Monitoring Layout Shrinkage or Growth

[Lemosteam]

And I was thinking this thread belonged in the crew lonunge and the vidoe was from Sienfeld.   

[peteski]

And I was thinking this thread belonged in the crew lonunge and the vidoe was from Sienfeld.   

The water was *COLD*!
Speaking of Seinfeld, I watched the "George's IQ test" episode last weekend - LMAO.

[narrowminded]

Well, I won't tell yins what just happened when I put some rail on some foam and checked it outside (45 degrees) and then inside (68 degrees).   All I'll say is I won't move a layout in the winter.    Or even the fall or spring.

[peteski]

Well, I won't tell yins what just happened when I put some rail on some foam and checked it outside (45 degrees) and then inside (68 degrees).   All I'll say is I won't move a layout in the winter.    Or even the fall or spring.

And that is just 23 degree difference in temps.  Couple of weeks ago I had 64 degrees inside and -8 outside.

[mmagliaro]

Well, I won't tell yins what just happened when I put some rail on some foam and checked it outside (45 degrees) and then inside (68 degrees).   All I'll say is I won't move a layout in the winter.    Or even the fall or spring.

I, for one, would like to know how much, say, a 4 foot piece of 2" foam contracts with a 20 degree drop.  I always thought that construction foam was more stable than wood.  Is that not true?

[peteski]

I, for one, would like to know how much, say, a 4 foot piece of 2" foam contracts with a 20 degree drop.  I always thought that construction foam was more stable than wood.  Is that not true?

I think it is much more stable when it comes to humidity (which is what I understand is the largest cause of buckled layout tracks).

[narrowminded]

And that is just 23 degree difference in temps.  Couple of weeks ago I had 64 degrees inside and -8 outside.

Yes, Pete.  We had a similar situation here, below zero and the barometer reading was LO.    I wish I had a base board dimension reading from that time but it was the trigger that made me think about this stuff and led to the recent measurements. That was when I had the rails at a crossing narrow and require fixing.  But that was just a humidity issue as the inside temp was pretty stable at 68-70.  Since the rods were installed I've been at 21% and just this evening, up to 24%.  I may measure that later and see if anything has changed for that little bit.

What I did tonight was place two lengths of code 55 flex track on a piece of typical extruded foam base material and took it outside in 45 degree weather.  After about fifteen minutes to one half hour the temperature of the foam stabilized at 45 degrees and I butted and pinned the ends of the rails and then returned that assembly inside.  This would be a temperature change reading only as neither of those materials are really effected by humidity.  The change was 25 degrees, 45 out and 70 in.  The change over 5' was .033" measured with gauge pins.  It moved visibly, such as could be measured with a ruler.   I may try the same thing with some plaster cloth on some foam and see if that's not more stable.  It would be harder to do a fair test quickly with wood products and humidity being so crucial but that would/ will be interesting, too.

What I'm concluding is an allowance of .00028" per foot, per degree change (maybe just round it to .0003"), would be a safe number to use for extruded foam base and only having to compensate for temperature changes.  Plywood roadbed would be a real issue for me with pretty large humidity changes assured but also becomes an argument for using foam and just allowing for temperature changes which seem to be very predictable and also pretty stable in the house.  The method may not be suitable for large layouts but good for most sizes I am likely to encounter.  I'm also suspicious that plywood base would want slightly greater allowance if trying to accommodate both temperature and humidity but I don't know that.  That can also change depending on the wood used, again beyond my current knowledge and not as simply tested.  I will have some data on that by summer with the gauge rods under the door layout.

Then with just this little bit of acquired knowledge I went back and reviewed what was offered by Randgust and a few others on their successful experiences as well as some of the fails offered and it all plugs in.  I'm arriving at some methods and  considerations that I know will work, first time every time, because the science agrees with the experiences.  There's more but I'm comfortable that I'm on to it.  And it brings to the surface a remark by DKS that he's using double backed foam tape for laying track now and that seems to have merit at a couple of levels, maybe even ballasting.   I will be considering that but figure there's still something to learn, weigh, and decide because not all double back tape is created equal.

[peteski]

WOW!

[narrowminded]

I, for one, would like to know how much, say, a 4 foot piece of 2" foam contracts with a 20 degree drop.  I always thought that construction foam was more stable than wood.  Is that not true?

Well, that depends.   As a general statement I'd say that's true but it should be qualified.  And this is based on what I've learned this far from research, a few experiments, and only a little bit of first hand experience.  That makes it limited but what I DO know, I know for sure.

Extruded foam isn't humidity effected but definitely is temperature effected.  The good part is it's predictable.  For most, temperature of a layout's environment is pretty stable so therefore their foam layout is dimensionally pretty stable without giving it much thought.  Until you move it in the winter.   And don't store it in the attic or garage.   Unless you allow for what will happen, of course.   The number to calculate the gaps is provided for any chosen temperature allowances.  I will probably use a gap number on styrene foam in the future that would allow for a layout to be moved in 20 degree weather and eliminate at least that one issue.

Wood is very susceptible to changes in humidity and somewhat to changes in temperature.  And all woods are not the same.  Some research on that topic will show that better than I can or should try to describe.  It also makes it hard to qualify in general terms other than it's a pretty lot and it's all over the place.   Even in my stable temperature, heated and air conditioned house, the temp is stable but the humidity fluctuates pretty dramatically.  From basically zero to the sixty and maybe even seventy percents.  That's got wood moving around pretty good, much more than foam in a stable temperature. 

I'm still getting information on the wood and it's based on a wooden (luan plywood faced?) door and whatever conditions occur in the house so, while interesting to know this one scenario it's limited in use to this situation and can't be broadly applied with a great degree of confidence which goes directly to the reason behind putting a measuring rig under the layout.  Not all see the value in that but I do and for having an honest answer about what's going on.  Eliminates or pinpoints that item should it ever come into question.  In the few days I've had the measurement rig under it it has moved about .010" and with a temperature change of about 4 degrees and a humidity change of about 4%.  Because the layout is basically a 2" foam base glued to the wooden door I suspect that very little of that change is transferred to the top surface of the foam where the track is so suspect that has remained stable.  I don't expect big wood changes until the spring or summer when the humidity comes back and then I do expect some pretty real changes.  Only time will tell for sure.

I tried to research expansion and contraction rates of the foam and learned more than I ever wanted to know about foam except the expansion and contraction rates.  That's why I made my little test using typical extruded foam from Lowes and Atlas code 55 flex track.  That's how I came up with the number of .00028" per foot, per degree of change.  So your question about 4' piece of foam and a 20 degree change would come out to about .023" or if using a rounded number in the calculation, .024".  I suspect I will use the rounded up .0003" as my multiplier and then round that up to the nearest .005".  That would have me setting a minimum gap, if I was laying the track at the max temperature, at .025".  Or two at .013" or......  And if the temperature was lower when I was laying the track, closer to my minimum temp, I'd shorten the gaps accordingly. 

As I mentioned above, one reason this works so well for so many is that they have probably addressed this issue using windage which has landed themselves in a comfortable place supported by the science.  And others weren't so lucky.  By grasping these things it doesn't have to be left up to windage.  It can be known going in and known for sure.

[OldEastRR]

Here I thought the thread heading had to do with having to cut down the size of your layout, or getting extra space to expand into after it's finished. 

[narrowminded]

  That's why I made my little test using typical extruded foam from Lowes and Atlas code 55 flex track.  That's how I came up with the number of .00028" per foot, per degree of change.  So your question about 4' piece of foam and a 20 degree change would come out to about .023" or if using a rounded number in the calculation, .024".  I suspect I will use the rounded up .0003" as my multiplier and then round that up to the nearest .005".  That would have me setting a minimum gap, if I was laying the track at the max temperature, at .025".  Or two at .013" or......  And if the temperature was lower when I was laying the track, closer to my minimum temp, I'd shorten the gaps accordingly. 

@mmagliaro After typing this I realized I didn't really answer your question properly, "What's the expansion of a 4' piece of foam?"  What my test piece was showing and the focus was the differential with nickel silver track for gap allowances.  As such, they are good.  But that didn't correct for the fact that the track moved at the same time that the foam did so if you want the foam only expansion, that would be the differential measured PLUS the track change.  For nickel silver that would be .0000162" per inch, per degree of change which in the example of a 20 degree change over four feet is .015".  Added to the differential measurement discussed above that means the foam alone in a 20 degree change would be .021" for the foam/ nickel silver differential PLUS another .015" (1/64") for the track alone which means the foam ALONE would have moved .036" (1/32").  And that's over 4 feet and can be seen with a tape measure. 

Without correcting for the steel tape (which is about 25% less than nickel silver), at least the trend could be demonstrated as the numbers are big enough to see with the increments on a tape measure.  A longer piece of foam (8') and a slightly larger temperature change (25-35 degrees) could quickly get you in the vicinity of 1/16".  And if there was a desire to do this and also correct for the steel tape measure, that number would be .0000115 per inch, per degree of change.  If you do this make sure you mark directly from inch marks, not depending on the tape hooking the end.   This could also be an excellent teachable moment for your kids (or adults) if they care about these kinds of things.  It's the same principle of how tires are installed and stay on steam locos, afterall.

[narrowminded]

Update on humidity dimension change on hollow core door over 12 days and humidity ranging from low of 21% and high of 44% (2-21) with current at 42% (2-24).  Temperature range was 68 to 70 degrees with one excursion to 74 degrees.  Dimension change was .051" over 6' with the low extreme occurring 2-14 and the highest dimension at present.  I wish I had a dimension reading from the extremely dry days (humidity near 0) that caused the issues that triggered this effort. 

So for a 21% humidity change the dimension change so far was .0085" per foot.  That may still increase even if the humidity remains stable as it seems that there is some lag in the dimension change from the humidity change and the higher levels have only been that for last few days.  I don't know if this change is linear enough to be interpolated but expect to have a feel for that as the higher humidity numbers of spring and summer arrive.  Also how rapidly the dimensions respond to the humidity changes.