15 1/2 gauge radius calcs

Discussion in 'Track Planning' started by dparks, Jun 25, 2005.

  1. dparks

    dparks New Member

    i am putting in a new track and need help with radius caculation and grade for my 15 1/2 gauge 4-4-0 plenty of room for train 43 acres to work with i just need to know minimum radius this engine will negotiate without derailing

    Attached Files:

  2. Matthyro

    Matthyro Will always be re-membered

    Welcome to the Gauge

    All I can say is WOW. 15 1/2 gauge eh! and 43 acres. Any photos of your 4-4-0. We would love to hear and see more of your railroad
  3. Pitchwife

    Pitchwife Dreamer

    Hi dparks
    Grab yourself a calculator, even the cheapies have enough funtions on them to do the trick.

    Radius is the good old 2PiR squared. Measure the widest part of the layout or where you want to make the corner. divide that in half and put a pivot point (nail, stake, whatever) there and tie a string to it Take the end of the string and keeping it taught, go around and mark where the end of the string is around the perimiter. That is the outside of your curve. Don't forget to allow for clearences, etc. Change it around if you know what diamater curve you want. Measure the radius on your string and set your outside pionts first then locate the pivot point and do the same thing.

    Elevations are a little trickier, that's where the calculator comes in. I use triginometery since I use it for other things and am used to it. First you have to know two of these three things. 1. How high will the elevation be. 2. What angle do you want the rise to be, or 3. how far do you have to do the rise.

    It you know 1 and 3 then figure out your hypotenuse by squaring 1 (the distance times itself) and 3. Add the two numbers together and find the square root of that sum. The square root sign looks like a capital L layed on its side. That number is the length of the hypotenuse.

    If you know 1 and 4 divide 1 by 4. Then push the sin button and that is your grade angle, 2.
    If you know 3 and 4 divide 3 by 4. Then push the cos button and that is your grade angle, 2.
    If you know 1 and 3 divide 1 by 3. Then push the tan button and that is your grade angle, 2.

    If you know what you want your grade to be and want to know either what elevation or distance you need let me know and I can go over it. Either way you have to know two of the first three measurements.

    This will either help or totally confuse you. :D :D :D :D

    Attached Files:

  4. dparks

    dparks New Member

    additional info

    thanks for the help but what i really need is to know how to determine the minimum radius my train will negotiate without derail
  5. siderod

    siderod Member

    I work with 7.25/7.50 Inch Gauge stuff, so i'm not really sure how small a radius the locomotive would take without hittin the ground. But, if you've got 43 acres to play with, why worry about radius? The wider the better?

    On that note, is your 4-4-0 actually live-steam? or do you have some other sort of prime-mover stashed away inside it? I ask because i don't see steam, water, air or oil lines anywhere on the locomotive.

  6. dparks

    dparks New Member

    prime mover of my engine

    no live steam yet she has a 5 hp motor with a riding lawnmower transmission
    the problem is i have the 43 acres broke up into pastures for my cows
    and every year i decorate one pasture with 1/8 mile of christmas lights i would like to set up the train to circle a 33 ft high christmas tree during the month of dec and run it on other track during the rest of the year so i am trying to find out how tight of a circle i can put around the tree, i am also looking for some trucks to build two passenger cars and a cabose
  7. SAL Comet

    SAL Comet Member

    I second Robins WOW, beautiful loco. Did you build it your self? As for the min. radius, I don't think such a thing can be calculated due to the number of variables involved. Because the wheel base is short compared to the track gauge, the loco alone should manage a really tight curve. The limiting factor IMHO, will be the length of your passenger cars and how they are coupled. I think the only way to find out how tight a curve the train will negotiate is by trial and error. Mabye set up a short test track and keep making it tighter and tighter till you get a derailment? hth
  8. dparks

    dparks New Member


    no i did not build it myself but i added power and drive train to it
    i also added wiring and steam whistle system to it
    i bought it in lousiana about 75 percent complete
  9. sumpter250

    sumpter250 multiscale modelbuilder

    Have you contacted the manufacturer to see if they have a recommended minimum radius? If that is not an option, see if there is a site for that gauge, and see if someone there can answer your question. If not, then trial and error is the only way.
  10. dparks

    dparks New Member

    unfortunatey the builder is dead and he had no company
  11. MasonJar

    MasonJar It's not rocket surgery

    Sorry to disagree clark, but radius is the "R" in 2PiR^2 (R squared). 2PiR^2 is the formula for the area of a circle, also expressed as PiD (D=diameter, D=2R).

    dparks - without any other information available, I would agree that trial and error is your best bet. I don't think that grade will betoo much of an issue with the lawnmower engine. Your limiting factor is likely to be the couplers/rolling stock length as mentioned above.

  12. pgandw

    pgandw Active Member

    Scaling up from a 36in radius in 0 Guage - a very conservative minimum radius in scale for a 4-4-0 - gives a minimum radius of 37ft. So I recommend starting with about 24ft radius for your trial and error.

    From what I have seen in the smaller guages, 2 to 2.5 times the length of the engine or car seems to be a reasonable rule of thumb. As others said, your passenger cars may be more of a limit than the locomotive.

    Can I ride when you get it going? Sounds and looks like a lot of fun!
  13. cidchase

    cidchase Active Member

    Hi dparks,
    What is the dimension from outside to outside of the driver flanges?
    This should always be somewhat less than the track gauge, maybe 1/2 to 3/4"?
    What is the tread width?
    What is the diameter of the tread and the diameter of the flange?
    What is the driver axle-to-axle distance (wheel centers)?
    How much side-to-side motion is provided in the pilot?

    With these dimensions one could CAD the wheel arrangement and come
    up with a theoretical min. radius for the loco itself. The drawbar should
    have enough pivot angle not to be a factor.

    The coupler arrangement may also affect the min radius at which you can operate.
    What is the distance between the pivot points of the couplers on the tender
    and the next car, when coupled?

    How great an angle can each coupler pivot from side to side total?

    If you just scale up from HO you get something on the order of 30-40 ft.
    depending on how generous you want to be. :D :D
  14. dparks

    dparks New Member

    well when i get it operational i will post it here but you are welcome to come ride after i get the track in but it may take me a couple of years unless i find some local volunteers to help
  15. dparks

    dparks New Member

  16. dparks

    dparks New Member

    i will go get all the measurements andpost them later today
  17. dparks

    dparks New Member

    ok here they are engine length is 78" front wheels are 5 1/2" dia.
    center on front axle to second axle is 11 1/4"
    center of second axle to 3rd axle is 20"
    center of 3rd axle to 4th axle is 17 1/2"
    driving wheel dia. is 14 1/4"
    rail area is 1" all wheels
    flanges are 1/4" wide all wheels
    font truck can piviot 1 1/4" off centerline or side to side 1 1/4"
    drivers inside wheel to inside is 14 3/4"
    front truck inside to inside wheel is 14 1/2"
    wheels same as front truck on engine except 7 1/2" between wheels on trucks
    front axle centerline to rear axle centerline of tender is 26 1/2"
    coupler is 8 1/4" long movement is about 60 degrees
    if you need more measurments let me know
    thanks for the help
  18. cidchase

    cidchase Active Member

    Hi d, here's a rough layout of the wheel treads with rail interference points.

    Based solely on the measurements shown, the loco binds on 30' and clears
    on 35'. For appearance sake and a good margin I would go 40'.
    The dimensions on the pilot make a lot of difference, so if the pivot point
    is shorter, for example, the radius could be tighter. You will lose some realism
    the tighter you go.

    Anyhoo, that's my best guess at this point....
    :D :D :D

    Attached Files:

    • 15.JPG
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  19. dparks

    dparks New Member

    the pilot point on front truck is in the center of truck not toward drivers probably won't make any differance looks like some nice software you have i think we are going to try a 40 ft radius on all curves and hope for the best from there thanks a bunch for all the help

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