Pad-Ply-Pen
Winter is coming 
🎶Tis the season to be modelling Fah la la la 🎶
 But in reality would it be better to lay track point work in the heat of summer 
as any possible future expansion would be minimal with correct expansion gaps.
 Is there an optimal temperature or minimum maximum /expansion gap in mms to be considered when laying track what is the experience of modellers In hotter climates.
Just curious if it makes any difference where you model or what time of the year I was looking at the video of the Petesville layout and noted the smooth running but wondered about warping of timber and the effect of heat on track work in the Southern Hemisphere 
What are the experiences of Northern Modellers regarding the expansion of say a yard of code 75 during a heat wave (I know that’s far fetched 😀 by the way how do they tell the difference between summer and winter in Settle )
PPP
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AHJAY
The realities of a seasonal change are universal.

My approach... based on living in several climates AND having seen a couple of layouts well and truly harmed by not doing it properly.

TEMPERATURE: Choose a median temperature. In AU this will be perhaps 23~25 degrees where the room will vary from a low in winter of perhaps 1-~12 to a high in summer as much as 40 degrees. Allow about 1mm per metre in expansion gaps unless your room is air conditioned properly so stable in humidity and temperature. LESS important with short layout sections of course... but still be careful.

(Unsurprisingly, the prototype does exactly this... for good reason as well. For example the recently laid Darwin to Alice springs line in AU has a theoretical expansion between hottest and coldest well in excess of 1000 meres in rail length... yet it is continuously welded with no expansion gaps.

In reality this was coped with by super-strong sleepers that are very deep in shape and fixings plus a very precise ballast pressure... which forces rail expansion to be lateral ratther than lengthwise. The one section where standard were slightly compromised by a contractor needed total re-laying!)

TIMBER. Acclimatise timber (sheets and sticks) to make sure its already at the moisture saturation levels of an average day in the room. In AU this is several days, UK I guess not so different. Timber expands and contracts quite a lot, so I will always paint timber on all surfaces and edges if its layout critical once it is cut.

METAL does the opposite to timber so if you are making a frame using both wood and metal, do NOT be tempted to "hard fix" layout timbers to the metal. The effect of any extreme will destroy the layouts integrity if you do.

regards, Ahjay
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Bunkerbarge
Whereas expansion gaps on the layout are definitely necessary to avoid very serious flexing it is worth doing some very basic maths to see just what you are up against.

If we assume a coldest temperature in the room of 15 deg centigrade and a hottest of 25 deg centigrade and assume the stainless steel of the track is in the area of 304 stainless steel then the expansion of a length of track two meters long comes out at around 0.3 mm.  This is approximate as the composition of the stainless is not known, although 304 is at the greatest end, and the coefficient of expansion actually varies with temperature but, just to give us an idea, the expansion of a two metre length of track over a ten degree rise in temperature is less than half a millimetre.  I put a piece of 0.5mm plasticard in between the track ends at either end of the straights during construction, which should be more than enough to accommodate the possible increase.  

If you forget, as I did with my first long straight that went across in front of a West facing window and got the afternoon sun, then you will end up with a bowed section of track. 
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AHJAY
The problem with basic maths is that neither the composition of the metal used in the track nor the conditions under which it was drawn then rolled into rail are known. Both make such a fundamental change to the "simple science" math that it becomes wildy optimistic. Additionally, while metal rail expands when hot... as wood heats, it dries and shrinks... compounding the problems.

regards
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Bunkerbarge
AHJAY wrote:
The problem with basic maths is that neither the composition of the metal used in the track nor the conditions under which it was drawn then rolled into rail are known. Both make such a fundamental change to the "simple science" math that it becomes wildy optimistic. 


That is what I said. 

It does however give you an idea of what you are dealing with.  It is NOT wildly optimistic, it is an estimate to give you an idea of what you need to accommodate.  The maths indicated 0.3mm, I have allowed 2 x 0.5 mm which I am happy should be a comfortable safety margin.
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