Rail Expansion Gaps

Inkaneer Apr 21, 2021

  1. Shortround

    Shortround TrainBoard Member

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    My business cards are .012"/0.29mm. :)
     
  2. Doug Gosha

    Doug Gosha TrainBoard Member

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    My business cards were all thrown away about 6 years ago.

    :D

    Doug
     
  3. Inkaneer

    Inkaneer TrainBoard Member

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    Don't they sell humidifiers where you live? Got one on my furnace and we don't see wide swings in humidity. I also use a good primer/sealer for my modules as extra insurance.
     
  4. NtheBasement

    NtheBasement TrainBoard Member

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    We keep it at 30%, otherwise window condensation damages the frames.
     
  5. Inkaneer

    Inkaneer TrainBoard Member

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    Well, now you got me confused. You have heat, A/C and a humidifier and you still have humidity problems? Something wrong somewhere. That humidifier should be adding moisture to the air when the heat is on. The A/C should be removing humidity when it is on. You say the "...humidity is drier in winter than summer." I'd check the humidifier to see if it is working properly. You may have a problem with the screens in the humidifier being clogged with mineraL deposits left when the water evaporated.
     
  6. NtheBasement

    NtheBasement TrainBoard Member

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    Why do we have a humifier problem?

    Setting the humidity higher than 30% in winter causes condensation on the windows. Condensation drips down the glass, soaks into the wood frames. It's especially bad when temps go below zero, because then the condensation freezes. Its bad to soak wood and its really bad to freeze soaked wood. You can also get soggy insulation that way.

    Hope this is clear. Its set low on purpose. The humidifier works fine.
     
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  7. mrhedley

    mrhedley TrainBoard Member

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    The coefficient of thermal expansion for Nickel is 7.4 x 10-6 inches per inch per degree F. Silver is 11.0 x 10-6 inches per inch per degree F. This is the minimum and maximum you can expect for nickel-silver rail. So in a 100 degree temperature variance, the maximum total change in length is .0132 inches per foot. It will be half that if you laid the track at 50 degrees. Polystrene has a coefficient about 4 times higher than the rail which means of course it will move more than the rail, so if you're gluing track you may want to use a flexible adhesive. I don't glue the track to the roadbed, I let the ballast hold it in place. I've had a longer sections of ballasted straight away buckle, even with gaps cut in the rail every two feet, even though there is probably no more than a 20 degree temperature swing in the basement. Perhaps this is why.
     
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  8. Doug Gosha

    Doug Gosha TrainBoard Member

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    At one time, Model Railroader recommended a latex rubber based medium to ballast track as it's more flexible and quieter than using white glue.

    I have never had a problem using white glue, however. In fact, years ago, I mixed powdered casein glue with the dry ballast and sprayed it with water. Easy. It eliminates the eye dropper/liquid glue step. I may try it again.

    Doug
     
  9. Inkaneer

    Inkaneer TrainBoard Member

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    Nickel silver rail does not contain any silver. It is an alloy of nickel and brass. The coefficient of expansion for brass is depends on its make up since it is itself an alloy of copper and zinc generally having a COE in the range of 10.4-11.4. Nickel's COE is 7.4. Nickle silver rail is generally in the 9.6 to 10+ range depending on how much nickel is in the sample. Note that the formula uses the temperature difference between when the track was laid (usually around 70 degrees and the hottest temperature it will experience. Here we will assume that temp to be 130 degrees. Therefore, that rail experiences an increase in temp of 60 degrees. So we have 60(degrees)X36(length of flex track) (Peco or Micro Engr.)X 9.6 to the 10-6 power. As for the COE of Polystyrene I was not able to find any information that substantiates your claim of a COE 4 times greater than NS rail. That would place it in the area of 38-40+ range which exceeds any of the metals. Highest COE for a metal that I could find was aluminum at about 13.
     
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  10. mtntrainman

    mtntrainman TrainBoard Supporter

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    I use 'Slate Gray' latex chalk to hold down my Unitrack. I lay the track and 'pin' it thru the small screw holes in the Unitrack. I then squeeze a small bead of latex at the bottom edge and use my finger st spread it. A day later I remove the 'pins' In the years since doing it this way I have never had track problems. When I started I used hot glue....but...temp changes in THERR RV just popped the track right away from the glue. The 'Slate Gray' latex is a pretty close color match to the Unitrack plastic track bed...and doesnt look half bad. Latex will stretch a bit during temp changes and expansion and contraction...IMHO
     
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  11. NtheBasement

    NtheBasement TrainBoard Member

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    Just repeating that the coefficient of expansion for the track is orders of magnitude less than the coefficients (both temperature and moisture) of the wooden benchwork and road bed to which it is attached. It makes sense to treat track's coefficient as zero - the exact number is of no importance.

    With solid oak flooring I see tight joints at the ends of each piece one month, and I can easily slide a playing card into the joints at a different time of year. This is closer to ^10-2 than ^10-6. Plywood would be better but not by so many orders of magnitude that it expands less than the track.
     
  12. Inkaneer

    Inkaneer TrainBoard Member

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    Metal expansion is caused by temperature change. Wood is not affected by temperature but rather by moisture. I can find nothing in the literature about temperature affecting wood short of incineration. According to Norm Abram of The New Yankee Workshop fame and other sources, wood expands perpendicular to the grain not parallel to it. So a board will expand across its width far more than its length. Benchwork is constructed with the grain parallel to the floor so any expansion would be across the grain in the vertical axis and not the horizontal. Every source I consulted had the same formula for calculating the expansion of wood across its grain. I could not find any such formula for calculating expansion parallel to the grain. Instead I find statements like this:

    "Movement in a piece of stock caused by shifts in moisture will occur across the grain, as opposed to along the grain. That is to say; a 1 x 6 that is 4 feet long will almost always stay 4 feet long. However, depending on the moisture content of the stock and the air (and the variety of wood used), the width and thickness (to a lesser extent) may vary considerably."

    Dealing with Expansion and Shrinkage in Woodworking Projects (thesprucecrafts.com)
     
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  13. Doug Gosha

    Doug Gosha TrainBoard Member

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    Which is one of the reasons plywood was invented - to somewhat mitigate the expansion/contraction characteristics of wood or, at least, equalize them.

    Doug
     
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  14. Shortround

    Shortround TrainBoard Member

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    As well as it's rigidity and less flexing.
     
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  15. Inkaneer

    Inkaneer TrainBoard Member

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    "Dimensionally stable" is the term that is used with plywood as well as other processed wood products.
     
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  16. Shortround

    Shortround TrainBoard Member

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    Thanks! I'm more used to working with metals and terms can vary. ;)(y)
     
  17. Doug Gosha

    Doug Gosha TrainBoard Member

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    I remember them using the term, "dimensionally stable" when they built a new apartment building here in the seventies. They used plywood "I" members for joists, etc. in the interior and for the decks, outside. When you drive by there, these days, the decks are all saggy and warped. Unfortunately, the plywood absorbed moisture in both directions.

    Doug
     
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  18. bill pearce

    bill pearce TrainBoard Member

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    Thanks to several of qou that have helped put to bed the incorrect statement that track expands and contracts. Plywood, which most of us use under our track, does. I found this out the hard way. After I had enough complete on my cajon layout to allow running trains, I was running a train around the return loop at one end and there was a loud crashing noise. A train went off he track as there was a hump of about 6 inches long and 8 to 10 high in the track. Aw s**t, said i, as I noticed that the plywood had not been painted. Lesson learned.
     
  19. NtheBasement

    NtheBasement TrainBoard Member

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    Yep.

    I try to differentiate between direct observation and something I read. I see gaps appear and close back up at the ends of floor boards. The boards are narrow so gaps on the side aren't apparent to my eyes. The floor is 3/4" solid oak nailed to 3/4" plywood. I'd upload a thousand word picture but the admins are working on a problem with that, but its clear to me that solid wood does expand and contract lengthwise.

    I suspect moisture causes most of the movement. That wood is more stable lengthwise than width wise is well know, a result being the need to float panels in a frame for carcass cabinetry. But no way is wood, plywood or otherwise, temperature stable to anywhere near ^10-6 in any dimension.
     

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  20. Traindork

    Traindork TrainBoard Member

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    Well, the good thing is that having your rail buckle due to temperature is prototypical.
     
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