11-05-2009, 11:22 AM
Selector Wrote:Note that "expansion due to temperature changes" in nickel silver rails accounts for about 15% of the changes we see when our tracks buckle. The heavy preponderance of the buckling effect is due to changes in humidity and the resultant expansion of the cells in the woods we use to construct our layouts. In fact, the expansion is actually due to the rail lengths being pulled away from each other as the wood loses humidity and shrinks. When you see your track gaps widening, it is because the wood has regained some moisture content and had lengthened....thus taking the rails apart from each other. Think about the randomly distributed raisins in bread dough as it rises. As the dough expands, the raisins move further apart since they have no motive power of their own.
It was demonstrated to me mathematically on another forum that N/S rails expand very little over swings in temperature of even 30 degrees. The person proved that a contiguous length of 100' of Code 100 (meaning one monolithic rail length of 100') would expand a whopping 1/4" along its length over a rise of 30 degrees. I suspect that we all have an accumulated total of 1/4" in gaps along our track systems, and that those gaps really comprise a total more like 1/2 - 3/4" on a typical layout. So heat is not the problem...humidity is the problem.
Solder the tangents rarely, and solder the curved lengths often...to get good curves. Let the tangents slide in non-soldered joints to help your system withstand the ravages of humidity.
-Crandell
Our modular club set up for a show in an indoor mall under a sky light a few years ago, we had one member who insisted that we didn't need to leave gaps in the rails at the joiner tracks between modules. He was in charge of the set up that weekend, so he cut all of the joiner tracks to fit precisely between the modules during set up on Friday night. Saturday morning as the sun came up it was shining from the East through the skylight on the West side of the layout and the rails on that side started kinking. We had to remove all of the joiner tracks and cut them shorted to allow for rail expansion. By noon we were doing the same thing to solve the same problem on the ends of the layout and shortly after noon we were doing the same thing on the East side of the layout. The humidity did not change, and I'm sure we had more than 1/4 inch of expansion. The space was air conditioned, but we did get some solar gain, although the skylights were tinted a bit. I doubt if there was a 30 degree increase in temperature, but I didn't measure the rail temps.