Minimum radius curves and the reason to avoid them...

Model Railroader Layouts and layout building
1

Hi all, I just had a few thoughts that I would like to share.

The previous layouts I´ve had, have been in HO scale and mostly on the smallish side and I had tricked myself every time that I needed as many spurs as possible and that on the smallest area possible.

It is an equation that doesn´t really work.especially when you start to barter with yourself regarding the radii you will have, I settled mostly for 18", and that wasn´t always so smart.

The problems all came one after one other. Locos derailing, cars derailing, unable to operate anything longer than a 50´car… and worst of all, a nightmare to operate on as it was so cramped.

I felt the need to start on new layouts as I grew tired on the recent ones…The plans for a “better” layout is always in the works, right?

In the end I got an epiphany when I built a model railroad for the local museum, there it was spacious and I was to make it with lots of landscape and a minimum radius of 30". What a difference!

I scrapped my layout at home and started on a shelf layout instead, no more sharp curves. no turnouts smaller than a # 5 and a trackplan that is possible to expand in the future if I would wish. The space exists as a shelf layout is much more space saving than a roundy.round layout.

Now I can buy all the equipment I like as the layout doesn´t set the boundaries, only the era I´m modeling [:D].

It really makes the hobby (and the layout) much more enjoyable to me, as I don´t have to worry about what I can´t do but instead of what I can do.

So if you are in the position of planning a new layout. Avoid the small radius curves and tight turnouts. Plan for the future and I will promise you that it will provide you with benefits.

Hope it helps someone [;)].

2

[:)]

Yea, verily.

I had some 18-inchers on my previous HO layout. Ultimately, I found out that it is very difficult to lay a perfect 18-inch curve with flex track. I investigated by using a truck with an indicator made of a 12-inch piece of thin balsa wood (about as thick as two pieces of wire in parallel) glued cross-wise to the truck. As I moved the truck along the curve, the indicator revealed several places where the radius varied considerably.

The indicator should point to the spot on the layout that is the center of the curve. Where it points ahead of that spot, it indicates a local radius greater than intended. Where it points behind, it reveals a local radius less than intended. These tiny variations in radius were very difficult to see until after my tool pointed them out. Every problem I had with derailing on the supposedly 18-inch radius curves was at one of the locations that the tool revealed.

I toyed with the idea of using sectional track, but then we moved to a different house where I have much more room. My answer is the same as yours - change to a radius significantly larger than the “minimum” for your rolling stock.

[:)] [:)]

3

That’s why my next layout will use 60 - inch as the minium and # 10 turnouts wherever possible, might have to compromise and use # 8’s at industrial locations.

Dave

4

With that minimum radius there is no danger of derailments due to that at least, I even think that high speed reversing a long train through the # 10 turnouts won´t be a problem.

5

whatever radius you settle on, don’t forget the easements. even a short easement is better than none at all and you can compromise on the curve radius a bit to fit them in and still be ahead in the game.

in the real world we were always gun shy about shoving a long, heavy train backwards, especially through a crossover. too many times things folded up like Lawrence Welk’s accordian. thanka you boysa.

grizlump

6

Words that should be carved in jade and filled with gold! An easement can be the difference between silky operation and a burlap sackful of problems.

My test for newly laid track, whether it be a perfect tangent or a puzzle palace of double slip switches, is to back my designated derailment test train through it at 2x track speed. If it makes it, I’m good to go. If it doesn’t, the problem is isolated and fixed NOW. Good enough - isnt (Unless you set good enough as the closest possible approach to perfection.)

My solution to the minimum radius question was to erect a test spiral and run everything into it until the ‘not past here’ point was located. Then I eased the radius to something I was sure everything could live with. Of course, not every car can handle certain routes. Everything I own is happy on 610mm radius curves, but only those items that were good down to 300mm will ever be allowed onto the railed goat trail that leads uphill to my collieries. Actual minimum radius is 350mm, too tight for most of my mainline power, my longer freight cars and all of my DMU. But then, there’s no reason for any of those to be on that stretch of rail anyway.

On the visible part of the main curves will be wider - for looks, not for operating capacity.

As for overloading the bowl of spaghetti - more than one of my earlier layouts had more, and more complex, trackwork in less space than I’ve designe

7

[:)]

I use easements everywhere, but I have to be careful to allow for the extra distance between the tangent tracks that they require. For example, if I use an 18-inch radius, 180-degree half loop with easements, my two tangent tracks will be separated by 18 x 2 inches plus the easements (typically 1/2 inch each), for a total of 37 inches.

Looking at it the other way, if I plan the tangent tracks first, the curve connecting them will be a bit sharper with easements than without them. If I am not working with radii near the minimum, the difference is not important. This should be the case for the radii mentioned above.

[:)] [:)]

8

You couldn’t be more right on the money, yes a lot of locomotive manufactures advertise their engines can run on 18" curves sure they can and they look hideous while doing it and you will have to set sign post signals and utility pols so far back when your articulated go around the 18" bends so they don’t get wiped out. A lot of guys fail to understand the word “minimum” in my interpretation it’s just enough to get by. So unless your only running maybe a small consolidation locomotive and such 18" radius curves are a no no.

9

Couldn’t agree more with the OP.

Sadly, a lot of beginners getting into this hobby, including me seven years ago, are unaware of the real world requirements for smooth and flawless operation. An 18" radius may be possible with a switcher engine and 40’ freight cars but even then derailments are a distinct possibility if anything less than #6 turnouts are used. This is not to mention track work and the problems caused by humps, kinks and other associated track laying problems.

Now on my 3rd layout and planning a 4th, my basic rules are flex track only, 30" minimum radius, easements for sure, and disciplined testing of all track from the outset.

Yeah, I know, a lot of modelers have limited space to plan a layout. Well, sorry to say, if HO scale is going to be used, you are going to be disappointed trying to run much of anything on 18" radius, or 22" or 24" for that matter, #4 turnouts, and sectional track.

Just my opinion based on a lot of negative experience before I got smart.

Rich

10

At the same time, you need to be realistic and manage your expectations. I started with a 5x12 table layout, and I’ve incorporated that into the larger plan now under construction. I’ve gone to using longer turnouts, where possible, but since I was already using 18-inch curves, I saw no reason to avoid them.

Yes, it is difficult to get a good 18-inch curve with flex track. But, with a bit of perserverence, it can be done. I use a gauge, and I also pre-measure the curve and lay the roadbed using sectional track, so that the flex will pretty much do what I want when I lay it down. But, when you think about it, it’s just as difficult to lay a perfect 30-inch curve. It’s just that if you dip down to 28 inches somewhere, you won’t derail. If that 18-inch curve gets down to 16, you’re going to have trouble.

I grew up in the Transition Era, and that’s what I model. So, I have mostly 40-foot cars and 4-axle diesels. I’ve selected short passenger coaches that can just barely deal with the curves, but by taking care with the trackwork and turnouts, I can run them reliably all day long.

11

Make mine another vote for the road less traveled.

18" radius became the defacto HO standard back in the 1950s. Both because it fit well on a 4x8, and because the prototypes for most models were a lot smaller. 40ft and 36ft freight cars were the norm, as were 4 axle diesels (E’s and PA’s excepted). For those who wanted passenger car operation, several manufacturers made shorties to take the 18" curves. While big steam was available, it was accepted and known that big steam models didn’t run on 18" radius curves. The Mantua Mikado was about the biggest anybody expected on a 4x8 with 18" radius. IIRC, the Bowser Challenger was the 1st to break the understood rules.

Go back further to the 19th Century, and things are even better. Freight cars were commonly in the 28ft - 34ft range. The 2-8-0 was the standard big power on the grades in the mountainous West. In flatter areas, the 4-4-0s and 4-6-0s could pull passengers at higher speeds. A 65ft turntable (9" in HO) suffices.

12

Minimum radius depends on the engines. Brass engines with rigid frame need a bigger radius. I think, with more than 36’’ you’re on the safe side.

I’ve tested the radii for my narrow gauge start with a test track and my friend’s engines.

Wolfgang

13

Can you tell me what a easement is and if you can show me one.Dont understand how one works.Thanks.

14

I guess the title really shoudl be “Too small a minimum radius and why to avoid it”. If you set you minimum radius to somethign your equipment can easily handle, there’s no real reason to avoid having curves of that radius. I set mine to 24" because all the stuff I run comfortably handles that radius, and I have no problem makign curves that small. Just no smaller - that’s the whole point of it being a ‘minimum’ radius. Nothing smaller, but larger is ok where it fits.

–Randy

15

[:)]

An easement is a transition section between a curve with a fixed radius and straight (tangent) track. The actual radius in the transition section is not fixed, but varies smoothly from the radius of the curve to a very large or infinite radius where it joins the tangent track. The point of having an easement is to avoid running a train directly from straight track onto a curve at a single point on the track. The train can “ease” into and out of the curve.

Sectional track does not have easements. One plugs a straight section into a curved section, and there is no smooth transition.

If you do a search in these forums on “easement” you will see a wealth of information from people much smarter than I am about it, as well as many proposed methods of laying them on model RRs. I prefer the simplest method.

My comment referred to the fact that an easement requires a lateral displacement of the track that a connection without an easement does not need. Imagine a semicircle of sectional track with a 20-inch radius joining two straight portions to make a “U.” For purposes of this example imagine that the curve consists of six sections of 20-inch radius and that each straight portion consists of three straight sections.

The centerlines of the straight portions will be 2 x 20 = 40 inches apart. In order to make an easement one has either to reduce the radius of the semicircle by a small amount or to move the straight portions of the track farther to the outside by a small amount.

So, imagine at one of the transition points lifting up and removing one curved section (of sectional track) and one straight section without disturbing the placements of the remaining sections. Then move the entire straight portion a small amount towa

16

Just a bit of an opinion. Maybe worthwhile, maybe not.

Each of us has a certain amount of space to work with. We have to fit the best compromise between what we’d like to have and what we have available. And if we give up trying to build something we’d like to do because someone else says that’s the wrong way to go, we may never achieve a reasonable degree of satisfaction.

I have a 9’ X 13’ room that I’m looking at right now. That means a table about 6 X 13 with two sides against walls maximum. I’ve read that I’d be better off with an around the walls layout. Certain features of the room prevent that. The rolling stock I’ve collected, much of it scratch or kit bashed, often requires at least a 24" radius (HO), so I’m planning on 26" main. Transitions? probably not. Shelf switching layout? Possible option, but I’ve built a few, and while there’s a certain satisfaction, there are still times I want to watch one of my articulateds just running free. Can’t do that with a point to point shelf. same with the multi-truck flat cars and articulated passenger cars I have.

N scale to get the decent radii curves? I’m a 66 year old stroke survivor. I am about to sell my collection of N. Too small any more for me to work with.

Probably the most derailment free pike I’ve ever built in HO was a 4’ X 6’ L, using 15" curves and snap switches. That was in the days of oversize flanges, Mantua loop-hook couplers, mostly 40’ freight cars, and Globe (original Athearn) passenger cars. Even my first Mantua 2-8-2 kit loco could squeeze around on slow speeds.

You can look at the pictures of these super size works of art in the mags, you can drool over the fantastic work some people have done, you can wish for the room for a 30’ X 50’ layout, but in the end, you have your own situation, and you have to d

17

I try for 22" but 18" works fine (everything I run is 40’ or less) and #4’s have not been a problem but I try to go #6. The key is how good is your trackwork and you need to tune all your switches.

18

The flanges do make a difference. I find my 40’ cars in S have no problem with 19" radius curve (equivalent to about 14" in HO) with the hi rail flanges, but derail frequently with scale flanges. On a 24" radius curve they both work fine. I’m going with scale because I have the room for a minimum 33" radius curve, but if I were tight on space I’d use the hi rail.

Enjoy

Paul

19

Just curious. I’m trying to picture how to fit in a 6 x 13 foot table in a 9x13 foor room in such a way that it has two sides against walls, and I am not quite able to picture it in my head.

I assume your 6x13 foot table is not orientented in a 9x13 feet room in such a way that you will have to crawl on the floor under 6 feet of layout to get from one 18" wide aisle to another 18" wide aisle?

I also suspect that the answer may have something to do with how you use the word “room”.

Smile,
Stein

20

That’s a 9’ X 13’ floor space in a 9’ X 24’ semi finished basement area. A layout would be built against the outer concrete block walls, leaving me a 3’ aisle to a divider wall to the laundry/furnace/pantry area. The other end would open onto a small bar and general entertainment area. 18" aisles would be a little tight, especially for the access to the furnace combustion area and a small closet.

And, I remember the hoopla about the RP-25 flange contour promising to reduce derailments.

I guess I could have stated it better.

I think my original point is still valid: do the best you can in the space you have available. If you can’t do it “right”, do it the way that works best for you. Long as you have fun doing it.