Peco Turnout Radius

Discussion in 'N Scale' started by Hoss, Jan 22, 2003.

  1. Hoss

    Hoss TrainBoard Member

    Does anyone have a link to something that would tell me the radius of Peco turnouts? I'm using Code 55 Electrofrog and I need to know the radius for small, medium and large radius turnouts so I can decide which ones I want to use where. Anybody??
  2. mdrzycimski

    mdrzycimski TrainBoard Supporter

    Go here and click on the PECO button on the left hand side of the page. Scroll down a bit and you will find what you are looking for and more.
  3. watash

    watash Passed away March 7, 2010 TrainBoard Supporter In Memoriam

    Turnouts do not have a "radius", they are designed to have a degree of frog angle.

    We can not use a turnout as a true part of a curve. The diverging track through the frog and beyond is straight, so are the point rails. Only the diverging rail between the point rail and diverged frog rail is curved.

    In real life there is no such thing as a #4 switch (turnout) for instance, nor a #8.

    Switches are a combination of two assemblies, the frog, and the point rails, connected only by a parabolically shaped diverging rail. (That means the curve of this rail is not a true radius, but starts straight and gradually curves greater and greater until it matches the angle required to match the frog to be used.)

    But on a few industrial tracks and mines or docks, where only an 0-4-0 engine will go, a switch this tight would be designated by the frog angle, such as a 20 degree. Some toy or model switches diverge at as much as a 30 degree angle and is the reason your 6 axel diesels derail easily trying to go through.

    A real railroad's high speed mainline switch has a frog of only 2-1/2 degree angle.

    All switch points are about the same length, which is just enough to allow the 1-1/16" clearence (gap) for the wheel flange width. (When worn to 1-1/4" they must be replaced). The same is true on the guard rails on the opposite rail.

    The diverging (curved closure) rail will only bend enough to align it tangentally with the frog section which is about 5 feet before the frog point, and for five feet beyond, where the running rail continues some more feet ending at what will either be the start of a straight section of track, or the point of tangency to a curved track's easement.

    Our toy or so called "scale model" store-bought switches are mostly the same way with the exception that our switches have a huge gap to clear over sized flanges, and for space reasons, are curved far greater than any real engine would negotiate.

    They were originally manufactured like Lionel toy train track to fit in limited spaces, and continue to be to this day.

    Hand made switches, except for the extra wide gap for flanges, are usually more to prototype "scale".

    For your own understanding, you may wish to lay this out on a large sheet of paper to some scale accurately:
    Draw a long straight line left to right. Make two marks across it, one at the left end, the other at a scale 70 feet toward your right. At this point swing an angle off to one side at 11 degrees then make another mark at 15 feet on line #2. At this point, again swing another angle at 11 degrees more and draw a third line and mark it at 70 feet.

    Now, use a compass, string or yardstick and strike an arc from each of the four points you have marked on the three lines. Where these arcs all cross together, is the radius of the curve required for two 85 foot dinning cars to be able to go around a curve that would have its center on all four of the crosses. The reason is the a standard freight car coupler can only swing 9 degrees to either side, and a passenger car coupler can only swing 11 degrees to either side before derailing the car, or breaking the knuckles. That is in real life, of course.

    An 85 foot diner is about 70 feet from center to center of its trucks. (You can get more accurate than this.) But now you see why you can't expect to take two passenger cars through a #4 switch "in scale".
    The tightest switch I have blue prints for, is what we would call a 7 section or 8 degree 13 minute frog angle, and they are not certified for passenger car use, in yards.

    There is still no real curve radius on model switches either, they are just made with such tight "radiused" diverging curve rail, that they appear to be true radiused curves. (Some cheap ones may be).

    You will have to figure what the angle of the diverging track is, then pick a point somewhere around the curve you wish to use, and mate the tracks there.

    The easiest way to do this is to use a yardstick with another nailed on top at one end. Lay the bottom stick on the straight through track and open the top stick (like sizzors). Slide the sticks along over the switch until both sticks exactly match both the straight and diverging tracks. Now make a mark along the inside of the top stick so the mark appears on the bottom stick. This is the diverging angle, the same as the frog angle.

    Another way:
    Lay a complete circle of the desired "radius" you want to use, and slide the top stick around this circle until the bottom stick is in line parallel with the straight track. Where the top stick exactly matches the curved circle of track is the "point of tangency" (where any curve starts from any straight).

    If you draw a line at 90 degrees to the angled stick, it would cross the center of your curve track's radius.

    If you have a full 180 degree return loop at the other end of an oval of track, you would not be able to use the full 180 degrees of curve at the switch end because the switch is in the way. By cutting the correct amount off the curve, you can fit the curve to the switch at the mating angle, and all tracks will remain parallel. But the switch is not a part of the curve, only a "lead" into the curve.

    If you fail to do this, you will have a kink in your curve, and will have derailments. See?

    Another way:
    Let us say you have already laid a full 180 degree loop and now you want to add a switch so a straight track can continue on to go somewhere.

    You want the straight track through your switch to be parallel to the other track on this loop.

    At right angles (90 degrees) to that other track, draw a line through the center of the loop's radius and cross the place where the switch's straight track will be.

    You know the frog angle of the switch, so go to the center point of the loop, place your yard stick on the center, and swing the stick around the loop until you have the stick at the same angle as the frog, and draw a line.

    Where this line crosses the loop, is the amount you must remove from the loop to allow for the switch.

    Simple geometry. Now you know why the teacher tried to get you to learn geometry in school. See? We do need it in real life! :D

    [ 22. January 2003, 17:24: Message edited by: watash ]
  4. Harron

    Harron TrainBoard Supporter

    Excellent description Watash, but what holds true on the prototype doesn't necessarily in scale. There are model RR turnouts that are designed to have a radius through the diverging route. Peco's are an example, along with Atlas Custom-Line turnouts (19" radius).
  5. watash

    watash Passed away March 7, 2010 TrainBoard Supporter In Memoriam

    You are correct Corey, that is why we have derail problems through the big gap where the wheel falls off the diverging closure rail's wing and has to climb back up on the frog's point. It makes our cars wobble going through here enough that some actually will bounce up allowing the flange to ride on top of the frog and derail, especially on what we call a #4 switch (turnout).

    You jumped in while I was checking some dimensions, Corey, but I looked, and I don't have any Peco switches that have a true radius, mine all have the straight section through the frog area, and the diverging closure point rail is slightly curved too, like the real switches I have seen. But the smallest Peco I have is a #8 and the largest is a 14.
    It must be the smaller ones that have the full radius closure rail. I can see why they would make one this way.

    The switch blue prints I have has the smallest tightest mainline frog as an 8 degree 13 minute frog angle noted as a 7 section frog, with various lengths of closure rails for yard, or crossover use. I made a 10 section to print that has the 2 degree 30 minute frog, and it came out at 14" long. It is really a smooth switch too.

    When I ran the steamer, we called it a switch, then when I became a designer, I was "educated" to call it a "turnout", and a switch became the thingy we flip to send electricity from one place to another. I guess nowdays they call the whole track arrangement a turnout. Only the point rails do the "switching" from one track to another, so we called the whole thing a switch.

    I guess the manufacturers had to make Lionel type switches to save us space. If we had to use #7's for yards and 10 and 14's for mainlines, we would have to have Grand Central Station to put the layout in. :D

    [ 22. January 2003, 17:38: Message edited by: watash ]
  6. Hoss

    Hoss TrainBoard Member

    Actually, Peco Code 55 turnouts all have a frog with a divergent route of 10 degrees (#6). Unlike many other turnouts, their difference is in the radius and not the frog. I have since learned (thanks to the link provided above) that the small radius is 12", the medium radius is 18" and the large radius is 36".

    My second question is an effort to make more efficient use of my yard, I'm considering using the small radius turnouts for the yard area. Will modern 6 axle diesels and long cars (autoracks and the like) negotiate 12" radius curves? How do they look? The smallest radius on the rest of my layout is around 24".

    [ 23. January 2003, 03:22: Message edited by: Hoss ]
  7. BarstowRick

    BarstowRick TrainBoard Supporter

    Do I dare jump in here. I dare. Here is another alternative simplistic as it be. I do like the geometery approach as described by Watash. He has done a excellent job describing a switch and how it works and all the fun you can have installing it.

    One quick way to determine if a switch will fit into a diverging route you are planning, is to take some pre-fab sectional track and place the various curve sections over the switch in question...until you find one that closely corresponds. Keeping in mind as Watash said, the switch has a straight section prior to the diverging points. In some cases you can cut the straight section off in order to custom fit into a curve section of track. Another thing to consider with Peco, is they do indeed have curved turnouts on a rather large radius. I've used them and haven't had any derailment speak of.

    Look at the instructions that come with the Peco switches (turnouts) and you will note some instructions with regard to the curvature. Oh, and they are appropriately refered to as "Switches" as per good old American railroad lingo.

    Hope this helps.
  8. dstuard

    dstuard TrainBoard Member

    Only you can decide how much space to allocate to your yard and yard ladder, but I think if you lay down some track with small radius turnouts you'll find that it looks awfully toy-like.

    On my NTrak module set depicting the small yard at Colfax, CA, I went with Peco large radius turnouts throughout, both for looks as well as geometry (the engine service tracks are at an angle to the main, and smaller radius turnouts would have made the angle too severe).

    Consider also that in a yard there will be lots of switching and potential backup moves, possibly through reverse curve configurations. That is hard enough as it is without adding tight curves and sharp angles to the mix, particularly with modern era, long wheelbase equipment.

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