and wiring before any scenery base has been installed with very little crawling around underneath since at this point, there isn't much "underneath".

After the track has been tested and run and the electrical and mechanical problems have been corrected and re-tested, THEN...I start laying in 2" thick extruded insulation as the scenery base, and build my scenery contours relatively precisely by layering it and carving it, filling cracks and voids with Sculptamold.

This, IMO is where extruded Styrofoam really shines...as a scenery base, with very little if any structural responsibilities relative to supporting trains running or supporting the layout.

Some of my layout sections are over 20 years old, with complex trackage constructed from C55 and C40 rails, each section being 6 feet long with no joiner tracks...and I don't have any problems with trackage kinking or not aligning whatsoever.   

However, on four all-extruded foam layout sections I made less than ten years ago from 2" blue Styrofoam, with as many as five layers glued together, I had so many problems with track popping, pieces falling off, denting and the structure amplifying the sound of the trains that they have all been replaced with wooden L-girder benchwork constructed sections...which work.

If I were you, and I didn't have access to woodworking tools or a shop, I would consider using hollow core doors as your layout benchwork base...which work great as a support for Styrofoam and as a strong structure for mounting legs and gusseting to tie the layout together.  Legs with carriage bolts screwed into T-nuts makes keeping your layout level easy.

Cheerio!
Bob Gilmore

[nickelplate759]

The doors are an interesting idea, given that much of my frame is 24" wide.    I'd need a 96" door, a 75" door and a 90" door.  Can they be cut down without compromising their strength?  80" and 96" are common heights.  I don't think anyone makes a 75" door...

I'd also need to figure out how to support the wider area shown in the lower-right and upper-left portions of the drawing.

George

[Ed Kapuscinski]

Can they be cut down without compromising their strength?  80" and 96" are common heights.  I don't think anyone makes a 75" door...

Yep. But, what you'll find is that the cut side now has a hollow edge (hence the "hollow core" part of their name). That's easy enough to fix though, by simply adding in some dimensional lumber to provide the frame member that is now missing.
http://www.tomcomknowshow.com/how-to-resize-an-interior-composite-hollow-core-door.html

[Iain]

I've flirted with the idea of foam with an aluminum benchwork.  It should be reasonably strong, but also lightweight.