Subroadbed Thickness Recommendation, Please

[Anonymous]

Guys,

My first layout was a tabletop using 3/4 inch plywood stiffened with 2x4 along the edges. Now I have finished the L-girder benchwork for a portion of my next layout. I can't locate my copy of Linn Wescott's book on constructing benchwork. I intend to build the subroadbed by laminating two thicknesses of plywood and use cork roadbed on top for the track (This is an HO scale layout in case that matters). What thickness of plywood should I use and is there a maximum spacing recommendation for the risers that support the subroadbed? I also intend to build the roadbed three inches wide for single track portions and five inches wide for double track portions. Does anyone think this would be a mistake? Thanks in advance for your assistence. - Ed

[ndbprr]

This topic will be getting lots of opinions and probably little in the way of engineering support! I use 1/2" plywood on 1 x4 frames 36" wide with one support every two feet with no sagging problems. I am currently debating switching to MDF (see my start of a topic about MDF) as it is extremely smooth and deadens sound. Given my druthers I would go 3/4" over 1/2 plywood next time as it is definitley overkill and you can park Boswer PRR steamers near each other. A lamination of two sheets of 1/4" plywood using contact cement is probably going to be stronger than one sheet of 1/2" plywood as it will have more layers. There are lots of right ways and wrong ways to do anything. The foam guys will probably weigh in with why foam is superior with guidelines fo support

[Sperandeo]

Hi Ed,

I'm using 3/4" plywood for subgrade (subroadbed) in widths similar to those you have in mind, and I'm very happy with it. I guess I don't see the point of laminating plywood – it's already laminated – unless you want something thicker than 3/4". I've only noticed one sag, where I had a long span between risers around a curve. I fixed that by screwing on a length of 3/4" square stock from underneath.

Thanks for signing your name.

So long,

Andy

[nfmisso]

Hi Ed;

I concur with Andy, though I do have a reason for laminating: the weight of a single sheet of 3/4" plywood usually means you need to people to move it around with any precision.

For example, I have no trouble picking and carrying a 3/4" piece of plywood, but I would not try to do that in the house because the combination of weight and size makes it a bit unstable. On the other hand, I would have no qualms with 3/8" 4 x 8 sheets.

If you really want to laminate, use 3/8" thick sheets. You could cut out the lower one precisely, then cut the upper on a bit larger, and go back with a router to make it the same as the first one.

If carrying, or something similar is not an issue, stick with the straight 3/4"; it will be a lot less work.

From an Engineering perspective, there is not a significant difference between 3/4" and laminated 3/8" thick pieces if the adhesive for laminating is as stiff and strong as the plywood adhesive. I am a Professional Engineer, and am qualified to make this statement.

[Anonymous]

Nigel,

Thanks for your opinion. I am also a registered professional engineer so I guess I am qualified to read your advice.[;)]

Andy,

Thanks for your opinion. Anyone would be ill-advised to ignore your experience.

Other fellow,

Thanks for your opinion, too.

I am going to laminate the subroadbed to help improve the joints. By laminating the subroadbed, I can stagger the pieces creating a lap joint. If anyone has tried this and concluded it was more work than necessary, I would like to know that. But since this is the first section of the new layout, if I learn it the hard way I can do something else on the next portion.