track thermal expansion

C-WW
I'm just finishing my track (Code 100, NS) and need to allow for thermal expansion/contraction. The temperature will swing from 45(non operational) to 85 degrees (F). I'm planning to grind a 30 mil gap to allow for the rail movement but do not know what interval is required. Does anyone know the thermal expansion rate? Thanks, Jim

[ March 28, 2006, 03:35 PM: Message edited by: watash ]

 

Jim,
Just doing the math in my head 30 mil is just under 1/64" (.3969). If so, I'd say this is too small for such a broad temp. flux. You may want to consider 1/32" (.7938) or even 1/16" (1.5875).

2slim

 

1/64"=.0156" 1/32"=.0312"

30mm = (30 divided by 25.4 = 1.1811) so I guess 30mils is .30mm

.30mm= (.3 divided by 25.4 = .01181") just under 1/64"

I have always used .032" gap every 36" and all rails at turnouts. Never had a problem. I only solder rail joiners to one rail, and use a coiled jumper aoldered to both end across joiners. I also nick the inside of each rail on the outside rail of curves. It prevents flanges from "picking" the gap.

 

<BLOCKQUOTE>quote:</font><HR>I also nick the inside of each rail on the outside rail of curves. It prevents flanges from "picking" the gap. <HR></BLOCKQUOTE>

Watash, would you please explain the above in some detail. I have never heard of it.

Thanks,

 

Sorry for the confusion but unfortunately some of us are still in the dark ages and working with the english units. 30 mils in the states infers 0.030" (0.76mm). I was planning to set the gap at 30 mil widths because that's about the span when the rail is cut with a grinding wheel. I was planning to have no gaps on the curves or at the turnouts plus solder all the joints to ensure rail alignment. Then cut the gaps at the straight runs but the span between gaps would be determined by knowing the thermal expansion rate. Also the 30 mil gap would be cut when the room is around 70 degrees (F).
There we go again with archaic units (21 degrees C). The room would drop to aaround 45 degrees in the winter (when not in use but the contraction will probably cause the track to deform. Thanks for the tip on relieving the inside rail edges. Jim

 

Jimnrose, all my micrometers, milling machine, and verniers are in inches, so I still think in inches. Mils must be European , so I am not conversant. I have made drawings on machinery that was to be manufactured in Germany. They required the "Dutch Projection" and all dimensions in millimeters. This was done successfully using the computer. 2slim mentioned that 30mils would be just under 1/64", but it would be just under 1/32" was my point, which is what you were saying. I agree with you.

Chris, about 45 years ago, I quit using 18" radius curves on HO track. I had discovered that too often those ungodly long flanges on (what we called 'toy' HO ready-to-runs) would 'pick' the gap on curves and just climb up over the rail and try to keep going straight. Before laying the next section of rail, we would use a fine cut 4 or 6" flat finishing file, and file the rail head on the inside of the outer rail at both ends. We put a taper about half way to the web that ran about 1/16" (.062") and tilted a degree or so. It presented a slide or ramp effect that the flange would bridge from one rail to the next. There was no sharp end for the flange to catch on and cause a derailment. It is a habit now, and even though I use 30" radius curves and #8 to #14 turnouts, I still relieve (nick) the rails anywhere a flange might catch, like on the turntable etc. When the Manufacturers started cutting down on quality and began making plastic wheels, we couldn't keep them on the track, so nicking gaps was the only fix. Also up until then, freight car trucks had shoulder screws to hold the sides to the bolster which provided a means for the truck to ossilate to follow uneven track like the real railroad trucks do. Some higher priced trucks even had real coiled springs for this. The springs were too strong at first, so we had to add lead weight to colapse the springs a little. Then the springs were made weaker, and a 6oz car would go over a 1/16" hump and would still have all wheels on the rails. Those kind of trucks today cost nearly $6.00 a pair and have to be bought separately. It is sickening.

[ 05 March 2001: Message edited by: watash ]

 

Watash-"about 45 years ago...", careful dude, you're getting dust all over the young-un's
When I see "mils" I think of 'milimeters', which always confuses the H@#L out of me! My theory, 'if it's smaller than a #80 drill- it's Z scale!'

2slim

 

In Canada we were well on our way to be totally metric but many were against it. All changes suddenly stopped as so many people were against it. We do have speedlimits in metric, our dollar was always metric and we buy liquids in metric. Gasoline, oil, paint, milk and any liquid in a container. Fabric is sold in metres and the thickness of plywood is in metric but the size is still 4ft X 8ft. Our American neighbours didn't go for metric and that can cause confusion for drivers especially. Here, our speedometes show KMs per hour as well as miles per hour so when we cross borders we can handle speed limits OK. Personally, I work in metric and in inches and feet depending on what I am doing. Our temperatures are C but in the US its F. We see so much US TV and listen to so many radio stations that C and F can be confusing.
OH well, my rulers have metric on one side and inches and feet on the other. I wonder if it will ever change. Metric makes so much sense that we shoud all be using it.

 

Hey Guys,
I was able to get the expansion rate for NS Code 100 rail. It's 1/8"/ft/degree F. I figure a 20 mil gap (cut at 70 degrees)at 10' increments would suffice for layouts in the north country that could have a temperature swing of 40 degrees (F) or so.
Thanks for your inputs. Jim

 

Hi Guys,

I must give some comments to the thermal expansion issue.

I dont know where 1/8"/ft/degree F comes from, but I think
that watash´s result comes closer.
Look at this. I calculate in metrics but the result must be
the same for temperatures in F.
The expansion coefficient for copper, brass, and silver is
about 0,000019. Even if the temperature swing is 40 C or 72 F,
the expansion will be 0.000019 x 40 x 304.8 (one ft) = 0.23 mm
per ft, which is the same as 9 mil or about 1/128".

Jim, in your case with only 14 C difference it seems OK with
about 20 or 30 mils per each 8 or 10 ft.

In my basement the temperature swing between 15 C (59 F) in
the sommer, and 18 C (65 F) in the winter. That will give an
expansion of less than 1 mil/ft (= nothing in practice).

However, I have had expansion problem twice during the last
10 years, but I have found the reason to be the underlaying
material in the substructure. A greater impact than the
temperature is the differance in humidity between summer
and winter due to the heating in winter, that will do some
material to dry out and give an contraction that the rails
can not follow - and you have a "sun curve".

I might also mention that I have had no problems, with the
exception for the two cases above, and still I´m soldering
every rail joint with rail joiners on both tracks and
turnouts. Some curves I have loosen a part in the middle
to give the whole track a possibility to slide radially.

One good idea from watash (who else?) is that he file the inside
of the outer rail in curve joints to avoid that a wheel flange
is climbing up on the forward rail.
It worked 45 years ago, and it still works.
--------
Helge

SR&WF
NARA member #5

 

Humm...
Expansion of just the track or NS track installed on...what? Cork over Plywood, Pink/Blue Foam over plywood?
I haven't experienced any problem's regarding temperature/humidity with my NS track glued to 1 inch foam that is glued to 5/8 plywood bench.

Rich

Rush Run River Logging Co.

 

Hi All,
The reference document for the thermal expansions rate is Mark's Mechanical Engineers Handbook, 1958 edition p4-7;
stating" 0.0000102 per unit length per degree F within the rang of 32F to 212F for the Coefficient fo Thermal Expansion for Nickel Silver. I converted the #'s as follows: 0.0000102 x 12"/ft x 1000mils/" =
0.1224mils/ft/F or 1/8"/ft/F.
The Atlas flextrack allows the rail to shift along the ties. Bonding the ties to the substrate (cork + wood) without allowing gaps in the rail will result in track buckling if the temperature swings greatly.
In my case the room swings from around 40F thru 80F and I have a large layout. The above data says the rail move 5 mils for every linear foot of track length. Something's got to shift if there is no allowance for the rail movement due to temperature changes. The expansion of metals is much greater than insulators like cork and plywood.
Temperature controlled rooms and relatively small layouts may not need to address this item but I have over 800' of track and want to avoid rail shifting/buckling.

 

I've reread what you said before and I agree with you that you must cut expansion gaps. The reason is simple. You are soldering everything solid. I had missed that little very important item.

 

Roger,
Thanks for your input. Other than soldering all rail joints, DCC applications do not require "power blocks" which behave as expansion joints provided the expasion cycle doesn't produce a short. Plans to include sound chips in the locos emphasize the need for uninterupted voltage source which require soudered joints,clean track rails and relatively smooth loco motion to ensure good power pick-up. Take care, Jim

 

Gee Whizz, I guess I really agree with everybody! I got used to thinking in "thousandsth of an inch" over the last 70 years, so is relatively easey for me. And during some of the years as a design engineer, I was required to make drawings in both first angle (inch) and third angle (metric) style and dimensions. I will admit that designing in metric is easier to the extent that everything in metric is in tenths. I will also agree that when dealing with low voltages and amps, solid connection is mandatory for maintaining a circuit. Where DCC is conserned, and expansion gaps are required, (as for outer space, and cold rooms, etc.) soldering a joiner to one rail and a jumper wire to both rails, solves the problem of alignment as well as circuit. Nicking, or slight tapering, rounding, dulling of the sharp corners of gaps does assist in preventing derails. (A 3 cornered file can assist at a cut gap, so you do not have to remove a rail to reach the gap). I also agree that more trouble is caused by humidity and moisture in the wood and homosote materials than in metal expansion. I also agree that plastic wheels, including the nickle plated ones of today, are the pits with their ungodly long flanges that bump along over rail spikes. The only thing I violently dissagree with all of you on, is the Color! So there!

 

< The reference document for the thermal expansions rate is Mark's Mechanical Engineers Handbook, 1958 edition p4-7;
stating" 0.0000102 per unit length per degree F within the rang of 32F to 212F for the Coefficient fo Thermal Expansion for Nickel Silver. I converted the #'s as follows: 0.0000102 x 12"/ft x 1000mils/" =
0.1224mils/ft/F or 1/8"/ft/F. >

I follow and agree with everything EXCEPT the last statement. 0.1224 mils / ft/ F does not equal 1/8" / ft / F. A mil is 1/1000". So, 0.1224 mils / ft / F equals 0.0001224" / Ft. / F. In other words, as far as we're concerned the rail practically don't expand or contract.

I just calculated, for 200' of straight track, operated over a temperature range of 25 F to 110 F we will see 2" of linear movement. How many of us will have a layout this big that won't show more than this kind of movement on the wood underneath from moisture swings?

I agree heartily that movement needs to be accomodated, but I feel that most of it can be accomodated in the curves with the "slop" in the rail-to-tie connection for the typical layout.

Mark.

 

Mark & all,
Sorry for the confusion its 1/8mil/ft/F.
I'm new to the hobby but have been told by the club members who have their layouts in rooms that do not have temperature control;
that the track should not be glued to the underlayment until a relief is allowed for thermal contraction in the cold periods, otherwise the track will buckle. The math supports their warning for large layouts especially when their are no power block.
Jim