New 3/4" Scale Track - Part 1

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Mike Walsh
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Re: New 3/4" Scale Track - Part 1

Post by Mike Walsh »

PRR G5s wrote: Sat Feb 13, 2021 10:16 amThe problem is that the expansion/contraction rate of the plastic ties is about 4-5X wood’s expansion rate. Being elevated compounds this expansion/contraction, because unlike on the ground, there is nothing to dissipate the heat. I did consider the expansion of the ties when selecting the plastic ties, but thought the expansion wasn’t going to be an issue. Unfortunately, I wasn’t thinking about contraction. But then I didn’t think I’d be running when it was 45F-50F.

Eric L.
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Re: New 3/4" Scale Track - Part 1

Post by PRR G5s »

Yep, got my rotary snow plow out having fun! Nothing slows the Pennsy down. :D Just kidding, the only thing I’ve done outside is shoveled the driveway once. I see more shoveling in my future, either later tonight, tomorrow, or both.

Eric L.
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Re: New 3/4" Scale Track - Part 1

Post by Mike Walsh »

PRR G5s wrote: Mon Feb 15, 2021 4:48 pm Yep, got my rotary snow plow out having fun! Nothing slows the Pennsy down. :D Just kidding, the only thing I’ve done outside is shoveled the driveway once. I see more shoveling in my future, either later tonight, tomorrow, or both.

Eric L.
Yeah, I shoveled a pathway for the mailman at least so he can walk through without issue.

Probably should have shoveled a path to the street so I wasn't plodding through snow to get to my truck this morning, but it is what it is.
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Re: New 3/4" Scale Track - Part 1

Post by NP317 »

Have had to clear the concrete pad in front of the garage every two days so far. Someone else plows the driveway and road leading to our home.
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Re: New 3/4" Scale Track - Part 1

Post by kcameron »

Eric L,

Do you find the tie expansion more of a gauge issue or between the ends of the rails? I would not figure the expansion of the ties in width would make much difference as opposed to in length. As the ties would expand either way from the center point where the rail attaches to the tie, only compressing the ballast a bit, each tie would 'null out' the tie next to it. But the gauge issue, if enough expansion I could see being an issue.
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Re: New 3/4" Scale Track - Part 1

Post by PRR G5s »

Ken,

In this case, it's not expansion that is the issue, but contraction. In my case, the gauge "shrunk" by 1/32". While you may not think this is not that much, if the gauge is set at 3.500", and using a back to back of 3.281" + 2 flanges at 0.094" = 3.469" which is exactly 3.500" - 1/32", thus causing a steam locomotive to ride up onto the rail in a curve because of the long wheelbase. Even if you do have side to side play in your locomotive.

My engine is able to go around a 20' radius, if the gauge is set correctly. My track has 30' radius, so that's why I knew immediately it was a gauge issue.

My track is mounted to a wood framework, so the ties cannot move longitudinally (along the track), so the rails expand/contract without moving the ties. If the ties do move longitudinally, it's because of expansion/contraction/moisture change in the wood framework, but not because of the rail.

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Bill Shields
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Re: New 3/4" Scale Track - Part 1

Post by Bill Shields »

so...are we all saying: stay away from plastic ties?...unless we live in a temperature-controlled bubble?
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Re: New 3/4" Scale Track - Part 1

Post by PRR G5s »

No, just make sure you take both expansion and contraction into consideration, and where you place your ties. Also the type of plastic you are using, they all have different expansion/contraction rates. In the ground/ballast, you have the ground to stabilize the temperature a little better than out in the open like an elevated track does.

Eric L.
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Re: New 3/4" Scale Track - Part 1

Post by kcameron »

Eric,

That's what I was suspecting, gauge issues mostly. The problem I see is this likely is worse for the smaller scales than larger scales. The tolerances of the smaller gauge gives a range under what the expansion will create. In larger scales you have more tolerance to work with. But I'd have to check the charts to see if the tolerances really follow the scale or not.
-ken cameron
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Bill Shields
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Re: New 3/4" Scale Track - Part 1

Post by Bill Shields »

From an engineering standpoint...the longer length ties which would be expected in larger scale -> will also show greater gauge difference for the same temperature change -> since the growth per degree of change is measured in inches per inch of length.

So the gauge change per degree for a 3/4 inch scale rail setup would be exactly half of 1.5 scale track given the same temperature difference.

Unless I am missing something..
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Re: New 3/4" Scale Track - Part 1

Post by Harold_V »

I don't think you're missing anything. Coefficient of expansion doesn't change with size, it's linear. Millionths of change per inch per degree.

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Re: New 3/4" Scale Track - Part 1

Post by kcameron »

Were these molded ties, with fixed gauge or just plastic stock instead of wood? This is one area I could see the molded ties with fishplates being more of a problem. The plain stock plastic, you could make adjustments for the temperature range for your layout which wouldn't be possible with the molded ones.
-ken cameron
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