…how do you figure how much to gap the track when laying it? I’ll probably be laying track (code 83 flex) in the next month or so when the “layout room” (the garage) will be far cooler, 40-50 deg. F, than in the summer (80-90 deg. F). I suppose one possibility would be to wait out the winter and lay track during the warmer months, but I don’t really want to wait 6 or 7 months. Given that there seems to be no real consensus on how much nickel-silver rail expands/contracts, or even if it does (versus benchwork, roadbed, etc.), how does one calculate the number and sizes of gaps?
Before we began construction of our new HO scale club layout, an experiment was conducted with Atlas code 100 nickel-silver flextrack, because we were going to have straight runs of nearly 40 feet along the walls.
Four pieces of Atlas flex track were used. Two sections of flex track were connected with rail joiners to make a 6-foot long section, but were not soldered. The other two pieces of flex track were left separate. All were placed outdoors on a table in full sunlight on a July afternoon when the air temperature was near 100 degrees. After two hours, the rail temperature was checked, and was hotter than the thermometer’s maximum reading of 120 degrees. All 4 rails of the separate pieces, and both rails of the connected pieces, were then careully measured for length.
All four pieces of flex track were then placed into a chest freezer overnight, along with the thermometer. The next morning, the thermometer indicated a temperature of Zero degrees inside the freezer. The track was removed, two pieces were connected together, and the length of all the rail was again measured.
The rail of the 6-foot length of track had contracted less than 1/64th of an inch, and the two 3-foot lengths had contracted an imperceptible amount.
We constructed our layout on hollow core doors covered with two layers of Upson board (Sound board), and cork roadbed. We have had no expansion or contraction problems even though our club is in a non-air conditioned building with no heat in the Wintertime.
Wood expands and contracts with changes in temperature and humidity a lot more than nickel-silver rail, so it’s a good idea to seal or paint both sides of your layout deck, especially if you are going to use plywood.
Since you anticipate a temperature differential of 50 deg.F, rail gaps in the 1/32" range (per length of flex track) should be adequate if your roadbed is moisture sealed (or if you’re laying track on thick foam.) My own tracklaying has to survive about twice that temperature swing, and I discovered that 2mm at 60 deg.F was still open about 1mm at 120 deg F.
On the other hand, if you solder rail joiners, the expansion gaps will have to be wider since there will be fewer of them. I install jumpers around all uninsulated rail joints and leave the joiners free to slide.
There will be some who will tell you that rail can be safely butted tight, no gap, because the expansion is negligible. With all due respect, I built a five track staging yard that way only to discover that rails which had been perfectly straight in March looked like sidewinder tracks in July. That’s what convinced me to pre-gap for expansion.
Slightly off topic, but not really so. When laying track, take a few seconds and a flat file and put a very slight bevel in the top, gauge-side corner of every railhead at every joint. A little touch is plenty - maybe 1/100" across the gauge and 1/16" along the length of the rail - just enough so a finger run along the inside of the railhead won’t encounter any “catchy” spots. If your finger slides unimpeded, wheel flanges will roll unimpeded (and the derailment demon will be very frustrated.)
Chuck
I use gaps of about 1/32" approximately every 12 feet (four lengths of flex track) All other joints are soldered. I also have gaps cut in my main line turnouts for electrical isolation, so some minor movement is allowed there too.
The track is glued to foam roadbed over “pink foam” over 3/8 plywood. Most of it was installed during the summer months. I have noticed that a few, but definitely not all, of the gaps have widened as much as 1/16" from the 90 degree weather of the summer to around 40 degree night temperatures this past weekend. The movement may be due to humidity changes in the benchtop. The trains still run fine.
It is my opinion that curves take up SOME of whatever expansion might occur. If the curves have to adjust excessively, then the rails may just pop off of the ties and that would be no fun at all. I like to play things safe when I can.
Best guess: If you place a 1/16" gap every three sections of flex, you should be OK. If you notice the gaps closing fully when late spring hits, just cut a few more before things get out of hand.
Good luck.
Karl
I don’t do anything scientific at all. I just eyeball in a slight gap every third or fourth section of track. The gaps are in the .030-.050 range, but I never even measure them. They’ve always worked fine.
I’ve heard that point, and actually believe it to be true in some cases, but the results should be the opposite of rail expansion - if the “deck” is expanding due to summer heat or humidity, it should appear as though the rail were shrinking, because the expanding deck would be pulling the rails apart. Likewise, in winter, it should appear as though the rails were expanding, since the deck is shrinking, forcing the rail ends together.
Depending on how well it is attatched to the wood, I think the rail could appear to be pulling away at some points, and pushing together at others. One thing I’ll say is that I’m convinced that any wood in the structure is changing a whole lot more than the rail. The trick (which I don’t know) is to manage the changes in the substrate. Gapping the rails is part of that.
Unless the measuring device did not contract or expand, which is unlikely, I do not see how you were able to measure the rail length accurately at both temperature extremes.
I suspect they didn’t leave the measuring device with the track, though I don’t know that for a fact. I did see somewhere where someone had looked up the properties of NS and actually calculated the expansion/contraction with temperature. It was pretty small, even in our scales. I remain convinced the problem is what is under the rail, in most cases.
The thickness of a business card every 6 feet or so should suffice. Just stick a card in between the rails when you’re joining them.
I’ve not put in these gaps and been sorry, especially if I lay the track in the winter and then summer comes. Even though my layout is in a sealed and heated basement (and typical summer temperatures are 75-85 outside), the rails still popped off the flex track ties. So I got to re-lay the track to fix my boo-boo.
Any material we use to build with is going to move, no matter what we do. The trick is to try to manage the movement, by controlling how the movement impacts the layout. Gaps in the rail, space between plywood sheets, sealing the wood, dehumidifying or humidifying, and temperature control are some the the things we can do. I’m sure there are others, too. We use a lot of different materials, they all react differently to environmental changes, and we have to try to get them to get along.
Hi, I have seen and heard of severe distortion & track buckle when the track was made too rigid by over pinning/glueing and excess paint when painting the track as this in effect glues the rail to the chair. I solder every other joint it’s kind of a trade off beteen electrical continuity and still allowing some give in the track. On the joints that aren’t solder I use loops of wireunder the baseboard. In the past this method has proved very effective in my loft layouts.
Shaun
When I laid my first layout using flextrack (the real first was sectional track) the whole thing buckled in the first Winter. I have been a believer in the theory that the rail isn’t the problem ever since.
One other important point regarding the wood is to make sure you acclimate it to where it will be used PRIOR to working with it (and sealing in my humble opinion). What this does, is let it “soak” in moisture and such in the same ambient environment and then seal it. Therefore, if this seal is not perfect, it should not expand or contract too much. If you use it right from a dry store, it will expand a lot if you have a humid environement and vice versa… Hope this helps.
Brian
Since the 1950’s I’ve found that rail expansion due to temperature is negligible compared to roadbed expansion due to humidity. Once, suspecting humidity was the culprit in constant track alignment problems, my father cut a 3’ section of Homosote in mid-winter when the basement was very dry due to the furnaces running. The next summer, when the basement’s humidity was 100% (condensing on walls and floor) he measured the Homosote with a steel yardstick and found its length had increased by 1/4".
The trick is to avoid Homosote in favor of “Beaver board” or Upsom board" which are much denser and more stable. Avoid large pieces in favor of many small pieces, all glued and tacked to a heavy plywood subroadbed.
It also helps to dehumidify. I’ve found that a small air conditioner running almost constantly during the summer works better than a dehumidifier.
The fact is there are too many variables to determine how much of an issue you’ll have. Other things not mentioned might be that ME flex track has a tighter connection between the rail and ties, and more susceptible to problems. I’ll be gluing rail in some areas using CVT tie strips, and the ties are glued (via the ballast) to the roadbed. The end result is that most of us aren’t engineers and won’t know how much we’ll need. It doesn’t matter what’s causing the expansion and contraction, but it’s a good practice to plan for it just in case. Back to the original question. I decided to solder all of my rail joints, because that’s where the track is the weakest. However, partially to compensate for no flex in the joints, and also to create the sub-blocks for short protection (as Joe Fugate describes on his site), I will be gapping the rails every 6 feet or so. I don’t know the exact dimension, but I’ll be using a Dremel to make the cuts. I will probably use styrene, or the wood gap fillers from Fast Tracks in the gaps to lessen them, but I’ll glue them on one side only to allow some expansion and contraction. I also think that gluing the track down, rather than nailing, can help since the glue has a little give that nails won’t. Randy
Hi Beowulf I am not familiar with Beaver board or Upsom board not heared of it here in the UK are these trade names? if so what is Beaver board?
Shaun
Beaver board and Upsom board are cardboard-like products more like thick poster board (Strathmore board) than the soft Homosote. They are like many layers of paper pressed tightly together and I’ve used 1/8 inch and 1/4 inch thick sheets. It takes about as much force to push a spike into Beaver board as it does to push into clear pine.
I would imagine something similar exists in the UK.
I glue it and tack it to 1/2 inch plywood subroadbed with white glue and a power staple gun then apply a heavy coat of paint to keep out moisture.
It is economical for large areas such as yards but under hand laid turnouts I prefer bass wood or aspen.