Measuring Curve Radius

Discussion in 'FAQs' started by Bob Collins, Feb 19, 2001.

  1. Bob Collins

    Bob Collins Active Member

    I suppose for the pros this question is almost too simple to ask, but I want to try to be right the first time. When I am establishing the radius of a curve do I measure from the inside edge of the inside rail to my center point? Does anyone out there feel they have the tied and true method of bending the curve, keeping it to the line you want to establish? I plan to take a yardstick and drill a number of holes to fit a pencil into with a screw at the centerpoint. I'm open to any and all suggestions!!

    Bob Collins
    Rolla, MO USA
  2. BobMcD

    BobMcD Member

    Bob,

    No question is too simple, and I agree--it's MUCH more fun to be right the first time...

    When you're measuring a curve's radius, it's from the CENTER of the track to the radius point. One way folks lay the track with cork roadbed (which comes split into left and right pieces to facilitate smooth corners) is to draw the radius curve with a device such as your yardstick, then lay the inner piece of the roadbed right inside the curve. When it's dry, lay the outer piece of the roadbed.

    Then when the roadbed is dry, lay the flex track smoothly down the center of the roadbed, and you should have a nice curve.

    Bob McD
  3. Bob Collins

    Bob Collins Active Member

    Bob McD;

    Many thanks for the good info. That's makes a lot more sense to me. I will purchase the 1/2 inch oxboard I plan to use today. I am planning to overlay the oxboard with blue board, probably 7/16th inch. I'm told that I will have a quieter operation, although I can't say I've ever been around a quiet railroad!! Many years ago I worked one summer for the UP as a tinner's helper. We were all over the yards in both Omaha and Council Bluffs. Still quite a bit of steam around then (1954, most of which was used to pull fast freights loaded with produce from the west coast. Of course, the huge PFE ice loading area was right along the main line just east of the bridge across the Missouri.

    Anyway, my only concern about building a base that thick was about turnout mechanisms and whether or not I was creating too much of a reach for them up through that much distance.

    Bob Collins
  4. BobMcD

    BobMcD Member

    Bob,

    Well, the sounds of a model train are pretty different from those of the real thing, so some folks like to provide their own sound effects, or at least not to promulgate the funny electric and gear sounds our models make. Of course, if one is modeling an electric cog railroad, maybe model trains give a great sound, just a couple of octaves too high!

    As far as total thickness of the track support (15/16" in your case) affecting switch linkage, if the stuff you're using can provide good support to a small brass tube through it (with a brass rod snugly-fitted into the tube and bent at both ends) and a stable mounting base for your switch machine, you should be home free.

    I did a lot of my train-watching along the Wabash and Frisco tracks in St. Louis as a boy in the 40's and early 50's, so we weren't so far apart.

    Bob McD
  5. Bob Collins

    Bob Collins Active Member

    Bob;

    As you can see on my initial message I live in Rolla, right along the old Frisco Line. There is even an old steam engine in the park alongside what is now the BNSF. I think the # on the engine is 1522. It is apparently identical to the one in St. Louis that is still operational because every once in a while they come down to Rolla to get another part off the one here to keep theirs running. My wife grew up in Silver City, Iowa, right along the Wabash right of way. Now that is a 60+ mile long bike path that runs from Council Bluffs to I think Blanchard, IA.

    I've started cutting my oxboard. It is such a pain for one person to handle. I've got it in the garage where I am doing the cutting. I am tempted to revise my plan and cut it into smaller pieces!!

    Well, back to the saw and saw dust! Thanks very much for the continuous flow of good information. I really appreciate it.

    Bob Collins
  6. BobMcD

    BobMcD Member

    Bob,

    I grew up in St. Louis, but had 4 grandparents in Springfield. We took the train or drove there every month (on Highway 66/I-44) while I was a kid, either stopping in Rolla to change drivers, or riding through on the Frisco. Small world!

    The Ozark Mountains seem like the center of the world to me, even though I live in suburban Boston now. As a boy, I rode behind steam locos in the 40's and later mostly diesels. I was also lucky enough to ride "name" trains from St. Louis to New York, Washington, New Orleans, Los Angeles, and a number of other destinations, on the Texas Special, Panama Limited, Twentieth Century Limited, Spirit of St. Louis, Broadway Limited, and others. My dad had a very good pass for the whole family, and I got some excellent rides.

    Let us know how your model railroading goes. By the way, when you're laying out your curves, if you use a transition curve of larger radius (even 1/2") for several inches at each end of a curve, the whole curve will function like a larger radius curve--it's easy with flex track, and so effective it seems like cheating. John Armstrong describes the technique in his books, as do others.

    Bob McD
  7. Bob Collins

    Bob Collins Active Member

    Bob;

    I don't recall having read anything about transition curves so will do some digging and see what I might discover. Thanks for the heads up on them.

    I have always enjoyed a trip to Boston which would not be complete, of course, without a trip to Legal Seafood.

    I meant to mention earlier that I seem to recall (senility is great) that there were steam engines in the UP yards that had seven foot drivers. I haven't run across any models that I thought were of that particular engine, but maybe too I was just dreaming. I do recall though standing next to one in the yard and the driver was much taller than me standing on the ground and I'm 6'3".

    I'll be happy to keep you posted on my progress. I'd like to finish up my bench work within the next couple of weeks. I then leave for a month in South Africa on a Rotary Friendship Exchange. When I get home I will begin serious work on roadbed and track laying. I have set no deadlines. I'm having a ball and I will not let this fun become stressful!!!

    Bob
  8. George

    George Member

    Hello Bob!

    Glad you found a friend in Bob. Good question up top as I never really thought about it. I wanted to tell you that your idea with the yard stick is exactly what I did and what Bob Mcd. says about how to lay the cork is right on the money.

    I used homasote, and probably always will. If you make a mistake aligning anything it's not a problem. The Blue board you want to use is lighter but I don't know how it holds up to things being changed. Also, if your layout is in an upstairs room or you're in an apartment, silencing the layout from vibration is key. Nothing like driving someone downstairs watching TV nuts with the constant noise that sounds like a mixer running. Good Luck [​IMG]

    George.
  9. Bob Collins

    Bob Collins Active Member

    Hey Shamus, that's really great! I will now need to sit down and see what I can do to incorporate that sort of information into my track plan. Every little bit helps and I have a feeling that will be a big help in at least two places on my plan.
    I've completed about half of my oxboard cutting and sizing and will begin to affix it to the bench work in a couple of days. Then the blue board and I will be ready to get serious about tracing out my track plan. Your information couldn't have come at a better time. Many thanks.
    Bob
  10. George

    George Member

    Bob,

    Shamus is right on target. His blue line is reminiscent of the herky-jerky things we used to design with Snap Track, hugging the edge of the layout.

    His red curve is what they do on the prototype, and what you want to achieve. It looks better to the eye, and will make your long consists appear to "flow" just like the real thing.

    To share an idea the late Master Model Railroader John Nelson once said; "When making a track plan, try and make the entire run one long transition curve." As they say out west, that there's pay dirt! And it's trickier and more challenging to accomplish than you might think!

    George.
  11. shamus

    shamus Registered Member

    Bob,
    A transition curve a way of reducing the angle of attack into a bend.
    Blue line normal curve, RED transition curve.

    [​IMG]
  12. BobMcD

    BobMcD Member

    Bob Collins,

    I'm not an expert on the Union Pacific's steam locos, but they did have some huge "Northern" 4-8-4s with very tall drivers which I believe were about that size. Rivarossi and others make HO models of them.

    Bob McD

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