I’m getting ready to start building my HO layout and need advice on the thickness of the plywood that would be practical for my layout.
The layout will be a cookie cutter type with L girder benchwork. All along I have planned to use 1/2 inch plywood for the sub roadbed. But now that the time is here I’m questioning whether or not I should use 3/4 inch?
The layout will be in an E shape 15’ X 20’. It will have a lower level for staging. To get to the lower level the trains will run around a double track that will be attached to 6" wide plywood. It is this plywood that I’m in question of.
I know the experts here have already gone through this dilemma and have reasons for using one over the other. Please chime in and let me know your reasons for either.
I have used both, the choice being what I had on hand, or what I could scavange. When I have to buy it, I use 1/2 because it is easier to cut and work with. Both are strong enough for HO and spans up to 2 feet.
If the risers under the descending tracks are 12 inches apart 1/2 inch ply would probably suffice. Rather than use cork roadbed, I plan to use sheet cork in double track width and glued to the plywood. It won’t be ballasted so it should be very quiet. Defiitely, don’t lay the track right on the plywood.
In my last layout with L-girder and 16 inch spaced girders, I used half inch ply, BUT I glued 1 x 2 (actualy 3/4 x 1 1/2) wood beams under the center of each span with elmer’s glue. I used adjustable C clamps to hold them firm whuile the glue set. No sag whatever. I had plenty of scrap wood left from the bench work construction so it was free.
Even 1/2" is unecessarily thick with HO and smaller scales.
You could get by with 3/8" of a quality brand and 15" spans with no difficulty. The thicker it is, the more plwood costs and the heavier it is. It also costs more to cover and to cut, and takes more energy, to boot.
I firmly believe that if your benchwork is constructed well and with good material, your roadbed of cookie-cutter style need not be as thick as 1/2" unless you find you must span between risers that are perhaps 24" or more.
The answer is in the distance between the cross members of the L-girder. 1/2" should easily support a 6" wide strip for distances up to 20" or so. I would cut a strip and test it out. See how much flex there is versus how much flex you want it to have.
Our club has a minimum sub-roadbed width of 4" and we therefore require 3/4". The maxium span is 20". That is probably over engineered, but we assume eventually, for some reason, people (and big people at that) will be leaning on the track.
Another thing to keep in mind when selecting your ply for cookie cutter approach, is, even a quality 5 ply in 1/2" may not be strong enough for turns. Any plywood is strongest when ripped with the grain, as you cut it for a radius, especially smaller 18-22", the risers for support should be much closer for stability. I would not recommend that you allow any ply to have surface graining pass the 45 degree (1/4 of the turn). If you feel that many splices throughout the turn are not stable enough, you can laminate the subroadbed and alternate the seams. In this method 2 layers of 3/8 is very strong. Many when building helixes do so w/ great success.
There is no “grain” to plywood. Plywood is made of layers of thin wood that has been peeled off a log and laminated with alternating layers perpendicular to each other. That all said, I agree that 1/2" is sufficient up to 24" support centers,
Ivenhen, Thanks for picking up on the “graining”. In lay terms this is the only way to describe the strength factored into the ply. Of coarse ply has no grain, but is strongest when the orientation of the outer plys are not crosscut. As you mention the interior plys may have voids also showing that the outer plys(even though plugged or boat patched) will afford the most strength.
I can’t agree more about the poor quality of the ply whether pine or fir at HD and Lowes. A quality lumber supplier will have a better product and generally is very little more in price, than the so called “premium” varieties from a home center.
I would almost always reccomnend using stronger materials. The last thing you want to do is complete construction, have difficulties, and then kick yourself for cutting corners. I think that 1/2" should suffice but the additional strength and stability may be worth the cost. I have used 1/2" extensively on shelving in my garage and not had any sagging problems with boxes in excess of 100 lbf. The maximum span that I you is about 18".
As far as the span goes, all plywood is grade stamped. One of the things on the grade stamp is the span ratings. There are two ratings, for vertical & horizontal application. Google US Plywoos Assoc, they will have illustrations of the stamp & show where the ratings are. Don’t ask anyone at HD, 84 Lumber, or Lowes about it - I’m the only one in the HD I work in that could show & explain the stamp! These ratings are made to rate the roof snow load etc or side wall wind (hurricane) ratings. Your local lumberyard will carry the better grades & have someone there to explain the span ratings.[8D]
Actually, there IS a grain to plywood - a double grain (it goes two directions). In five-ply plywood, generally three run lengthwise with the panel and two run width-wise.
Structurally, the weakest direction in five-ply plywood is around 55 degrees off the top and bottom layer grain direction (that’s the 3-ply grain. In seven ply sheets, the weakest direction is about 51 degrees off the top grain direction). The sheet will flex easier along that line than in any other direction. It isn’t enough to make a major impact on subroadbed, however…
If you go with 1/2" plywood, make sure it’s 5-ply, not the cheaper 3-ply. More layers glued together means smoother holes drilled (for turnout motors, etc). Stronger & less prone to warping.
Luckily there are several lumber yards near here other than Home Depot, Lowes and 84 Lumber. I’ll check them out this weekend to see what their prices and inventory looks like.
The better grades of plywood help, but 24 inch supports are iffy for half inch ply, 12 inch is good, 16 inches is not as good as twelve. Better 5/8 ths, and make sure the board is not warped, they don’t get straighter with time. Do use the 5 ply, it is much better to work with. And use fresh, sharp, fine tooth saw blades.
I don’t see how you can say this. If you support 3/8" plywood that is in a strip 3" wide between two risers set 24" apart and place an HO Challenger so that its couplers are equidistant from the riser centres, you will get something like 1/32" deflection downward. This heavy engine will deflect the centre of the span so little because of its overall weight distribution, much of which is within 6-8" of the risers. That is where there is most resistance to bending, within 6" of either side of the risers. So, saying that 1/2" 5-ply should not occupy spans greater than 24" is overkill.
In the case of a smaller engine, say a light Mikado, the deflection will be much the same for all the obvious reasons. Now add all the scenery, the strips and tape or paper, the plaster, or the glued foam, and fix it to the plywood. Your roadbed will be now supported to the extent that you will get effectively zero (0) flex over such spans.
I’ve used 3/8" ply with 24 inch risers and it warped and sagged. Now, a better grade may have helped…some. I simply don’t think it is worth it to use anything less than 5 ply 1/2 inch board, better 5/8 inch if you would have any 24 inch spans. The three ply board tends to be soft and subject to deflection and twisting.
You are going to get many different answers to your question based upon the personal experiences of the many modelers answering your question. And most of the info will be correct from what they are doing.
Plywood is very strong, stronger than boards of the same thickness, that as why they use laminated beams in home construction that eliminate the use of support columns in the basements or large rooms on any level of the homes.
So the questions is, what do I need? The shorter the width from the wall, ie 12" vs 30", the thinner the plywood you can use within reason. If you had a 12" width, 1/2" plywood would perform very well. At 30", 1/2" will perform well “if” you place supports undernieth at appropriate spacings, not so much for breakage strength, but for elimination of sagging under weight, or, moisture causing swelling or shrinkage when too dry.
Many people will tell you that 3/4" or even 5/8" is overkill. Are they wrong? No. But if money were not an issue, or, I had 3/4 or 5/8" hanging around from other home projects, you bet I would use it? Why? Because I “know” I would never have a problem with that thickness unless my location was prone to a heck of lot of moisture, and I mean a lot!!
It is all common sense, the thicker the plywood, the stronger the base, the less problems that you could have. Probability of a problem is whole different ballgame, and you can cut those odds by using more supports on thinner plywood.