Tell the truth, your troll alarms just went off.
I've secretly believed that to be true even though there have been many posts stating that you don't need any plywood under 2" of foam. I hedged and used the plywood I had on hand, which happened to be the thinnest plywood you can buy in a big box store--3/16" unless it really is 1/8" I figured that would be good enough to screw a tortoise machine. Probably true, but I decided to use ground throws.
The good news is I have a bored friend who voluteered to build a truss style bridge. The bad news is I have to dig a hole through much of the thickness of the foam and probably 1/2 way across a 24" piece of foam. The bridge piers are going to be sitting on or near a thin piece of luan plywood. So much for the intrinsic stability of foam.
I could glue a piece of thicker plywood beneath the luan. I could add additional joists at the piers or I could create a drop down section with thicker plywood. Does anyone have any other ideas?
Knowing what I know now, I would have gone the Ken Patterson route with 2 or 3 layers of 2" foam, giving me tons of space for negative landscaping.
Henry
COB Potomac & Northern
Shenandoah Valley
BigDaddy Tell the truth, your troll alarms just went off. I've secretly believed that to be true even though there have been many posts stating that you don't need any plywood under 2" of foam. I hedged and used the plywood I had on hand, which happened to be the thinnest plywood you can buy in a big box store--3/16" unless it really is 1/8" I figured that would be good enough to screw a tortoise machine. Probably true, but I decided to use ground throws. The good news is I have a bored friend who voluteered to build a truss style bridge. The bad news is I have to dig a hole through much of the thickness of the foam and probably 1/2 way across a 24" piece of foam. The bridge piers are going to be sitting on or near a thin piece of luan plywood. So much for the intrinsic stability of foam. I could glue a piece of thicker plywood beneath the luan. I could add additional joists at the piers or I could create a drop down section with thicker plywood. Does anyone have any other ideas? Knowing what I know now, I would have gone the Ken Patterson route with 2 or 3 layers of 2" foam, giving me tons of space for negative landscaping.
And this is why open grid benchwork remains one of the best methods of construction.
OK, I can maybe see foam as a light weight support for various plaster lanscape methods, but as a total bench work, even over plywood, no thank you.
I want benchwork I can lean my 200 plus lbs of body weight onto......
And now I'm sure I will be told why I am wrong and how great foam is........
Sheldon
Maybe I'm not picturing this right, Henry, but do your think that if the piers are sitting on the luan, the first train is going to collapse everything, and train, bridge and all is going down?
I don't think you'll have anything to worry about.
Do you have room the put a second piece of luan, grain running opposite of whats there, in the "river bed", to set the piers on ? or at least just under the piers?, and adjust the depth of the river accordingly?
I don't know what type of frame work the luan is sitting on, but under where the bridge is going, can you add another joist, that runs perpendicular to the main joist? (hard to describe this).
Mike.
My You Tube
mabey just a piece of 1x4 glued to the bottom beetween the joists and screw it to the existing joists
STEVE
mbinsewiMaybe I'm not picturing this right, Henry, but do your think that if the piers are sitting on the luan, the first train is going to collapse everything, and train, bridge and all is going down?.
I used this article and modified it with a thin piece of plywood and 2" of foam 2' x 5'
http://mrr.trains.com/how-to/get-started/2011/11/benchwork-for-your-model-railroad
The bridge has to bridge something, which means I will be taking 'V' or 'U' right out of most of the foam. 1" is going to look too shallow so I will have to go deeper.
The benchwork, is just benchwork at this point, no track. I can support with a joist parallel and underneath the bridge as you suggest, or perpendicular at the ends of the bridge, or add plywood underneath.
I wanted to add grade to this section anyway. As Sheldon points out, easier done with his style of benchwork. But now that I think of it, I could add 2" of foam, shorten the legs 1" and contour the foam to a 2-2.5% grade down to meet the other module.
rrebellSo you did it wrong. You just glue another peice of foam to the existing foam where you cut, works like a charm.
No foam has been harmed yet in this discussion. I'm playing the Allen Greenspan card.
“ I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant”
If you mean I should fill up the river bed with a piece of foam and put a bridge on top the now flat pieces of foam, that is probably one example of when "there is a prototype of everything" is not true
BigDaddy I could create a drop down section with thicker plywood.
This is what I would do. It will give you the most freedom to create what you need without pulling any punches.
Chip
Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.
Cut through the whole thing - luan as well. Glue a piece of 2" foam to the bottom.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
This thread is a good example of why we have engineers. It's not that any material does "x" it's that a material is used in accordance with proper design practices that make use of the material's strangths.
Of course foam will fail if it's installed so that it's benefits are degraded. Cut out most of a 2" thick iece of foam and, guess what, it's going to be weaker. That's the reason why Ken P. chose to ADD foam in the situation described.
Even steel and concrete can end up too weak to stand. Look at the recent pedestrian bridge collapse in Florida before it achived full design strength.
Mike Lehman
Urbana, IL
In fact way back when, before my previous layout, I was going to do a small switching layout, which is all I had room for. One of the things I wanted to have was a coal yard, which would require cutting well in to the foam layer - so I built the first module with 2 layers of 2" foam. When I moved and had the whole room, and changed the layout, I didn't need that, but since I had the first module already built that way, I just built them all with 2 layers of foam rather than scrap the one I had built and start over.
No one has ever claimed that 1/2 inch of foam is going to suffice as benchwork and subroadbed for a layout. 2 inches of foam is fine to bridge several feet between benchwork joists. As Sheldon pointed out, even that will not support the weight of a fully-grown craft beer afficionado like me, either.
This is how to use 2-inch foam without a problem:
This is a liftoff section, about 2 1/2 feet long. The base is a piece of 2-inch foam. It's surrounded with hardboard, but that's for protection and appearance and adds no structural strength. To get the stream bed beneath the bridge, I built up the banks to maintain the full strength of the 2-inch foam. If I had cut out most of the foam instead, I would have lost the strength.
It takes an iron man to play with a toy iron horse.
BigDaddy rrebell So you did it wrong. You just glue another peice of foam to the existing foam where you cut, works like a charm. No foam has been harmed yet in this discussion. I'm playing the Allen Greenspan card. “ I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant” If you mean I should fill up the river bed with a piece of foam and put a bridge on top the now flat pieces of foam, that is probably one example of when "there is a prototype of everything" is not true
rrebell So you did it wrong. You just glue another peice of foam to the existing foam where you cut, works like a charm.
For my original design, 2" of foam was perfectly adequate. Using traditional benchwork with risers gets one thinking of elevations right away. Starting with a yard and foam makes it easy to think of one thing.....flat.
I've been staring at this second module for months, rearranging it from straight to L and back again. The plan was to gain some elevation, add a tunnel and maybe an ice house or grain elevator, not to have a turntable and a bridge. That was going to be the 3 and 4 sections. Plans change.
I do wish I would have given more thought to elevation in the beginning though or it will be section 6 or 7 before I figure out how to get enough elevation to get one track to cross above another.
rrbell I get the wrong end of the stick a lot.
Another note. You can add more strength to the glued foam with peices of bamboo skewers (or other things) put through at an angle.
Note to self, a 4x8 sheet of 2" foam does not fit into a Toyota Highlander unless it is cut in half or it is an autonomous vehicle.
BigDaddyIf you mean I should fill up the river bed with a piece of foam and put a bridge on top the now flat pieces of foam, that is probably one example of when "there is a prototype of everything" is not true
Pour chemicals on and set it on fire and you've modeled the Cuyahoga pretty prototypically...
One of the Canadian wooden bridges burned two years ago. I don't model tragedies, fires, accidents, but it's a striking video.
The system doesn't want me to post a Youtube video. Follow the link you can see it full screen https://youtu.be/0UX9Y0X-9PI
I meant the foam river, not the bridge.