I have a 15'' radius curve on my layout and I can run a Dash-8 through it at top speed, with all my freight cars behind it (which is sadly, not very many freight cars), so why not have 17'' curves for a logging layout?
There's no reason not to go smaller if your equipment can handle it. Interestingly enough the NMRA RP for curves http://www.nmra.org/standards/sandrp/rp-11.html doesn't have a class for 18". They have one for 16.5" for up to 50' cars and 20" for up to 60'. 18" comes from track manufacturers and became the target radius for many manufacturers' large locomotives and long cars. But shorter ones should handle sub 18" just fine.
Enjoy
Paul
Thanks for the replies so far. Based on the feedback received, I'm going ahead with my plans for my tight radius curved switches, pending some test runs with my equipment on temporary 16-17" radius curves. I will let you know how things "turn out" (sorry about the pun).
Tom
canazar One word of warning. I admit, I run HO and mostly either steam era or modern day freight stock. One draw back to tight curves is over hang from the cars or, more importantly, the engines. 2 inches of clearance is very, very tight for most equipment. I know I screwed myself in an area of my double track main where if I am not careful, the engines will touch cars depending what's rolling. I had done 2" centers and I need more. I think NMRA set the minimum at 2 1/4. But, with tighter tracks, the greater the overhang. Along witch checking the radius, make sure you watch how far out the engines swing or rolling stock. Sounds like you are running the rigth equipment, just hate to have a bump everytime you have a train in the siding.
One word of warning. I admit, I run HO and mostly either steam era or modern day freight stock.
One draw back to tight curves is over hang from the cars or, more importantly, the engines. 2 inches of clearance is very, very tight for most equipment. I know I screwed myself in an area of my double track main where if I am not careful, the engines will touch cars depending what's rolling.
I had done 2" centers and I need more. I think NMRA set the minimum at 2 1/4. But, with tighter tracks, the greater the overhang. Along witch checking the radius, make sure you watch how far out the engines swing or rolling stock. Sounds like you are running the rigth equipment, just hate to have a bump everytime you have a train in the siding.
I hear ya. When I tested my track center spacing before laying actual track (so I used cheap or old brass flex track) I found that with my proposed 40" and 38" radius curves on double track main line, I could use 2" centers on curves and still run trains with 85' passenger cars on both tracks with no interference, although it was darn close. When i tried to lower that to 1 3/4", it was no go. So I kept the 2" spacing (which I like visually because it can be uniform between tangents and curves) but to be safe I upped the curves to 42" and 40" radius. I realize not every can have those radius curves, and not everybody has a double track main. But most people would like to run full length passenger cars regardless of era, and if they model the modern era, the longer freight cars. Testing is the way to find out how low you can go.
Dave Nelson
I have recently been installing track in an industrial switching area. After putting down a section that has an s-curve, and using the standard of one car length of strait track between the curves, I found that the radii worked out to be around 15 inches. I thought that I would have to pull it all back up and figure out a new plan, but I found that a four axle deisel moving a couple of cars seems to negotiate the area without any problems. Using logging type equipment, you shouldn't have any problems with what you are attempting. As previously stated though, make sure you will have sufficient side clearance.
Looks aside, I just ran a couple of Hi-Cubes around my 4x8 layout (22" R) and was surprised they didn't derail! (The Hi-Cubes are for my new layout with 36" R min curves) If you're unsure, err on the safe side or, at least, make sure you can get to any potential problems easily (i.e. not in the back, or any other hard-to-reach places). Trackwork rarely gets better with time. Maybe ask others for alternate trackwork ideas to offer ideas you haven't thought of? On another idea...doesn't superelevating ease the radius a bit? Might not look right for a logging railroad though, but then again, it might not be that noticable?
http://delray1967.shutterfly.com/pictures/5
SEMI Free-Mo@groups.io
Best Regards, Big John
Kiva Valley Railway- Freelanced road in central Arizona. Visit the link to see my MR forum thread on The Building of the Whitton Branch on the Kiva Valley Railway
I believe Kato track has curved pieces of something like 16-3/4" radius, you could get a four pack of them and test run some stuff too.
Keep in mind that the sharpness of the turnout itself is determined by the frog angle, not the radius of the track after the switch. You could lay out a turnout with a no.5 or no.6 frog which would act as something of an easement going into the 17" radius curve...although as you mention this could limit the length of the siding.
At the risk of stating the obvious --- it should be a simple matter to pencil in curve radiuses of 15", 16", and 17" on a piece of plywood or heavy cardboard and curve a piece of flex track -- maybe using double sided tape, or thumb tacks, to temporarily lay the track to those curves -- and give it a try. I tested all sorts of curve and track spacing and ballasting method combinations in this way before laying final track. Of course as a geezer I had a large supply of old brass track for testing that I wasn't going to use on the layout anyway. Brass track is practically given away at swap meets.
Atlas makes 15" radius sectional track and on a previous layout, I used a few pieces of this on a tight industrial spur track. I wouldn't try it on the mainline but for what you plan, it should be OK. As long as you aren't going to run 6 axle diesels or freight cars over 40', a 17" inside curve shouldn't give you problems.
For a back woods logging railroad, 17" should be more than big enough, especially if that is the only section. I'd say that gaining the space between tracks is the big plus, taking care of any excess overhang you may end up with.
My main line has a 28" min raidius, and even that is a little tight for what I run there. But the interurban has a 9" (around the car barn) that I can get a motor and 1 40' car around. I ran into a space problem for the approach to the interurban interchange, so did a test with 15" radius. An SW type switcher can haul a few 40' reefers around that curve. Very tight and needs slow running, but a logging road should not go very fast anyway.
18" radius came from trying to get 2 parellel tracks onto a sheet of plywood. Many of the 4x8 plans have 15"R for interior tracks. I'd say go for the 17"R and ENJOY.
Phil
Timber Head Eastern Railroad "THE Railroad Through the Sierras"
Instead of different radii, why not use the same radius for both curves and connect them with 2.5 inches of tangent (which, if you handlay, can be converted into about a foot of spiral easement with a maximum 3/8" offset.) That way the outer track will balloon out from the inner track, adding a carlength or more to the length between clearance points at each end.
The big advantage of handlaid specialwork is that you, not the manufacturers, control the track geometry.
One thing to do, to test rolling stock tolerance for curves, is to lay a spiral of flex track on a piece of plywood. The MR staff did that back in the '50s, to check the accuracy of the current thinking on minimum radii. Most of the kitbuilt locos came in between 16 and 24 inches before derailing. The original Varney "Little Joe" Dockside got down to 2"! (I wonder if its present-day descendants can do as well.)
Chuck (Modeling Central Japan in September, 1964)
I'm close to finalizing my track plan, but there's one area that's still giving me fits. I'm trying to fit a short passing siding on to the 6-foot side of a short turnback peninsula. While trying to balance multiple space-related constraints, the best I've been able to come up with so far is a pair of 20"/18" radius curved turnouts (that I plan to hand lay) on either end, which still allow for only a 2" spacing between the parallel tracks. I am concerned that the "shallow" nature of such turnouts will suck up a lot of car lengths (right now only 6 car lengths will fit on the proposed siding). The layout is based on a backwoods logging railroad, so short trains are already planned for, but a locomotive, tender, caboose and three cars would be extremely short. I did try for 22"/18" turnouts, but they didn't fit due to some of my other constraints.
Then it hit me that maybe I could get by with two 20"/17" turnouts. I laid this out on my CAD system, and found that it would lengthen my siding to 8 or 9 car lengths (much better), and the spacing between the parallel tracks would be between 2.5 to 3 inches. I know that typically, 18" is the minimum desirable radius for operation, but considering that I am running only short wheelbase locomotives and cars, and considering that trains will not enter the siding quickly or frequently, I wonder if this isn't the solution to my problems.
Any thoughts from other layout builders that have tried curves less that 18" radius? Have they worked out for you, or do the disadvantages outweigh the advantages in your experience? I guess one obvious answer would be to lay out a temporary 17" radius curve and run some equipment on it. Still, I'd like to hear any opinions based on experience.
Thanks in advance,