Expansion

[chris]

A common question on here is "How much gap should I leave between my tracks to allow for expansion?"

The common answer is "a bit"

Not a great answer so here goes.

Peco streamline code 100, which we all use, is nickel silver rail (nickel silver has nothing to do with silver, it is an alloy of copper) and it expands as it gets warmer, but how much?

Nickel Silver has a coefficient of thermal expansion of 16nm/m/K which I think means a 1 metre length grows 0.016mm for each degree celsius rise in temp. 0.016mm isn't very much.

Getting practical. If you lay track on a cool day at 10ºc but on a hot day in the sun the rail temp reached 60ºc you'd have a 50ºc rise in temp. Call Peco's yard a metre and multiply by a rounded up thermal expansion of 0.02 and you get 1mm of expansion.

I may have got this wrong, but gut feeling says it's right.

This suggests that a 1mm gap between lengths of flexi should be adequate.

[grockle]

After baffling some of us with the maths and science a much simplier way to lay track outsdie is to keep the flexi you want to use in the airing cupboard for at least 48 hours prior to laying. This way it will have already expanded to its maximum and therefore you can lay the track without any gaps becuase as it cools down the gaps will appear.

Ian

[fungus]

Chris

I did the same calculation as you did before I laid any track. I arrived at about the same figure; 0.835mm for a 50 degree temperature rise. However I then assumed that track will normally be laid in reasonably warm weather, ie 20 degrees, and at the end of our garden it is unlikely to get above 40, even in direct sun. Thus 0.5mm is my norm, slightly more if the weather is cool.

I'm not sure about the airing-cupboard method, unless you also pin the track down to its base in the airing cupboard, or are an extremely fast runner and track-layer!

[grockle]

It worked for me because I just happend to choose one of the hottest days in 2006 to lay my track as well.

Ian

[chris]

fungus said:

I did the same calculation as you did before I laid any track. I arrived at about the same figure; 0.835mm for a 50 degree temperature rise. However I then assumed that track will normally be laid in reasonably warm weather, ie 20 degrees, and at the end of our garden it is unlikely to get above 40, even in direct sun. Thus 0.5mm is my norm, slightly more if the weather is cool.

I'm not sure about the airing-cupboard method, unless you also pin the track down to its base in the airing cupboard, or are an extremely fast runner and track-layer!

I was erring on the side of caution at every stage of my calculations. I agree with you that 0.5mm should be fine, but on record I'd recommend 1mm

[cleanerg6e]

You all seem to be very concerned about expansion due to the suns rays. But what about deep penetrating frosts. Now on this one I'm only going on what I've read in books as we don't get them but once the ground freezes it will eventually thaw and even things like rockeries can be damaged by this action. Model railway lines can open up to such an extent that the joints no longer meet. You have to add more lengths of line and may find you have a longer running line..... by about 3 to 4 inches. The terrible freeze in 1963 may seem like a long time ago and a once in a century event but it will happen again and there will be no fore warning of it occurring. Of course it will all be blamed on climate change and our contribution to it, or yours.

In this part of the world I leave a one to two millimetre gap in the rail joints but as it can be very hot here I don't operate much in the summer months and with covers on my railway the expansion problem is greatly reduced to a point of non existence.

On the subject of hot days 20 to 25 degrees is not hot only pleasantly warm and 10 degrees is positively cold. Well it is in my "neck of the woods".

Roy.