Hi, my friend want to build an HO scale layout and he would like to know what is the minimum width his layout should be if he want one of his train to go in the opposite direction? And I would also like to know the answer for N scale because that’s what I’m going to build.
Thanks for your help!
An train going by the smallest possible radii curves 9 3/4 curves is probably a 1.5 feet, 11 3/4 R curves is about 2 feet about an inch short of 2 feet even on both sides of the semi circle.
It will depend upon the size of the locomotive.
That is why most manufacturers indicate the radius(turning) circle.
It only makes sense that a small switcher would require less space than a larger engine
Most smaller HO locomotives and rolling stock were made to negotiate an 18 inch radius curve, which would be 3 feet across. You also need to allow for extra space on the sides of the curve, so a 4 foot wide piece of plywood is usually considered the minimum for HO track.
To deterninine minimum radius neeeded look at NMRA Recommended practices for the type of equipment you plan to operate.
https://www.nmra.org/standards
Then go with a larger radius if you can.
The real question is “What minimum radius will I accept on the main line?” Which depends. In HO most equipment will stay on the track and go around an 18 inch radius curve. Going below 18 inches is perilous, much equipment won’t stay on the track. HO train sets are traditionally sold with 18 inch radius curves. Manufacturers want to tap the huge train set market, so much work is done to insure that the rolling stock will indeed keep rolling on 18 inch curves. Exceptions to the 18 inch rule are full length passenger cars, large steam engines, some large diesels. If you stick to 40 foot freight cars, four axle diesels and smaller steam 18 inch will work for you. To avoid a surge of product returns and the resulting customer and dealer ill will, HO makers will put a note on the box of equipment that requires more than an 18 inch curve. If the box doesn’t say “XX minumum radius” it is safe to assume it will stay on the track.
An old rule of thumb says “use the broadest curves you can squeeze in”. The trains look better on broader curves, derailment happens less often on broader curves, and sooner or later the urge to run full length passenger cars will strike you.
Given that you have settled on your minumum radius, to do a 180 degree curve (a turn around loop) you need a table width of twice you minumum radius, plus a couple of inches. Curve radius is measured to the center line of the track, so you need a little more t o keep the ties from lapping over the edge of the tab
Dstarr, I did answer earlier and you reminded me about broad curves in N, Thank you!
the largest Radii I currently possess is 18.75 R in N scale and that is very close to 3 - 3.5 feet wide. Jumping down to 15R that would be probably about 2.5 - 3 feet wide atleast(not sure because I do not possess an entire curve
Ok so for me (N scale) a table of 24 inches large should not be enough for a complete turnout?
24 inches would be plenty of space if you use 11.75 R track to do a turnaround.
Ok thanks Gary!
Stef
From my own experience, in HO, using the Peter Josserand definition of, “Train - A locomotive (or locomotives) with or without cars, carrying markers:”
A Varney Dockside (B&O prototype 0-4-0T) was once run on a circle of track the inner rail of which was a silver dollar.
4-wheel Birney streetcar (“Toonerville trolley”) ran on 100mm radius, with a roadbed width of 12 inches. That allowed HO rubber-wheelers to be parked between the track and the edge.
The Tomikawa Tani Tetsudo runs short cars and a very flexible (Mantua) 2-6-6-2 on 350mm radius. The duodecagon roadbed for the spiral is 940mm across - 32 3/8 inches. Standard American freight cars and locomotives are embargoed from this route, as are most JNR locos, long freight cars and passenger stock.
Minimum radius for ‘toy train’ track and rolling stock - 18 inches. A little space for easements gives a table width of 42 inches (track gauge for my wider-gauge prototypes.)
Minimum JNR mainline radius on my layout, 610mm (24 inches,) adequate for the rolling stock (the long cars are equivalent to the old shortened Athearn passenger cars. Minimum table width (with safety fences) four feet five inches.
If you want to run humonguboxes, auto racks and your model of N&W’s Jawn Henry, you will need a radius of more than 30 inches, and a table width of close to six feet when considering easements and safety margin. (Most such layouts fill a large room, running along the walls with a peninsula or several.)
For N scale, use 55% of the above.
Chuck (Modeling Central Japan in September, 1964 - in a double garage)
You’re very welcome!
this is 18.75 R with two 4.25" straights in the middle of the curve 
the video demos 11.75 R curves http://www.youtube.com/watch?v=SNrMa9ulmXo
All,
I did a little test myself in HO Gauge, & here are my feelings & opinions (stress on opinoins)…
Found a couple of HO Kato 24" (22.5 Degree R) [Part# 2-220] UniTrack
I assembled four of them in a semi circle & set up a temporary foamboard base.
I put on variuous cars & lokies, & starting small & observered their tracking & overhangs.
When I got over a 40 ft cars, & loki’s, I was fairly suprised at the sensitivity of car length, & coupling angles I needed to address.
When I put an Amtrack set of Long Superliners on it, I was almost was Hospitalized…
That being said, & also said by almost anyone here, do the maximum radius you can in any given space.
Learning what I saw today, I cannot consider a passenger line under 50" in HO Gauge for the motion & look I want to preserve. I may go to extremes, but, minimum is not a consideration for me now, even in streetcars…
Just a few thoughts…
Here is a suggestion, do like I did, draw out some Radii on a board or paper, & then set your cars on that… See how it looks to your eye, & then evaluate it.
Wish the best of luck!!!
The answer is about 6" in HO. That assumes that the tracks will be side by side AFTER turning around. So a larger area at each end would allow this. One 4’ x 8’ plywood cut into two 4’ x 4’ pieces should allow approximately 22" radius curves on the ends.