I've been considering creating a layout and have been doing some research and I'm looking for a quick explanation on why the turnouts have different numbers, what they mean, and which are the best to use for an HO scale layout. I realize that can depend on what type of layout I'm considering. Thanks.
In short terms:
1) For numbers see here:http://www.bachmanntrains.com/home-usa/board/index.php?topic=6140.0;wap2
2) The smaller the number the sharper the turnout departure angle.
3) Regular number turnouts have a straight/angled diverging route
4) Atlas Snap Switches have a radius instead of a straight diverging route. This is so they plug into an 18" or 22" radius curve. (You can make numbered turnouts fit a curve, but they don't plug in like snap switches do, and using flex track for your curve helps make a smooth transition.
5) The turnouts you use are depended are your layout space as you indicated, but also by the equipment you intend to operate. If you're looking to run autoracks, piggyback flats, full length passenger cars, long locos, etc..., higher number turnouts are your friend. Number 6's are a good intermediate turnout that work for all but the longest cars, but also work for a small-ish layout.
Modeling whatever I can make out of that stash of kits that takes up half my apartment's spare bedroom.
The absolute length of a turnout of any particular number, varies with the manufacturer. Length is important if space is at a premium.
#10's are probably more than most people need, #4's in yards probably work best for older smaller cars. It seems that most people post about using #6's for that purpose.
Henry
COB Potomac & Northern
Shenandoah Valley
No. 8: Very long turnout, good for mainline passing sidings and crossovers when the tracks stay parallel.No. 6: Med turnout, good for branch lines and spurs which curve away from the mainline.No. 4: Tight turnout, good for yards or spurs in tight areas.Snap Track turnout: for very tight spurs which will only be accessed by shorter length cars and locomotives.This is just my opinion. I hope it helps.
Think of the turnout as a two-way path. Going the straight way, or what we call the 'through route', you could break it down into units of length...let's use inches.
So, for any one turnout, the path through the frog from the points rails end has two possible components...forward and diverging. The through route has "zero" diveregence since it goes straight...no deviation to the side.
However, the diverging route, the 'turn'out part, diverges so many units of length from the through route with each unit of length one moves toward the frog, through it, and then beyond. That can be expressed as a ratio...and so it's exactly what we do! A #4 turnout diverges one unit for every four units of length down the major axis of the turnout, or our through route. Similarly, a #5 turnout diverges one unit of length to the side for every five (5) units of length on the through route. And so on. The higher the frog number, the more units of travel you must take through the frog and beyond to get the single unit of divergence.
The real railroads rarely use anything less than a #10, and that would be taken at slow speed, say onto a siding where it must stop and wait for an oncoming train to pass on the main. In order for a fast passenger express to take a diverging route at track speeds near 50 mph and up, the turnout would be a #25, give or take...I'm guessing. Such a turnout would eat up about half the length of most of our layouts.
Quick way to 'see' the numbers:
Take a sheet of graph paper - preferably the kind that has more heavily ruled lines an inch apart. Then, place a mark on the base line at one intersection of horizontal and vertical lines, count over the number of boxes equal to the turnout number and mark one box up. Draw a line connecting the two marks. You can make a whole family, from #4 up to #ridiculous, in order to get a good visualization of the size relationships.
Looking at prototype turnouts in my neck of the cactus, I found a #7 (recently built spur to a warehouse) and a bunch of #8s (Older commercial area on the opposite side of the main.) The turnout where the double track through town narrows to single is something in excess of a #16 (I was pacing off the length from points to frog on a public street that parallels the rails.)
Our models can handle much lower number turnouts than the 1:1 scale folks use. OTOH, they have a lot more space to work with.
For what it's worth, the U.S. Army specified #8 turnouts as their standard in manuals written during WWII. That was probably to simplify logistics, a single size rather than a whole klunge of assorted sizes for different purposes. At the time, the Army Standard locomotive was a 2-8-0 built to British loading gauge. Trying to operate a stiff framed 4-8-4 through #8 turnouts would be a non-starter.
Back to models, I prefer #5 for a plain turnout (as did John Armstrong) but more usually bend flex track to the desired routes, mark the tie lines and erect whatever is needed to the dimensions thus established. If you hand-lay your own, you can get away with that.
Chuck (Modeling Central Japan in September, 1964)
J2H DesignsI'm looking for a quick explanation on why the turnouts have different numbers, what they mean
greg - Philadelphia & Reading / Reading
One added note -- the "Number" of the turnout refers only to the frog itself. What happens beyond the frog (length and curve -- if any -- of the diverging leg, etc.) really determines what will fit or won't fit.
As others have correctly noted, every manufacturer's turnouts differ (even between their own lines!) in various dimensions, so one #6 is not the same as another -- unfortunately for newcomers to model railroading. And some are even mis-lableled: the Atlas CustomLine "#4" is actually a #4½. (Which coincidentally makes them a better match for 20-22" radius curves in HO than would be a "true" #4)
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