I started building my new layout. I'm thinking of changing my plans by turning my curved section of a 3% grade into a tunnel. My outside track is at 24" radius and inside track at 22"radius which is 2" centerline to centerline. My portals would be on straight track on each end because someone told me don't put portals on a curved section because the cars my hit the sides. Will this work? I'd appreciate your feedback.
if you are working in HO scale you are going to need more that 2 inch track spacing for those curves. suggest you look at the clearance standards on the NMRA web site.
grizlump
You must be able to reach every inch of track inside your tunnels. Not only for problem resolution, but also for track cleaning Run your longest car through every inch of tunnel track before closing the tunnel up. Then run your longest train through every inch of tunnel track before closing the mountain up. It's a lot harder to fix design or track problems working through access holes after scenery is completed.
Dave
Lackawanna Route of the Phoebe Snow
The NMRA recommendations are the result of lots of thought and testing, and should be consulted.
A factor may be the size and era of your equipment. With small steamers and 36' or 40' cars of about 1910 era, the 2" centerline may work just fine. Even in that same era, if you are running full-length 85' Pullman cars, the amount of overhang on the curves will start to create a problem.
Most of the commercial tunnel portals have a little extra width over the NMRA standard which can allow for applications in difficult spots. Take care in positioning the portal - get an overhead view and roll your largest equipment through the area and carefully mark the position for the portal installation. Double-check it. My other comment on tunnel portals is that a railroad usually has the same style of portal throughout their line. Yes, there are exceptions, but having a wood tunnel portal, a cut-stone portal, and a cast concrete one on the same line would detract from the "company" image.
Good luck. Bill
The trouble with many tunnels on small layouts is that it appears the railroad went out of its way to tunnel the mountain rather than bypassing it with a detour only scale feet away. To be effective, the ends of the two portals should enter into different scenes or there is no apparent way the railroad could practically reach the different sides without the tunnel. For example, a railroad will tunnel through a rocky outcropping along a river.
Mark
markpierce The trouble with many tunnels on small layouts is that it appears the railroad went out of its way to tunnel the mountain rather than bypassing it with a detour only scale feet away. To be effective, the ends of the two portals should enter into different scenes or there is no apparent way the railroad could practically reach the different sides without the tunnel. For example, a railroad will tunnel through a rocky outcropping along a river. Mark
Agreed. If the object is to hide the turnback curve, a grove of trees or a multi-story building might be a better choice. OTOH, if the entire layout is set in mountainous terrain...
On my layout, tunnel portals serve two purposes:
The prototype I am (roughly) following runs up a steep-sided valley. The only reasonably flat spot on the route is the location of the main station (and they had to level a small hill and fill in the adjacent ravines to create it!) In that kind of terrain, tunnels are inevitable. In more level terrain, cuts or line shifts are much more common. Always remember, tunnels are expensive to build, expensive to maintain and sources of potential trouble - things which our prototypes would rather avoid if possible.
Chuck (Modeling mountainous Central Japan in September, 1964)
I agree that you will likely encounter problems with the tight clearances you describe, and not just in a tunnel. I would feel better adding even a full half-inch, if not three quarters for no other reason than you may actually want to run long passenger cars or auto racks along them, or both types of cars going in opposite directions along the nested curves at the same time! While you may be building what you think you need now, it wouldn't hurt to anticipate, and build capacity for, what may come later.
Having been there, I know that the heavy majority of us develop a yearning for bigger and longer stuff to run on our layouts. We model railroaders like to test things, and push the envelope.
Thank You all for the information. I'm going to start this project this weekend. Also, I would like to say this is the BEST Model Railroader forum, no matter what you ask, someone will have an answer or a suggestion.
I have a 15' x 20' layout with the same double track spacing as yours and with portals on the curved sections. First, the standard portal is too small. Next, the way I fixed this was to raise the portal about 1/2" to give better top clearance. Then I cut the portal in the middle and added a 1/2" piece between the two sections. This gave me plenty of clearance for everything.
By the way, I took my newly fabricated portal and made a rubber mold so I could make as many as I needed. Also, be careful if you add tunnels as these may also interfere when you use curved track.
Ron K
Hi!
On my recently torn down HO layout, I had a number of tunnels and each had unique portals. The one that was on a double track curve ended having two double track portals "kitbashed" into one longer to allow proper clearance.
I had the layout (11x15 two level) since the early '90s and it had 4 or 5 design flaws that finally caused me to take it all down and build a new one. Two of the "flaws" concerned tunnels. The first was that while I could reach inside them, I could not readily see the disposition of the three connected turnouts located in the biggest tunnel. I figured my light indicators would always keep me informed, but while they may have worked, the "operator" screwed up more than a few times. Getting "cute" with fancy trackwork in tunnels is not a good idea.
The other "flaw" was not so obvious to most folks, but to me it was. The one major tunnel complex was surrounded by flat areas in which a real railroad would have used, rather than tunneling through hard rock. If we are going to model a real railroad, that is something we need to keep in mind, for digging tunnels was an expensive proposition to be avoided if at all possible.
For what its worth......
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central