If I want to use a 22* track on the inside of a double track curve would I use a 24* for the outside track? or would it need to be 26*?
GS
It depends on the scale and type of equipment one’s using. If in HO, you may want a separation of 2 and 5/16 inches between centerlines.
http://www.nmra.org/standards/sandrp/s-8.html
Mark
hi
from 102 Realistic Track Plans page 17:(Andy Sperandeo) and Track Planning For Realistic Operation (John Armstrong), both for HO
radius = 18", track spacing = 2.375
radius = 24", track spacing = 2.250
An advice by John Armstrong: If you don’t add a margin; best determined by experiment, you may have to restrict yourself to …
When you are dreaming about Big Boys pulling 89-feet autoracks you just have to set it up.
Paul
I’ll be modeling HO and SD 40’s and grain and coal hoppers will be running
if you want them side by side use the same radius. 22"
26 would be rather broad while 24 would be a bit close (given the 21/4 inch recommended spacing) and would have the cork or other standard roadbed touching. I would be nice if Atlas sectional came in 241/2 radius but it doesn’t.
Paul (Paulus Jas) had it right, set up your curves and pull a short train through the inner curve with cars on the outer. Nothing like direct experience.
Happy Holidays
Alan
You have touched on one of my major sources of heartburn. Sectional track curves are manufactured in two inch increments, which makes for either a too-tight clearance or a huge waste of space.
My own standards (based on rolling stock with a 250mm maximum length) call for 60mm clearance, minimum radius 610mm (24 inches.) Every track manufacturer in the business can provide me with 24 inch radius sections. NOBODY manufactures 670mm radius sections.
The solution, of course, is to use flex track, and lay whatever radius you think you need. You can also incorporate spiral easements, which vastly improve operation over any curve radius.
Addressing the original question, if the inner radius is fixed at 22 inches (560mm) the outer radius should be 620mm (24 5/16 inches) - another radius nobody manufactures.
Chuck (Modeling Central Japan in September, 1964)
Test, test, then test it again. It’s the only way to truly KNOW. You need to test various combinations of cars, and look for both the ends of the cars on the inner track interfering with cars on the outer track, and the centers of the cars on the outer track interfering with cars on the inner track, You’d think that with 32" radius on the inner curve, 34" would be enough on the outer. Luckily, I tested it first. The worst offenders were NOT the out-of-era giant hi-cube cars (used to test paints and track overhang), either. So don’t skimp and just test your longest cars.
–Randy
“if you want them side by side use the same radius. 22”
Makes perfectly good sense to me why wouldn’t you just move the center of the 22" radius inward 2-1/2" and keep both tracks at the same radius? it your inner and outer radius’s are different isn’t that going to cause a problem once you come out of the curve into a straight run or am I missing something here?
Makes perfectly good sense - for curves of 90 degrees of arc or less - and there will still be overhang issues at the places where the curves become tangents unless the 2.5 inch spacing is to be continued everywhere.
However, the OP never said how many degrees of arc he’s looking at. My own layout has more than a few concentric curves of >180> degrees of arc, and the radii, of necessity, are not the same. I assumed, for discussion’s sake, that the concentric curves might be the turnback at the end of a peninsula, or perhaps for double staging tracks around a hidden reverse loop. Neither is conducive to simply offsetting curves of the same radius.
I agree with Randy that the best way to check for overhang interference is to test-lay the intended track geometry and run the things that might be unhappy on concentric tracks. An ounce of experiment is worth ten tons of opinion.
Chuck (Modeling Central Japan in September, 1964)
Chuck,
Kato UniTrack comes in 550mm, 610mm, 670mm, 730mm and 790mm radius. I used the 670mm on my Christmas tree layout (see picture at http://cs.trains.com/trccs/forums/p/165215/1820711.aspx#1820711 ).
Alan
Only if you at a straight section in the outer loop to increase the overall diameter, otherwise the track will intersect. (Did you mean 24in radius?)
Hi!
May I echo those that said “test, test, test”… I’m also building an HO layout with a double main and a third inside track that in places looks like a third main. While I had everything drawn on paper (in scale), I realized that even the best of plans can sometimes hit a glich when they are put to work.
I started with the outside main, whose curves ranged from 29 to 30 inches. I experimented with clearances before I put in the inner main, and 2 1/2 worked out just fine. Remember, when testing to have your longer cars & locos on BOTH tracks to check for clearances. Sometimes our curves are not constant radii and the right combination of rail cars and timing will create a screeching crash.
I finally settled on a 2 1/2 inch spacing, which works just fine. Of course, with larger radius curves you can space parallel tracks closer together, but with smaller radius they have to be further apart.
Oh, one last word of advice from a “been there, done that” kind of guy… “assume NOTHING” when it comes to laying track or wiring. Testing is the only way to be sure…
Mobilman44
Good to know as that is the spacing I decided on from the get go (will be running 85ft passenger cars - of course the 20th Century Observation Car won’t run on 28" radii due to a modeling flaw - the rear car body steps block the truck, they come off easily tho).
[:O][:I][#oops]
To be honest, I never even checked Kato’s UniTrack specifications - because I never considered the possibility of using it (or any other sectional track on roadbed.) Nice to know that somebody there, working with the same (prototype and scale) equipment I run, reached the same conclusion that I did.[^]
Now all we have to do is convince Kato to provide us with proper spiral easements…[:-^]
Chuck (Modeling Central Japan in September, 1964)
Only Kato?
Actually, Atlas already provides me with spiral easements of several geometries. I lay them with flex track.
To change parallel tangent tracks on 50mm centers to concentric curves on 60mm centers I provide the inner track with an easement that has 20mm offset and a total length of about 800mm. The outer track gets 10 mm offset and a total length of 500mm. No lateral interference, and silky-smooth appearance as a 6-car DMU train meets a freight consisting of auto racks, long reefers and JNR 20-meter container cars.
Chuck (Modeling Central Japan in September, 1964)
Chuck
I agree that generally when ever you can lay track down temporarily for test purposes it’s a good insurance that things will run smoothly but if the NMRA standard for a double track mainline is 2-1/2" then why wouldn’t it be the same throughout the entire mainline? I can understand if there is something like a passing siding or a siding that may run parallel to the main for a brief distance until it heads of so to speak in the direction of an intended industry or such but wouldn’t the st
I had the same issue myself, and I have seen the response posted already, but I’ll tos my 2 cents anyway.
If you’re running 40-2’s with 55ft centerflows and misc. hoppers on a 22 inch radiaus, my suggestion is go ALL flex track. Do what I did.
go buy yourself about 8 pieces of Atlas, etc 22 inch radius “Easy Trak”. Pick your brand, doesn’t matter. Use that as anothing more than a drafting line. Lay the easy-track, then draft around it with a pencil. Once you have your “22” inch route, then lay your roadbed and go to the outside using about 3/8ths of an inch space between roadbed slices. You’ll end up about 24 ish on your outside radius, and you’ll be pretty much equal all the way around. I use my 8 pieces of 22 inch easy trak as my “don’t go any tighter than this” mark. It’s easy, traceable, and gives you what you really need. ROADBED outlines, not track outlines. With a roadbed outline, you can lay the bed, then tack the flex roughly in the center and you’re Kosher.
From there, flex the whole thing, 22’s included.
Kato HO Unitrack has curves that work out to 19-1/4", 21-5/8", 24", 26-3/8", 28-3/4" and 31-1/8"radius, so allow 2-3/8" spacing for double or multiple-track curves.