Track or Subroadbed, ...Expansion\Contraction problems


B

beiland

Well-Known Member
What exactly is the problem that almost all us face with our model railroad track seeming to change shape (length in particular), with temp & humidity variations? Can it be attributed to the track alone, or the subroadbed alone? ...or primarily to __?

I've heard a number of folks who say the expansion/contraction of our rail itself is minuscule compared to that of the wood that most of our subroadbeds are constructed of. And that is the primary reason we experience what appears to be a change in track length, but its really the roadbed the track is attached to??
 
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I would think you could eliminate a lot of the expansion/contraction issue by giving your sub-roadbed a couple of good coats of primer to seal it . this is my plan anyway since I'm in a basement, and summers in Illinois can be fairly humid.
 
You always need to pause a year or so after you've established your benchwork. Let the wood have its way and settle in. After a couple years the wood should be settled down and you can install your scenery. You can lay your track in the meantime, but ya have to make adjustments as the wood under it expands and contracts. Just a little trimming here and there, but once it's done you can get on with the rest of your work. The bigger your empire, the more the expansion. I had times of wood contracting that I had to take almost an inch out of some track.
 
So Ken, you are saying that almost all of the problems are associated with the wood understructure (subroadbed & benchwork), not the track,...correct.

Migalyto,...Yes I definitely plan on painting (sealing) my plywood decks.
 
Very little dimensional lumber is properly cured/dried these days.
You will have way less problems with warping, twisting, and moisture if you use plywood for all legs, cross braces, and framework ... choose a wood other than pine for the top. There is some 7/16 Chinese stuff at a local hdw here that is good enough to build cabinets with, and another (I forget) from South America that is just as good.
Make the legs by screwing & gluing 2 pieces together, or make them "T" like.
If you don't plan to walk on the tabletop and are going to use a plywood top - make the framework from 1x3 pieces. Most layouts are way overbuilt.
 
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I agree that the rail has little to do with expansion and contraction issues. It's the wood used in the sub-roadbed that is the problem. Wood can absorb tremendous amounts of moisture and will expand or when drying out contract.

When using lumber for framing bench work the lumber should be acclimated to the area it will be used for several weeks before the starting the workbench construction. Allow the wood to get used to its surroundings. Basement areas should have dehumidification during summer months to maintain some constant level of humidity throughout the year.

When I constructed my bench work I made sure that whenever I joined two pieces of 1/2 inch plywood sub-roadbed the joints have a reinforcing plate of 1/2 plywood under the joint and all the boards glued and screwed where attached to maintain a secure fit. In fact one area where a joint was necessary i used two plates to securely fasten together to the sub-roadbed.

I recommend using only quality plywood and not any other type of manufactured sheet goods. When purchasing framing limber for the bench work, check to make sure its straight and not all ready warped in the store of lumber yard.

Lastly, be generous in the amount of raisers you use if the sub-roadbed is elevated up from the bench work. I recommend using only quality plywood and not any other type of manufactured sheet goods. Don't hold back in the number of screws you use to fasten the raiser(s) to the bench work. Minimum of three screws and stagger the screws to provide extra stability. I like to attach a piece of 1/2 at horizontally at the top of each riser to have another spot to secure the sub-roadbed to the riser as well as installing screws into the riser itself. This piece of support is also glued to the riser and screwed.

I recommend using only quality plywood and not any other type of manufactured sheet goods. When purchasing framing limber for the bench work, check to make sure its straight and not all ready warped in the store of lumber.

Build strong bench work and expansion and contraction shouldn't be an issue.

Greg
 
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One of the primary reasons I posed this question was to determine the pluses and minuses of how much gap to leave between the rails themselves,...is it really necessary, and if so how much??

Generally I've heard a number of folks that have said it is not necessary if the subroadbed material is proper, both in selection and acclimatized.

I have purchased a real good quality plywood, and it is presently presented to the climate, and it will be sealed with paint on both sides prior to use. I am also utilizing steel framing.

So I do NOT anticipate any problems with benchwork distortion. Just was wondering about gaps in the rails themselves.
 
While expansion/contraction in rails is minimal, there is some. In my climate, if I lay track in the summer, I generally butt the rails together. If I am doing it in cooler temperatures of winter, I leave a small gap, the thickness of a standard business card between adjoining rails. Fortunately I do not have major changes in humidity, so wood is not really an issue like it can be in basements. Maintaining a constant humidity, whether it be high or low is the key here. Acclimating the wood as Greg and Ken have posted also helps greatly. My experience only.

Willie
 
santafewillie said:
While expansion/contraction in rails is minimal, there is some. In my climate, if I lay track in the summer, I generally butt the rails together. If I am doing it in cooler temperatures of winter, I leave a small gap, the thickness of a standard business card between adjoining rails.
Willie
Click to expand...
Yes I thought that was a good idea also.
 
How Plans can Evolve

Funny how things sort of evolve.

In the beginning I was seriously considering 2" foam subroadbed shelves held up with some pretty nice metal brackets from Home Depot. The 2" foam is not so readily availble here in FL, so I looked around for options.

Found what I thought was some decent plywood (called Blondwood) at Lowes. I monitored a stack of it at their store and i became less impressed,...and thought perhaps 3/4" rather then 1/2". I had also inherited a 1/2" piece of 4x8 from a friend and stored it in my carport, both on its edge and flat on the cement floor. I became even less impressed. It went thru all kinds of gyrations.

Then I ran across some 7 ply, 3/4" plywood from Chili being sold at Home Depot. It was the best looking stuff I had seen,....Radiata Pine
sanded-plywood-1240063-64_1000.jpg


It was a little thicker (and heavier) than I had originally planned, but then again I am not supporting it with 3" wood framework on its edge as in many conventional benchworks, so a little extra thickness could be helpful for both stability and extra cantilivered strength. And if I paint it all around that should help seal it against some of the moisture of humidity.

So next my staging area track plans expanded, and began to interfere with those metal brackets I had selected orginally. Got a new idea that I would weld up my own out of surplus (scrap) steel bed rails/frames.

oops, I was over at my local metal scrap yard this past Fri and noticed some hollow square steel tubing they use to mount street signs with. Its 2" square verses my flanged 1-1.25" bed rails, and its really strong, and its galvanized. So now I am definitely considering this stuff.
31+BB2Dja6L._AC_US327_QL65_.jpg


In the past I have critiqued that I often see benchwork for our model trains 'overbuilt'. Funny how I seemed to be headed in that same direction :)
 
If you look at Ken's (D&J's trains) benchwork, you will see that thickness is what he used. Basically the more plies, the more stable. More work to cut, especially if cookie cutting and if you do that then grade transitions will be longer where they curve up or down. Radiata Pine eh! New Zealand grows a lot of that there. If you can, let it acclimatise for a while where your layout is. It's a soft pine so is moisture absorbent, Primer/sealing both sides and along the edges of cuts will help with that. Steel brackets that you can make yourself will give you the flexiblity to make to the widths you need at any given point.
 
Regarding rail expansion....I didn't allow any gaps in the mainline of my railroad. Ten years and no problems. Laid the track in winter when its cool in the basement and the temperature runs between 66 and 70 degrees.

Greg
 
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A word of warning about plywood. I have watched Chinese-made plywood de-laminate over time. A good friend saved a few bucks buying it, and regretted it as his railroad began to come apart after a couple years. Cutting the stuff smelled bad also. I think the glue was really bad.

Bill
 
From the boating business I have learned to QUESTION all Chinese products. And from Harbor Freight as well.
 
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Better to be safe than sorry. "Things" happen around layouts, people trip, slip and fall when and where you least expect. I can DANCE on my layout, 1x4 pine screwed together the make "2x4's", tapconned to the floor and the frame is all 1x4 pine screwed into the wall. For the top I went with 1/2 inch MDF and it's been over a year in this basement with the sump running almost continuous five feet from the end of the layout and NO warping or shrinking that I can tell has occurred.
 
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