plywood module advice needed

[Larry Blanchard]

One of my other hobbies is model railroading. I'm planning to construct a portable HO scale layout with self-contained lighting that I can easily move and possibly take to modeling exhibitions. It would consist of two modules, wach one about 2' deep and 5' long. The best construction scheme I've seen yet for such a module is:

you can see, it's support structure is a series of plywood formers in a C shape. The lower arm of the C is 28", the upper arm is 32", and the upright is also 28". The author of the article used 9mm or roughly 3/8" plywood with the formers about 18" apart. There are several members running the length of the module that add strength and rigidity.

I think it's overbuilt. I've seen similar modules built of nothing more than artists foamboard doubled up for strength. I'm not quite willing to go that far, but would like to use 1/8" birch or maple plywood.

My major sticking point is the 10" radius arc from the upright to the upper horizontal arm. I'd like to reduce that or even eliminate it if feasible. The only weight on the outer end of the horizontal arm would be light fixtures, either under-counter fluorescents or low voltage halogen floods, and possibly a roof which could be foamboard. Somewhere around 2-3 pounds per former or less.

My reason for wanting to eliminate the gusset is to increase the height of a vertical backdrop and make it possible to curve it around the outside end of each module. The original calls for a backdrop curved under the gussets with a 90 degree corner at the ends.

So what do you folks think? Is the curved gusset even necessary? If so, can the radius safely be reduced? There must be some way to calculate the deflection of the upper arm under various loads with various, or no, gusset shapes and sizes.

I've discussed this on a modeling group and one person suggested the radius could be reduced to 6" or a triangular gusset 4" on top and back. Others weren't so sure. So I decided to post here where a lot more of us have built a lot more stuff with plywood.

All help greatly appreciated. Thanks in advance.

[dpb]

On 5/2/2012 4:44 PM, Larry Blanchard wrote: ...

...

I agree 3/8" is way over what's needed; the 1/8" would be fine w/ probably on it's own once it's constrained by the forms. At worst put a thin gusset across the face to add some transverse rigidity.

What I'd probably do is make it more like a tension box--think of the inner form of a hollow door--just cardboard on edge.

The upper radius can be as tight as you wish I think as long as you constrain the leaves in their transverse direction so they don't have the long distance across which to buckle.

Hopefully the thought got thru the fingers to the keyboard to make at least a modicum of sense... :)

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[Lew Hodgett]

------------------------------ NO!!!

Consider painting the gussets to be part of the scenery.

Lew

[Stuart Wheaton]

I Come from a theatre background, and I would guess that the curve has two functions, the structural one is to support the upper arm, and probably can be reduced. The aesthetic function is to let the Backing move seamlessly from wall into sky without an abrupt and obvious transition. If you planned to photograph the trains in this setting, it would be very important for getting a realistic look in the pictures, and will help when people see the layout too.

Stuart

[Larry Blanchard]

True. But that isn't really necessary as there is a fascia on the top front that cuts off the "edge of the sky" if the viewing height is correct.

And the vertical curve makes it difficult (maybe beyond my capabilities) to provide a horizontal curve at the ends of the layout, thus giving the sky a 90 degree corner. And that one can't be hidden from view, so must be disguised - and it's difficult to make such a disguise look natural.

With your theatre background, you'll appreciate this layout:

I could build one that good, I'd start singing "Lord, it's hard to be humble ..." :-).

[Puckdropper]

Larry Blanchard wrote in news:jnu98n$js5$ [e-mail]:

Many curves can be approximated by straight lines. To get the horizontal curve, would it be possible to divide it into several straight sections? The more divisions the smoother the curve, but more divisions require more structure.

Puckdropper

[dpb]

On 5/3/2012 3:48 PM, Puckdropper wrote: ...

I don't think the question was making the curve but simply one reducing the weight by eliminating or at least minimizing the gusset area whether it's round/triangular/whatever...

My thought as outline above is if that is indeed the prime objective it could be done by essentially building a torsion box (laid on its side) instead at quite a bit less overall weight than the plans shown would amount to.

[dpb]

On 5/3/2012 3:57 PM, dpb wrote: ...

Of course, the aesthetics of having the blended corner might be useful and one could retain the curve and still be significantly less in weight as far as that goes...

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