What is the definition of switch #s

[AF1963]

I have been searching for new AF switches.  I found an S-scale switch on the Ross website.  It was described as a #4.  I have seen these designations used on HO switches as well but I have never seen a definition of what a #4, #6, etc switch is.  It seems all articles assume that one knows what a # whatever is.  Is there a place I can find a definition of this term?

[richhotrain]

AF1963

I have been searching for new AF switches.  I found an S-scale switch on the Ross website.  It was described as a #4.  I have seen these designations used on HO switches as well but I have never seen a definition of what a #4, #6, etc switch is.  It seems all articles assume that one knows what a # whatever is.  Is there a place I can find a definition of this term?

A switch, more accurately referred to as a turnout, is a piece of straight or curved track with a divergent track running from it.

The size of the turnout is indicated by a number. The number is found by counting the number of units in length that it takes to make one unit of width between the center lines of the diverging routes.  For example, a No. 4 turnout will have tracks 1 inch apart, 4 inches from where they begin to diverge.  The higher the number, the longer the turnout.

The NMRA defines the turnout number in more technical terms.  The ratio of the number of units along the center line of a switch frog traversed for each unit the frog spreads to the sides.  For example, a number 4 frog diverges 1 unit for every 4 units it moves ahead; a number 6 frog diverges 1 unit for every 6 units it moves ahead.  Although usually referred to as a turnout or switch number, in reality the measurement is for the frog. A frog is the casting used in the angle where the rails cross and diverge in a turnout or switch.

Hope that helps.

Rich

[lionelsoni]

A mathematical definition of the frog number is one-half the cotangent of half the frog angle.  Some values are:

Frog number   Frog angle, deg
 1             53.130
 2             28.072
 3             18.925
 4             14.250
 5             11.421
 6              9.527
 7              8.171
 8              7.153
 9              6.360
10              5.725

For large frog numbers, 57.296 divided by the frog number is a pretty good approximation.