Turnouts

[Anonymous]

Have read all about turnouts, how they are numbered and why; that as the numbers increase, the curvature of the tunrout decreases; and so on.. but I cannot find anything that tells me what the radius of the curved side of #4 turnout matches up with, i.e. is a #4 turnout equivalent to a 15" radius or an 18" radius? and so on.. There must be a standard somewhere in the NMRA, but it's like everything else.. it's always easy when you know how or know the answer... and impossible to find when you don't. Does anyone have the definitive answer on this.. other than.. gee, I think it's so and so...
Thanks...
Dave

[Anonymous]

My understanding is, in laymans terms... numbered turnouts (#4, #6, etc) aren't 'curved' in their diverging (switched side) routes, but actually 'angled' in more or less a straight line, thus they really don't conform to any particular curved radius. The exception to this, is Atlas "Snap Switches" which aren't numbered, and they're designed with curved diverging routes roughly equivalent to 18" radius curves.

For example, an Atlas #4 switch can handle large 6 axle locomotives because the diverging route is more or less 'angled' away from the main route in a straight line, even though a #4 is roughly the same physical size as an Atlas Snap Switch. The Snap Switch will almost always derail a 6 axle diesel locomotive, because the diverging route is curved to an 18" radius, and larger locos aren't designed to take curves as tight as 18" radius.

I'm sure more people will respond with more technical answers, but that's the basic jist of it, as I understand it.
Thats my understanding anyway.

[Anonymous]

Another thing I believe I read, is a #4 of Atlas, may not be the same #4 of Peco. So the radius of each will be different. I know on a lot of Cad layout software they actually have each manufactures track as templates as they all have some degree of difference. There is supposed to be a formula to figure out the turnout angle, but I think it was Koester in one of the Kalmback books that mentioned the fact that not all #4's or any # turnout is created equal.

[rrinker]

The 'number' refers to how many units of length you travel to diverge 1 unit. Units can be anything, feet, inches, miles - so long as it' the same for both sides. So a #4 turnout diverges 1 unit for every 4 travelled. A #6 diverges 1 unit for every 6 travelled - so you can see the higher the number, the more gentle the divergance is. Now, if you remember trig from high school, you can calculate the angle. I can't draw the triangle here, but the angle is the arctangent of the opposite side over the adjacent side. Since the ratio is always (frog number:1), to calculate the angle of the turnout, it's arctan(1/<frog number>). You cna look this up on a trig site, or just punch in in a calculator and trust me [:D]. So for a #6 turnout, the angle is arctan(1/6) which is about 9.5 degrees. A #4 is arctan(1/4) or about 14 degrees. Again, you can see that as the number goes up, the angle goes down.

--Randy

[NZRMac]

http://www.nmra.org/standards/rp12_3.html#Numbers

I think this what your looking for.

Ken.

[Anonymous]

Thanks to all... I appreciate your time and concern to respond.

[Blind Bruce]

Randy, does the trig work for curved turnouts as well>
BB

[rrinker]

Not really, because of the curve. There is no angle formed, both routes throught he frog on a curved turnout are, well, curved. And here is a big difference from model to prototype. Prototype railroads measure curvature by degrees, the amount of change over 100 feet. A 5 degree curve turns 5 degrees over 100 feet. To further complicate this, the 100 feet is in a straight line - in geometric terms a chord, NOT the circumference of the circle (which would be the actual length of rail used in this case). On our models, we always use a radius number. Curved turnouts are usually specified by the radius of the two routes, say a 28" radius inner curve and a 32" radius outer curve. I'm sure there is a way to plot this out and get a frog number, but it wouldn't be completly accurate using the arctan method because both 'legs' are curved.
For the mathematically curious, I found this web site on curvature: http://www.du.edu/~jcalvert/railway/degcurv.htm

--Randy

[Anonymous]

QUOTE: Originally posted by dthurman

Another thing I believe I read, is a #4 of Atlas, may not be the same #4 of Peco.

That's true -- I read in one of John Armstrong's books (if memory serves) that the Atlas #4 is really a 4.5, closer to a #5, rather than a true #4.

[grayfox1119]

Randy, I am so proud of you!! It is so good to see that a student actuallt paid attention in Trig class!!!!!! Sr. Mary Joan would also be very proud!!