Switches

[MitchyG]

I was looking at switches, and I want to know what the numbers mean. I'm pretty sure that they have something to do with the curve raidus, but what switch number = what radius.

 

[jeffrey-wimberly]

It really has very little to do with the radius and more to do with the frog. That's the place on the turnout (switch) where the rails cross. As far as radius goes a #4 turnout is many times used with 18" radius. However you can use whatever # turnout you want. I use #4's and #5's.

 

[Selector]

To add, British style turnouts made by Peco do have a radius in the points and on through the frog and beyond. However, N. American style turnouts, just like their real-world bigger cousins, straighten at the frog and continue as tangent track beyond and out of the whole appliance. Accordingly, we don't really talk about radius in N. American track terms, but we use what is called "substitution radius." The National Model Railroad Association (NMRA) site has a section where they give the specs for turnouts of a given design and with a certain frog angle/number. The real radius on a #6 curved British style turnout would be in the order of 28-30" perhaps, just guessing off the top of my head, but the substitution radius of a N. American style #6 is much closer to 42"...quite a difference.

-Crandell

 

[tooter]

..and way on the other side of the switch spectrum my micro layout is going to use lots of #2 wyes...

 

[Cjcrescent]

The numbers used in switch designation refers to the the divergence of the rails. For example, a #4 turnout. From the point of intersection, (this is where the "routes" come together), for every 4 units, these can be inches, feet, yards, whatever, that the straight route travels, the divergent route moves out at one unit.

On a #6, it would be 6 units down and one over, so on for every other switch.

The diagram below should explain it best.

 

[Selector]

Which means that for every unit of axial motion down the major axis of a conventional turnout (meaning, along the 'through route'), if you are actually on the diverging route you can expect X number of units of diversion away from that major axis. And this happens to the truck moving through the first gap at the frog and beyond. The trailing truck and the body of the locomotive above it may not be diverging at all...it's just getting to the points. And this is where knowing how a given diversion angle is going to seriously affect the performance of a certain engine is so important...some long diesels, especially with six wheels per truck, and some long non-articulated steamers, are quite often not happy with #4 turnouts, and will just accept a #4.5...or not. Ya gotta know yer stuff!

One last point: building a layout for today's ideas doesn't do much for tomorrow's wish-I-had-thunk-of-it's. All of us, with very few exceptions, find ourselves wanting something new...or more...or longer....or bigger...something that adds excitement to our hobby. Wouldn't it be a shame if all your carefully laid track, including #4 turnouts, just wouldn't accommodate your new big steamer or SD-70M because they need real 22" radii in order to turn? And even then only at walking speed, not at freight speed?

My point is to consider building in some provision for future/possible needs. Don't paint yourself into a corner, which you will if you have the absolute tightest and shortest of everything.

-Crandell

 

[flyboy2610]

To simplify:
On a turnout (the switch is the electrical device used to operate a remote turnout), from the point where one track starts to separate from the other track, the number refers to how many units of measure (we'll use inches here) the straight track has to run to have one inch of separation from the other track.
So on a #4 turnout, from the point where the rails separate and become two different tracks, the straight track must go 4 inches to be one inch away from the other track, which is angling away from the straight track. On a #6 turnout, you would have to go 6 inches to have one inch of separation, on a #8 turnout you would have to go 8 inches, and so on.
What this means in real life is that the lower the number, the greater the angle between the tracks. So a #4 turnout has a much greater angle between the two tracks than a #8 turnout will. Next time you go to a hobby shop that sell model railroad supplies, compare a #4 turnout to a #8 turnout. The difference will be obvious.
The practical application for this is that a large locomotive does not like to go through a #4 turnout. The drive wheels may bind due to the angle, and it could stop or derail. A small locomotive, or a diesel with only two sets of wheels per truck, would probably not have a problem going through it. A 2-10-4 Texas or a 4-12-2 Union Pacific steam engine would probably not do quite so well.
#4 turnouts are great in freight yards, where the locomotives are usually small, while #6 or #8's should be used any where that your larger mainline locomotives would be traveling. The #4's cost less than 6's or 8's, too, so it's cheaper to use them in freight yards where you would have more turnouts.
Hope that helped!

 

[tooter]

My point is to consider building in some provision for future/possible needs. Don't paint yourself into a corner, which you will if you have the absolute tightest and shortest of everything.

-Crandell

Wise advice, Crandell...

I'm doing this with my eyes wide open, and am specifically planning a micro logging/mining layout with 10 inch radius curves and #2 wyes, so everything I've been acquiring and building is purposefully short...