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Discussion Starter #1 (Edited)
Working on a track plan for an addition to my layout. I don't have any of the newer type diesels with three axle trucks. Nor do I plan on getting any due to their size, I think they would look too much out of place on my layout. Most of my diesels are 2 axle trucks. the largest steamer I have is an articulated 2-6-6-2.

My question is what size turnouts should I be planning for diverging off a mainline to a siding and back on and also size you would recommend for yard tracks. I will be using Peco.
 

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A Streamline #5 would be safe for a 2-6-6-2 if you ever have need of it on that spur, assuming it's flanges are compliant with RP-25. Or Code 100, but it would not be used on a spur as it represents 165 lb. rail, of which no railroad used, so if you'd like it to be realistic, no more than Code 83 rails on the spur, Code 70 would be better, and RP-25 flanges should still be good.
 

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I use #6 turnouts off the mainline and #4s in my yards and spurs.
I just bought some Pecos and could only find #5s in code 83.
The packaging says #5.
I don't have any big steamers so cannot comment on that aspect.
Could be a problem with #4s, #5s might work.

Edit. I type too slow, fast fingers mesenteria beat me to the punch.


Magic
 

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Just as an aside, you could probably run some older-era 6-axle diesels (such as SD7's and SD9's) without any problems at all.

Also, the SD35 has the same length as the SD9, will negotiate 18" curves easily.
 

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Turnout sizes

Working on a track plan for an addition to my layout. I don't have any of the newer type diesels with three axle trucks. Nor do I plan on getting any due to their size, I think they would look too much out of place on my layout. Most of my diesels are 2 axle trucks. the largest steamer I have is an articulated 2-6-6-2.

My question is what size turnouts should I be planning for diverging off a mainline to a siding and back on and also size you would recommend for yard tracks. I will be using Peco.
flyerrich;

Peco turnouts are usually sold as "small", medium", or "large", rather than by frog # sizes, as some other model turnouts are. I recommend you adopt the Peco "medium" as your standard turnout, for both mainline, and yard, use. Here's why.

On prototype railroads, its common enough to see a tighter turnout on a siding, or even on some yard tracks, than those used on the main line. However there are some pretty significant differences between the prototype and our model railroads.
For one thing, the frog#s of their turnouts are much, much, larger than any model turnout. In other words they are nowhere near as sharp as what we modelers would consider a "big, gentle" turnout. They also base their turnout sizes on the speed that a train would travel through that turnout. Thus on a high speed mainline, the turnouts need to be quite gentle, and of larger frog #s than those that will only be used by a slow moving switcher. True, we try to duplicate this by running our switching locomotives slowly too, but I don't think most modelers realize just how slowly their model would need to move to match the prototype's notion of "restricted speed."

Their cars are also a lot heavier than ours, and however carefully we lay our track, the super tight curves, and turnouts used on model as opposed to real railroads mean that, let's be honest, we derail a lot more often than they do.

The yard is one of the places on any railroad, where the locomotive is going to be pushing a string of cars backward as often as it will pull them forward. Backing up is harder, in terms of staying on the rails.
This means that, on a model railroad, the turnouts in a yard should be just as big in frog# as those on the mainline. Given the handicaps that we're stuck with, because of space limitations, it's wise to keep our turnouts as easy to negotiate as we practically can.

Besides the largest frog # we can fit, those yard turnouts should be laid out so as to make backing moves as simple as possible
. I'm a big proponent of the "simple ladder" for model yards. This means all the turnouts in a model yard should be identical. All #6 left-hand turnouts, or all #6 right-hand turnouts, for example.
They should also be laid with the main route of all the turnouts forming a continuously straight line, from one turnout into the next. That way a backing train will only have to traverse one diverging route, no matter which yard track it's going to. It also means no jogging from left to right, and back to left, as so many track plans expect a train to do. In short, "keep it simple," and as gentle as possible.

have fun;

Traction Fan:smilie_daumenpos:
 

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My two cents

If you have the space, go with #6 (ATLAS) and/or LARGE PECO or bigger.

Below is a picture of an Atlas Customline metal frog#6 on top of the PECO drawing for LARGE so you can compare. Notice the distance from beginning of points to the point inside the frog is nearly identical. I think PECO is starting to use numbers to describe some of their turnouts. Comparisons are pretty hard when folks start talking about frog angle and such.

My layout is pretty small, so I cannot test a six wheel diesel (don't have one).

But here is a video of a Rivarossi 2-6-6-2 going through PECO MEDIUM and ATLAS #4 crossover, code 100 (Rivarossi flanges are too large for my ATLAS code 83.)

 

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