Plywood

There was quite a discussion on this forum around this subject not long ago. Plywood should be fine for your project and be just as strong. The weak points are connections into the end grain. Some use the Kregg tool and others a biscuit joiner. I simply pre-drill the holes and use waterproof glue to hold it all together. 

Thickness..

Plywood is as thick as the tag says. Dimensional lumber has a fair amount of variation depending on the finish, but a 1x  ("one by") is close to 3/4" thick and 1/2" to 3/4" narrower than the label.  2x is 1 1/2 and so forth. basically, you are paying for the sawdust. Here's a useful chart.

Any time you are counting on the thickness of a board, measure it and mark it so you are using the board you measured.

That's softwood of the sort you find at Home Depot. Hardwoods, especially exotics, are another story.

pqe

"Would a 3 inch strip be

How I did it

Hi Doc,

Good thinking I think...  plywood is very stable wrt dimensional lumber.  Since you get a full 48" x 96" of sheet plywood you can get 6 strips of 96" length.  The thing to take into account is the saw kerf.   Your 4" less the kerf will be your new nominal width.  To make the assembly easier waste a little wood and make them all the same width (maybe 3 3/4" or 3 7/8" depends on the thickness of your saw blade).  It's only the last cut piece that would not be easy to match to the others and only one more pass through the table saw.

Good dimensional lumber in the corners to screw into is important too.  2x2 is even better than the 1x1 I suggested in the drawing.  I've used a drill fo the hole and coarse dry wall screws and carpenter's glue to assemble all my bench work.  It was TOMA-like until I installed the track.  Now it's The One Mother Approach......

The only movements I be noticed are a little expansion or contraction when the New England humidity changes.  I use a dehumidifier in the basement and the issue is resolved.

Anyway something to chew on (not my crackers.......)

Good luck and enjoy!

Nick

Brad Nailer

BTW If you don't have a brad nail gun then seriously consider one that will hold 2-1/2" brad nails. I use screws a lot so that members can be relocated if necessary but the basic frame is glued and a nail gun is SO much faster and will not split the wood. You can also put in several along the end or toe nailed like the Kregg tool. Be careful though! 

"If you don't have a brad

     Yeah, the one that's handy for layout framing is the 15 gauge angled finish nailer. As Neil said be careful while learning to use one of these guns, the nails can bend and come out where you don't expect them so keep your fingers well clear of the joints, I clamp them if possible. I've also had nails ricochet off the wood and go flying so wear safety glasses, a nail once bounced off an angled joint and hit my leg and made a bruise. The smaller brad nailers that use thinner brads are nice for nailing roadbed and other thinner materials but are a bit light for benchwork framing.....DaveB

Plywood is more dimensionally stable

 "Where dimensional lumber

In practice we don't orient wood across the grain in our benchwork so the width shrinkage doesn't matter too much.  Wood moisture content typically varies between 6%-14% in a house , using pine framing 3.5 inches wide there could be a maximum change of 1/16 inch so if  we have 3 1/2  box grid framing the elevation of our layout tracks might get 1/16 higher or lower over it's lifetime but all the pieces move together so it's not apparent at the surface( the lineal movement is so small it can be ignored for the usual layout length). Poor design or joinery along with temperature induced changes in rail length are much more likely to cause movement of the magnitude to effect operations. In other words don't worry about the choice of materials worry about how you use them.......DaveB

My experiences with subroadbed/benchwork

I learned about the variability of pure pine lumber the hard way. I built a staging yard about 20 years ago using 1x12 shelving. It was, I reasoned, so much less work than cutting plywood sheets up. Everybody reading this knows what happened next. That winter, the track twisted and distorted greatly. I didn't take any pictures but it looked like some of the twisted or buckling railroad track videos you can find on YouTube.

In another area, I had a long section of double track mainline that I laid on top of particle board shelving. I had already learned that pine was no good and figured that something with a high glue/binder content of some sort would be much more stable.It went shproing, too, when the weather here in Chicago went down to -18 F. In both this case and the above case, I was sure to leave some gaps between rail ends at the joiners. Not enough, obviously.

I had also laid my major classification yard around the same time. For some reason, I chose to use decent quality plywood for that. There has never been a problem with that yard.

Finally, in yet another area where I wanted flowing, graceful curves in a more rural area. So, I tried my hand at doing a spline subroadbed with pine lath strips (1/4" x 1 1/8"). That has proven to be very stable as well.

Fortunately, I became very busy at work and couldn't do any more bad engineering. I am only now getting back to working on the layout. In fact, I just recently ripped up that pine shelf staging and am finishing putting down the plywood replacement. This will eventually be a [relatively] hidden staging yard so I will be sure to go through at least one winter to check out the dimensional stability.

Using shelving product was a blatant attempt on my part to save time and effort over doing it right. As the old project management maxim goes: "Take the time it takes and it takes less time."

Vince

Speed warp...

Pine shelving behaves just like the basswood in our model structures. Get it wet, and it warps. The cure is the same-- paint or varnish it to keep moisture constant. However, there is pine and there is pine. The cheap stuff (green) is cut, shipped, and sold as fast as the traffic allows. Wide boards will have some heartwood and a lot of sapwood with widely different moisture content. As they dry out on your layout, they will develop a curl. Better (construction) grades are dried in the sun or in kilns until the moisture content matches the relative humidity. After that, changes in climate will have minor effects. Apply moisture to one side though (or paint just one side), and you will get funny shapes again. The very best (furniture) grade is dried in large slabs, then cut to size and planed. That stuff is stable.

Low density particle board is essentially a sponge. MDF is water resistant, but heavier and often more expensive than plywood. When I actually want to build a shelf or a utilitarian cabinet, I use redishelf, which is a prefinished MDF product.

What I used to build for a living. The electronics racks are made of redishelf.

pqe

Redishelf.

Pelsae is on track as usual.  The other thing I liked about it is it was finished on four sides until I cut it in half.

You can see it on the lower left.  The book shelves bought me the upper level....   I finished the rough cut edge with Dunham's Water Putty and painted some.  On others I used iron on edging.  It was a coin toss on time for edge finishing.  I didn't want to buy another flat iron was the reason to change to the Putty. You can also see on the right some of the bench work system I've used.  I happened to have 3/4" plywood for the ends and 3/8" for the cross pieces.  The depth here is about 16".

Nick

Very Nice!

I am going to steal that backdrop/dust cover idea for my 4x6.  Thanks for sharing.  

Dimensional Lumber vs Plywood

I have used both in the construction of my current layout.  I personally prefer to use cabinet grade plywood (3/4" which is actually around 23/32" - yes even that thickness on an N-Scale layout) and the better grade of dimensional lumber (I think that it is called white wood at Home Depot - and it has to be straight as an arrow and without knots). Yes it was more expensive but you get what you pay for in either dimensional lumber or plywood, i.e., if you buy the cheap stuff in either then you get poor performance.

Based on all the comments

Based on all the comments above, I came up with this design for a 2x8x48in section (height includes adjusters). Clear span about 51 inches which is perfect for movable shelving.  Legs will be bolted to side rails and cross rails.  Wood surfaces will be "sealed" with Kilz or equivalent primer.
Light tan = 23/32 plywood (7 ply) 1x31/2in siderails, top and legs.
Brown = 1x4 (or 1x6) #2 pine or poplar for legs, end rails, interior cross rails.
Green - 1x2 ripped from larger pieces. 

MDF is water resistant, but

MDF (Medium Density Fiber core) is no more resistant to water than is particle board (or flake board).  Get either of them wet and they'll both swell up like a sponge.

MDF is normally cheaper than most plywood, unless you're comparing it to exterior grade CDX.

I wouldn't use any type of MDF for the frame construction due to the weight, not to mention the poor ability to accept nails or screw as it tends to split very easily, even using pocket screws.  But I have used a piece of 1/4" to lay on top of the framework to stabilize the frame and then laid and glued a sheet of foam on top of the MDF.