I’d like some tips/hints on how to build a helix (in N-scale) to link 2 decks about 16" apart. I’m planning on a 3% max grade, and a turning radius of about 12.5 to 12.75" in the helix. How do I support each level of the helix ? How do I calculate how many turns I’ll need to reach the next level ? thanks
There is a good article in Model Railroad Craftsman in the December issue…talks about using octagonal sections of plywood instead of cutting curved pieces. I think I’ll foloow this general idea for my 180 degree turn on the end of my planned island. It’s just so simple! Good luck!
To calculate:
First, you have to determine the circumference, which is Pi times diameter. So for a 12.5" radius, that would be 25" x 3.14 = 78.5". Then multiply that by the grade, which in this case is 3%, or 0.03 x 78.5 = 2.355 inches of rise for every turn.
When you are designing such a helix, the tighter the curve, the more resistance on the train, which adds to how hard engines need to pull up a grade. What that means is that an engine will be able to pull a train easier up a 15" helix with a 3% grade than a 12" helix with a 3% grade. And 3% can be a pretty stiff grade to begin with. It is well worth the “investment in space” to make the helix radius as large as practical.
There are many many ways to support each level of a helix. One example would be to build the helix out of 3/8" plywood (which would still give you appox. 2" of clearance between levels in this case), and use 2" blocks of wood between each level of helix on each side of the track(s), spaced in 60 degree increments (which is six around one complete turn). Another example would be to the same 3/8" plywood, and instead of blocks, use threaded rods that run vertically (which will allow for more access to the helix). Drill holes on either side of track on the helix subroadbed, and nuts above and below the subroadbed to get the right height. This method will also allow you to adjust the height of each connection to get get most consistent grade (VERY important). There are many other methods, suited to each person. Please search this site and others for more ideas and experience.
Another idea to think about would also be to super-elevate those helix tracks, just a little.
—jps
Do you mean something like this, of course a lot smaller.
This is O, and the helix is 10’ in diameter.
The secret is that the radius and resulting grade percentage are linked. For N scale each turn must gain at least 2" measured from railhead to railhead. Doing the math, it looks like your grade expectation is in the right ballpark for that radius. 8 turns at 2" per turn will get you up 16". Increase the radius, and the grade comes down, as long as you maintain that 2" spacing. Increase the spacing, and the grade goes back up.
Bingo! That looks a LOT stronger than what this article talked about, but the concept is correct. This author was using plywood sheets and cutting out the octogon sides then using splices to link the multiple levels…I really like the idea.
Yeah Wes, but it has to be stronger, it has some real weight. I did the roadbed a little differently. There are actually 2 sets of 16 trapizoidal segments per circle. The total roadbed thickness is 3/4", but I laminated 3/8" CD and BC plywood together in a half lap pattern. I trimmed the excess as I went.
See that thing hanging down in the lower photo? That’s my compass, I secured a piece of conduit to form the center of the circle. An eyebolt allows the arm to move freely. It worked great, but is probably overkill for most modelers.
Big-Boy could build a 2 bedroom condo in that monstrosity. 
I’ve seen a similar article in another magazine where someone was able to make a much more efficient use of a 4x8 by cutting the helix pieces in thirds or quarters. IIRC, in that article, he used straight peices of that plywood for the vertical supports. He basically calculated the distance between levels, and cut slots in the vertical supports that the subroadbed fit into. He then used the vertical supports at the joints between the segments. That way, he didn’t have to have another piece of wood above or below the subroadbed for a splice, which gave more clearance.
—jps
Over on the Atlas N Scale forum, there’s a really good thread on the subject. The thread title is “PRACTICAL HELIX ADVICE”
Just a word of warning to anyone using the Railroad Model Craftsman magazine article for a reference to build a 30" radius helix. The author did not follow jschuknecht’s formula. The 30" radius curve translated into a 30" diameter curve instead of a 60" diameter curve.