Formula for Track expansion, contraction

[johncolley]

Steel coefficient of expansion: Ce=.000015"/ "length/ degree F. I don't have the numbers handy for wood but it is much higher and also variable as it depends on moisture content (ie: relative humidity).

[jwar]

RE lemscate, cacole.
Thank you very much for the info and the time for for your reply. Reworking gaps at end of helex as its a long sodered run.

Again thanks to all the above replys, have a great op session.....John

[cacole]

Several years ago, we conducted an experiment before we started laying flex track for the Cochise & Western Model Railroad Club's 20x40 foot HO scale layout, because we had been having expansion and contraction problems in our non-heated, non-air conditioned clubhouse on our previous layout.

A 3-foot long piece of Atlas code 100 nickel silver flex track was placed in full sunlight on a clear day in early July, between 11:00 a.m. and 1:00 p.m., when the forecast high temperature was 100 degrees F., and both rails were measured. The same piece of track was then placed in a chest freezer and left overnight. Contraction of the rail was less than 1/64th of an inch between 100 degrees and zero degrees F.

Based on this, we left an unsoldered expansion/contraction joint every 6 feet along the layout sides, and we have had no problems. As someone else has already mentioned, your benchwork needs more careful consideration than the track.

The old layout that had been continually buckling on us was 1/2 inch plywood on 1-inch pine L-girder framing, topped with homasote. For our new layout, we used 2x4 framing, hollow core doors, and two layers of Upson board, glued in place with silicon caulking. We have experienced no buckling or expansion problems since then.

[Anonymous]

Nickel silver rail has negligible expansion and contraction for model railroading purposes. According to MatWeb(1), an average composition of nickel silver (every company uses a slightly different alloy) has a coefficient of thermal expansion of 9.11 µin/in-°F. In more legible terms, the rails in one three-foot section of flextrack will expand or contract approximately 3.3E-3 (.0033) inches for 10 degree Fahrenheit increments. Interestingly, this is almost exactly the size of the gaps in the original problematic track. Thus, a good rule of thumb would be to put one Dremel cut off disc wide gap in every three feet of rail per (layout room temperature range/10).

The more serious problem, as mentioned, is in the wooden benchwork. But it's not due to the thermal expansion of the wood, but rather the humidity and water content. On humid days, the wood will swell and throw things out of alignment. This can be solved by drying and sealing the wood before installation.

Of course, the best preventative measure is to build a layout in a heated, air-conditioned, dehumidified room.

(1) http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MCUAEM08

[jwar]

Sounds like my friend has the same problem as "bsteal". Im going to find a temp gauge, chill the track (perhaps when the wifes at work) and make a gizmo so I can check the lenght with a depth mic at verious temps. Now Im realy curious, thinking back a bit I had a problem with the sunlight shinning through a window.

Thanks to all, have a great session. ....John.

[dragenrider]

I've read a lot of comments on expansion and contraction of tracks. My railroad is in a garage which is poorly heated or cooled. Sometimes it gets hot as [}:)] in there. I've had no problems with track misalignment.

I contribute this to two things:
1. I accidentally left a lot of gap between rail sections in certain areas. As the rest of the track is soldered, it gives the rails some where to expand.
2. All my track is sitting on foam roadbed which in turn rests on Styrofoam. No wood contraction here!

Maybe this will help others in laying their track. [^]

[bsteel4065]

It is dependent upon the temperature range. My layout was in my attic / loft and during the summer the expansion of the track (Peco) was BIG. I actually had twists in the track. Come the fall, it was fine. It was so hot up there in the summer that railroading was a fall / winter / spring pursuit. Forget it in the summer.
My new layout is going to be in the same place but this time I'm going for AC.

[jwar]

Very interesting...My friend only has problems with excessive heat in his train room. No insulation and no AC. When he came back from vacation for a week, his turnouts were trashed, guide rail, points and broken ties.

Illl take your word for it, benchwork expands more then rail, However if his bench work, solid ply expanded more then the rail, in my way of thinking the joints would be looser. Now Im wondering as I type this,could the layout expanded pulling his turnouts apart.

Weard to say the least, Thanks Dave...take care and have a great day.

[dehusman]

After many,, many discussions on this, the actual expansion and contraction in the metal is very small. There is more expansion and contraction in the benchwork and subroadbed due to humidity changes than in the rail.

Dave H.

[jwar]

A friend who is using code 100 with Shiohara turnouts has so much expansion the turnouts are breaking up. I believe due to the small plastic turnout rail spikes and only the width of a dremel cut off wheel .0035 gap.

However my question is how much will a section expand (36 in) as I just put in about 80 feet of track in a helix. I left quite a bit of space between track nails to let it float a bit, side to side.

I gap straight sections about .021 (thickness of NMRA HO gauge) and soder all curved sections. Winter to summer temp from approx 38 to 100.

I started to place a section of code 100 flex track in the fridge to later set in in the sun to get and idea of expansion. My wife kind of changed my mind on that. Stateing she knew how much I enjoyed hot meals and sleeping indoors and highley sugesting me using this forum.

I dont think my helix will be a problem. but later ballisting other long curves may, as the track expands.

A note of thanks for your reply, as the information on other posts were terrifficccc info.