I am starting an HO layout and would like some input on what would be an optimal and a minimal turning radius.
It depends upon the equipment that you plan on running. In general the optimal radius is as large as you can get. 36" is considered the smallest “broad” turn that will handle all equipment. My next layout I am planning on using 63" (12.5 degree) normal and 44" minimum for the mainlines, because I like long passenger equipment. Many (most?) model railroads compromise on 24" radius because that is the smallest some of the larger equipment (Like Walthers passenger cars) can squeeze around. Most HO train sets come with 18" radius and it is sort of considered the “standard”. 22" radius is popular because it is the largest that can make a full turn on a 4x8 sheet of plywood.
Generally 15" radius is considered the minimum for HO but there is lots of equiment out there that will NOT go around a 15". Even some equipment that will go around it looks really stupid doing so.
Im using 31" and some Kato Unitrack. Some are larger.
I have full length heavyweights and other large stuff and must go that big. I dont exactly have a firm plan yet, just flopping track down.
The NMRA recommendations for minimum curve radius based on class of equipment used are here: http://www.nmra.com/standards/rp-11.html.
The Layout Design Special Interest Group has a rule of thumb stating that the minimum radius should be 3 times the length of your longest piece of rolling stock, measured over the couplers. More details are here: http://ldsig.org/wiki/index.php/Curve_radius_rule-of-thumb.
Can you use a smaller minimum radius successfully (meaning the cars don’t derail because the curve is too tight - but they might for other reasons)? Yes, but there are trade-offs. As you use a smaller minimum radius in proportition to the length of the car or engine, adjustments have to be made. Some of the adjustments that are commonly made are:
-
steam locomotives allow drivers to move laterally instead of staying in line with each other. This increases drive friction and requires slop in the drive rods and bearings, often with some negative effect on smooth slow speed performance. In extreme cases, the locomotive will wallow on straight track that is not tightly gauged (most commercial flex track).
-
diesel engines with 6 wheel trucks allow the middle wheels to shift laterally. Again, if the middle wheels are geared, gear mesh can be affected.
-
low hanging details must be made of plastic to avoid short circuits when the trucks with metal wheels rotate the extra amount for the sharper turns. Often low hanging details have to be removed or adjusted.
-
coupling distance typically has to be increased beyond prototypical. Couplers must have wider swing angles, which means locomotive pilot openings are larger than scale. In extreme cases, the pilot is attached to the truck or the coupler opening extends nearly the full width of the pilot.
-
truck mounted couplers become the norm when minimum curve radius approaches 2 times the length of the car or engine. Underbody det
Just a quick additional thought to what has been added in a most comprehensive post above; as you begin to encroach on the minimums in any one system, you increase the probability of errors. In application to a successful, and fun, layout and trackplan, if you use the smallest radii that your rolling items can negotiate, and want them to do so reliably and consistently in a wide range of speeds, you will have to be very skilled in getting your track placed in essentially perfect alignment in all planes.
Failure to be scrupulous about one’s trackwork when intending to run scale speeds with rolling items that are marginal with the parameters is just asking for a lot of disappointment and frustration.
Lesson- always, always, always supply the most generous (wide) curves you can to reduce the frustration factor. It is a challenge in small spaces.
For designing a layout, I thin kthe first reference you want to get is John Armstrong’s “Track Planning for Realistic Operation”. There is a lot of good information in it, you’ll need to go through it more than once. It is written at a deeper level than a lot of today’s “How To” books, in my opinion. It will realyl help you to get a feel for what will fit, and how to design it. The NMRA recommendations are also a very good reference, but the book takes that information (or something very close to it) and puts it more into the layout context.
Welcome,
Given the nature of your question, I would also recommend reading my Beginner’s Guide to Layout Design clickable from my signature. Takes about 5 minutes.
Welcome to this forum! Hope we can be of some future help to you in your modeling endeavors.
The subject of curve radius is almost inevitably the first which comes up in regard to any new design being contemplated. Whenever I begin considering a design for a new layout I have to evaluate the geometry of the area available because that geometry is going to determine what my absolute minimum radius is going to have to be.
As has been stated: bigger, in this regard, is always better. Texas Zepher mentioned a 12.5º curve but, even with superelevation, that degree of curvature is, most likely, going to generate a speed restriction on the prototype. I once belonged to a club that had 80" minimum radius curves and they were absolutely beautiful curves; this radius scales out to 43.5" in N Scale and I sure wish I had room for that size minimum radius but, unfortunately, I don’t and few N Scalers really do. That 43.5" is even broad for HO Scale but they sure look nice.
Your minimum radius is going to be determined by, in addition to your available geography, the type of equipment you wish to operate. Go as big as you can remembering, however, that curves consume a lot of our premium real estate! Before I went any farther I would acquire a copy Kalmbach Publishing’s Track Planning for Realistic Operation by the late great John Armstrong and read what he has to say about considerations regarding minimum radius. He was the dean of track planning!!!
One other thing to remember: A particular manufactures model of a Big Boy may be engineered to negotiate 18" radius curves but it is going to look like a 53" trailer in a cul-du-sac doing it!!!
You could do that, too.[:P] Mr. Mouse has captured the essence of the the non-techie part of Armstrong’s book. His guide would make a really good preface to the book, it gives a good picture of where the process will take you.
If you consider an around the walls layout rather than a 4x8 sheet of plywood you can have a much larger radius and still use the room. When I am an apartment dweller I use a modular/dominos layout with 42" radius. The sections are 18" wide and vary from 36" to 72" long. I bolt the sections together. The layout sections sit on 48" legs, you can still place desk, tables and chairs under the layout and still use the room as a den or bedroom. My last layout was in a 12’ x 22’ apartment living/dining room. The room was useable with the layout in place. Because the layout was around the room I had a removable section that I took out when I was not running trais so we would not have to duck under the layout to enter the room. (Yes, I am married. Why do you ask???) My job takes me away from home for extended periods of time and the modular layout lets me take the train on the road.
JIM
Can you elaborate on your modules? I ma thinking of doing something very similar. My modules cannot be wider than 26" so they can fit thru the basement door. Can you tell me how you put your modules together (I mean did you do end to end, or did you attach them to make 36" width?). I would be very interested in learning how you did yours.
Thanks, Smitty
[quote user=“fwright”]
The NMRA recommendations for minimum curve radius based on class of equipment used are here: http://www.nmra.com/standards/rp-11.html.
The Layout Design Special Interest Group has a rule of thumb stating that the minimum radius should be 3 times the length of your longest piece of rolling stock, measured over the couplers. More details are here: http://ldsig.org/wiki/index.php/Curve_radius_rule-of-thumb.
Can you use a smaller minimum radius successfully (meaning the cars don’t derail because the curve is too tight - but they might for other reasons)? Yes, but there are trade-offs. As you use a smaller minimum radius in proportition to the length of the car or engine, adjustments have to be made. Some of the adjustments that are commonly made are:
-
steam locomotives allow drivers to move laterally instead of staying in line with each other. This increases drive friction and requires slop in the drive rods and bearings, often with some negative effect on smooth slow speed performance. In extreme cases, the locomotive will wallow on straight track that is not tightly gauged (most commercial flex track).
-
diesel engines with 6 wheel trucks allow the middle wheels to shift laterally. Again, if the middle wheels are geared, gear mesh can be affected.
-
low hanging details must be made of plastic to avoid short circuits when the trucks with metal wheels rotate the extra amount for the sharper turns. Often low hanging details have to be removed or adjusted.
-
coupling distance typically has to be increased beyond prototypical. Couplers must have wider swing angles, which means locomotive pilot openings are larger than scale. In extreme cases, the pilot is attached to the truck or the coupler opening extends nearly the full width of the pilot.
-
truck mounted couplers become the norm when minimum curve radius approaches 2 times the length of the car or engin
Optimal is 48", every thing will look great. At 36" every thing will run nicely, but 80’ cars/engines won’t look as good. Minimal is 18", this will run quite a bit of, but not all manufacturers’, HO equipment - long equipment looks freakish on the curves.
As was recommended above get “Track Planning for Realistic Operation”. If you only ever buy one model railroading book, this is the one.
Enjoy
Paul
Minimum of 20 inch radius, optional 24-26 inch
Oh No! Someone threw the N Scale Grenade into the room again!..
A 20 inch radius in the Railroader’s scale is a broad, sweeping arc, with a big 4-8-4 running smoothly around it pulling a train of 85’ passenger cars!
Little trains mean BIG scenery! Take a walk on the wild side…[oX)]
Lee