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switch numbers   Switch/Turnout Numbers

   From S-Trains submitted by SMITTY
   (I added the graphics,PAUL)
   There is a relationship between the "number" of a switch
   and it's radius, although correlating the two gets pretty complicated.
   Basically, the smaller the number, ie, a #5 or a # 6, the smaller
   the radius that comes off the switch. Good for yards or industrial
   spurs, but not high speed. If you were to run your Broadway Ltd. at
   timtable speeds you'd want a # 21 or therebouts when cutting over
   from one mainline to another.

   The number of a switch is derived from the tangent of angle formed
   by the frog of the switch. Use a left hand turnout as an
   illustration. Take your measuring scale and place it perpendicular
   to the left rail of the "main route" track with the "zero" end of the
   scale on the gauge side of the rail. Slide it along the straight
   rail, past the frog until the 1/4" mark rests on the gauge-side edge
   of the outside-of-curve rail of the diverging route.

  Stop here and
   note the place where the "zero" end of your scale is on the straight
   rail. Now measure back, along the straight rail to the "point" of the
   frog, that is, where the gauge lines of the staight rail ( on the
   left side ) and the outside-of-curve rail would intersect. It'll be
   about where the "x"-shaped groove in the frog is, where the flanges
   of the wheels go. If you measured 1 1/2", which works out to be six
   1/4" increments, your switch would be a # 6. If you had measured 2",
   that would be eight 1/4" increments and your turnout would be a # 8 .
   If you recall your trig, the tangent of an angle was the "opposite"
   side of the triangle over the "adjacent". In this case
   the "opposite" side was the 1/4" measurement, and the "adjacent" side
   was the 1 1/2" or 2" measurement. In reality, the relationship is
   actually the arc-tangent ( 1 / tangent ) but that's getting picky !