curve radii question

[Anonymous]

When planning the radii, such as an 18" radius, where exactly is the radius measured?

18" to the inner rail, middle of the track or the outer rail?

[Big_Boy_4005]

Track center. When using flex track, just draw a line where you want the track to go, and keep that line under the center of the track.

[Anonymous]

perfect, thanks Big Boy.

hehehe that sounds pretty funny[:)]

[cacole]

If you're modeling in HO scale, you may regret having a radius of 18" later on if you ever try to run a passenger train or other modern-day rolling stock. You should try to use nothing smaller than 22" radius if possible.

[cwclark]

[#ditto]..yep..cacole is right...I just tore down a layout with 15" and 18" radius curves..couldn't run any loco more than an SD or a u-boat..and the passenger cars went around it so tightly that there were derailments constantly...22" radius is minimum...in fact..i won't go under 24" on my new layout....Chuck[:D]

[Anonymous]

I'll second those advices - don't go with 18" radius - you'll end up abandoning this hobby (I almost did) or replacing the track to higher radius.
I went with 24" Atlas code 70 rail and wish I did from start.
Oh, one more thing - make sure to get Nickel-Silver rails, otherwise, just like with wrong radius you'll have more frustrations than enjoyment.

[mcouvillion]

For those thinking of building a new layout, consider building radius templates first. I build a series of templates using John Anderson's technique for laying out transition spirals, but I laid them out on a single piece of luaun plywood. The templates were at 3 inch intervals from 21" through 45" radius, with transition spirals. (Each template is composed of the smaller and larger radius at each three-inch interval, so effectively you get two of all except the smallest and the largest.) Once everything was laid out on the 4x8 sheet of 1/4" plywood, I labeled all the templates with a permanent marker, (tangent, beginning of spiral, begining of arc of curve, every 11 degrees through the curve, 45 degrees (center of curve)) then got out the saber saw. It is extremely easy to "fit" a nice radius, usually larger than you would ever dream of being able to use, when you use a template. [For those in the Houston area, you can rent these templates through Papa Ben's.] When our club laid out the track plan for our sectional layout, almost everyone picked the 45" radius for the curves on their modules. I was surprised that no one wanted anything smaller.

We also included super elevation when we laid the track, using 1/4" wide strips of masking tape under the outside rail. We started with two layers of tape about 1 foot before the curve (still in the tangent, then went to four layers of tape at the start of the transition spiral, then 7 layers of tape at the beginning of the arc of the curve. Tape was applied through the corresponding location on the other end of the curve. The effect is subtle but noticeable. We had to guess how to do the super elevation because we hadn't seen any articles of how to go about it. I had seen one layout with a 4-track NYC main and the effect was awesome, but we weren't able to get any info on how to do it. The masking tape works well, is easy to use, and is cheap. Cut it on a piece of glass with a metal rule and sharp hobby knife.

When in doubt, always go with the largest radius possible.

Mark C.

[Big_Boy_4005]

Actually, I use a piece of heavy gauge metal strapping that has predrilled holes at 1" intervals as a compass. Works great. If you want to do transitions, a simple offset from the radius works well.

[mcouvillion]

To use the bar with the holes to construct the radius, you must locate the axis of the circle - not always an easy thing to do since it usually is not on the benchwork but in the aisle. With a template, you just lay it on the benchwork or on the future roadbed, align the tangents, make sure the curve doesn't interfere with anything, and then draw your centerline. Takes a minute to do. If you don't like what you get, swap out to a different radius, re-align, and draw the centerline. Takes another minute to do. You can't begin to get set up and aligned in anywhere near that time. (I did use the bar with holes to construct the template layout.)

It took about three hours to set up the template layout and another hour or two to cut them out and sand them. It is very easy to select the appropriate radius from the series of templates to fit any corner.

Mark C.

[Anonymous]

I differ with many folks opinion here.

Yes, 22", 24" or higher radius is great. Yes, you have more flexibility in what you can run. HOWEVER, in the real world a lot of us face the choice of 18" or nuthin'... If it's a choice between a layout in limited space where 18" is the only way you'll get anything but a "snooze-o-rama" loop, then by all means go to 18". Just DO be aware of the limitations - you'll be much happier running an American 4-4-0 and old-fashioned shorty cars than trying to make 18" and an articulated loco with 80' passenger cars make nice. But there are many options you STILL DO have with 18".

Another option in limited space is drop to N gauge or lower. Personally I find it unsatisfying, and have too much investment in HO rolling stock to change now. But it is an option - especially if you have little space AND are starting from scratch.

So yes, go with 22" or even more if you can. If you cannot, don't shrug and walk away. Go with the 18", make sure you don't try to run what you shouldn't, and have a blast!

[Paul Milenkovic]

Tell me I am crazy, but I am planning a layout for HO to go into a 24" by 34" TV hutch that will use 9" radius. I plan to run shorty 25' ore cars and something like a Porter Hustler or an 0-4-0 steam engine. The plan is to have some kind of industrial/mining theme.

Your minimum radius is determined by the kind of equipment you are going to run -- personally I think that 30" in HO is the minimum for 85' passenger cars and the newer 6-axle Diesels. But if you are tight on space, you can model a tight-space railroad.

On the subject of passenger cars, there is always the Talgo, which has 40 foot cars. There is a commercial Talgo model that steers the axles with springs -- I have built a 3-car Talgo that steers the axles with linkwork on the rooftop (couldn't get the prototype side-mounted axle-steering links built, but the rooftop links are way cool because you can watch them in turns, a little bit like watching the valve gear on a steamer. Besides, the prototype always sticks stuff on the roof that they can't fit under the car -- RDC radiators, those blisters on top of the Acela cars, air tanks on top of SD-24s). That Talgo model works just great on 18" radius -- it seems to run smoother than conventional-trucked cars.

Oh, and transitions curves are a must -- John Armstrong has this thing where 18" with transitions is better than 24" inch without in the "lurch factor" department. And you can do transition curves in snap track -- get your self a template and snip the plastic between ties on the side you want to expand -- this technique was described somewhere else on this forum.

[sully57]

Wish I checked in with all of you regarding radii before I layed track. So, to lend my recent experience to tondogg. I just finished laying track on an HO 5'x9' layout. No scenery yet. 4 turnouts. Using 18" mainline, and 15" secondary radii. All code 83. Started running trains, to see how things are to this point. I am half-tempted to rip it all up, and start again. Exeriencing myriads of probs with derailments. Some cars/locos will work ok, others have problems. I just haven't been able to consistently resolve them all. The more I read, the more I realize that doing something greater than 18" radius would probably have been the smarter approach. I just have no faith that this will all run well, as is, once it's all together. I am discouraged with moving onto anything else (scenery, converting to DCC etc.) untill I resolve this radii issue.

[egmurphy]

Well we've moved a bit away from the original question, but that's okay. And, based on earlier posts, I think the original poster is going with N scale because he is space limited. Which means he'll probably be looking at 9-3/4" and 11" curves (the rough N equivalent of 15" and 18" in HO).

Sure wider curves would be better, I'd love to have them myself. Unfortunately using anything wider would limit me (and a lot of others) to a simple oval. I'd like to say that you can build a layout with good operating trackwork using 9-3/4" and 11" (15"/ 18") curves, you just have to take care to do a good job installing it, being especially careful of the alignment between adjacent pieces.

And, as already pointed out, equipment needs to be selected with the limitations of your curves in mind. Four axle diesels and 40' or 50' cars do a lot better on tight curves than SD70MAC's and autoracks.

So while I'll second the advice that "wide curves are always better", I'd add "if you have the space to use them". But I don't think that we should give people the idea that just because they have to use the smallest available radius curves that they can't build a satisfactory layout.

jmho

Your mileage (and curve radius) may vary,

Ed

[Anonymous]

Thanks everyone for all of your thoughts.

I am going with N scale, perhaps I should have mentioned this. I appreciate the responses and advice, which is most valuable to a beginner like myself[:I]

[Paul Milenkovic]

About all of those derailment problems:

Don't know if I would blame them all on the radius of the curves. I would check:

1) I guess they don't sell stuff with horn hook couplers, but if you have them, they put a lot of sideways force on cars, more so when backing up.

2) Checked wheels, track for out of gauge? Trucks for binding (restricted from pivoting)? Checked wheels for dirt or out-of-round from gunk on them?

3) So-called talgo couplers (truck mounted couplers) are especially a problem when backing, can be a problem when mixed with cars with body-mounted couplers. Is this irony or what? My Talgo model is semi-permanently (pretty permanently - it is a big disassembly job) coupled at the shared axles, but it has Kadee couplers at the ends to hook up to a locomotive. I built it with a "talgo coupler" -- i.e. a coupler attached to a guided axle on an end car, and I had derailment problems through switches. Changing to a body mounted coupler and the trainset (jargon for a semi-permanently coupled group of passenger cars) works fine.

4) Interactions between Atlas code 83 turnouts and certain rolling stock. I had a terrible time with the lead truck of a Bachmann 2-8-2 steam loco (I am modelling a modern era, but the steamer is for railfan excursions) started jumping the tracks everytime at the same place. It seems that the radial truck for the lead axle is steered at an angle through a change in curves (have the same situation with the steered end axles on the Talgo trainset), and if it hits the notch in the rail that the point mates into, that lead truck will jump the rail. It is not "picking the switch" -- it happens in the opposite direction to where you think it will pick the points of the switch.

A little action with a needle file to round down that notch in the rails fixed the problem with the steamer. Anyone know what I am talking about on the Atlas Code 83 number 4 turnout?

5) Are any of the cars/locos light weight? Not enough weight makes rolling stock susceptible to jumping the tracks.

My advice is not to pull up your track and start over again -- any layout, even the new one after you start over, can have derailment problems. Don't blame everything on the track -- it can be your rolling stock and couplers. Think of the total system of the track and rolling stock as a machine mechanism and trouble shoot that mechanism for its failure modes.

I would only pull up the track if I don't like to look of the layout or the look of the equipment on it -- try the other troubleshooting procedures before you get discouraged and decide to start over. You can redo your whole layout out of "radius envy" and find you are still having derailment problems because the fault is in the rolling stock or your Atlas switches need some tinkering with a needle file.

[camarokid]

re: sully57. If at all possible use 18 and 22 " radius track sections back to back starting with the 18" section through the curve. I have an FP45 that derailed on 18" curves and sometimes on the 22" believe it or not. I tried the above solution and found I could run a whole lot of stuff through this curve. I am now on my 6th layout and unfortunately I still have a tight corner where this curve arrangement is still used and I have no problem with 6-axle diesels or my Big Boy . Hope this helps and works out for you.

[sully57]

thanks Camarokid!