What Is The Minimum Radius for a Helix??

Discussion in 'N / Z Scale Model Trains' started by Hoss, Jan 2, 2004.

  1. Hoss

    Hoss Member

    I'm going to be putting a helix in my layout (see photos in sig) to go down to a hidden staging area underneath. What radius is a good radius for a helix? I can easily fit an 18" radius in now, but can go bigger if I make some adjustments to the benchwork. I anticipate the second deck being about 18" below the first. I think that would allow plenty of room to get to the trains.

  2. 60103

    60103 Pooh Bah

    The answer to any question about "minimum radius" is "as big as possible."
    I'm a little short on calculators right now, but you need to look at grades and length of a loop of track (22/7 * 18" * 2) and how far you need to drop in that distance. About 113". At 2% that gives you about 2 1/4". Is that enough? Will your locos pull a satisfactory train up 2%? Remember that the 2 1/4" is from railtop to railtop, you have track, roadbed, subroadbed to subtract from that. Plus "gefingerpoken" (as the sign says).
  3. Hoss

    Hoss Member

    I come up with the same numbers you do for an 18" curve on a 2% grade. Hmmmm....I could easily change the benchwork to allow for up to about 22" radius.

    By my calculations, that would be approximately 138" per "loop", dropping 2.875" per loop on a 2% grade. I think this would be mo' better. Take out a half inch for subroadbed (1/2" plywood) and then just say 1/4" for cork, ties and rail and that leaves a little over 2" clearance...which should clear the tallest N scale cars. Doesn't leave much room for finger pokin', but I think that's about the best it can get with what I have.
  4. Russ Bellinis

    Russ Bellinis Active Member

    You might want to eliminate the cork and lay the rails directly to the subroadbed. A helix, if you are not modeling Tehachapie or the Spiral tunnels is in hidden trackage, and you could probably use the extra clearance that eliminating cork would provide.
  5. SD90

    SD90 Active Member

    That's a good idea, and I would keep the radius as large as you can too. The more room you have to climb, the better!

  6. Hoss

    Hoss Member

    A 22" radius is the largest I can fit in, but I think that should suffice.

    Now...how do you make a helix? I was thinking of suspending it from the framing on the benchwork with some all thread and nuts located at the appropriate heights. But, do you just use the same plywood you would on the layout or is there a better way to do it? Seems like a waste of a lot of plywood just cutting 22" radius strips.

    Anyone have any good direction on how to make a helix? I know I can make it the way I'm thinking, but I'm wondering if someone else may have a better method.
  7. 60103

    60103 Pooh Bah

    Try making your strips running parallel down a sheet of plywood. You might get a 24" wide piece to start. Mark the centerline 12" in and mark a centrepoint 24" down from the top edge. Draw a 24", 22" and 20" curve from one edge of the plywood to the other. Also draw ends as straight lines from the center to the edge (no, draw them between the 20" and 24" arcs.
    Mark more centrepoints every 4" down the board and repeat the arcs. When you get halfway down, you might want to start working from the other edge.
    Cut on the 24" and 20" arcs. You may need to fiddle a little between the inside of one curve and the outside of the next -- you may be able to get away with just one cut.
    If you don't cut the square corners off the first pieces, you could use them for straight run-ins.
    (I gave specs for 4" wide roadbed; can be changed as you like.)
    Mount any splice pieces on the top of the plywood, outside the track.
  8. 60103

    60103 Pooh Bah

    I saw a suggestion for using wood strips with dados cut in them for suspending the subroadbed. They said to cut the dados at an angle to match the grade.
    I've seen the threaded rod used as well. Don't tighten the nuts all the way or you'll put level spots into your grade.
  9. fifer

    fifer Active Member


    Mine is 18" radius and about 2 1/2 " seperation and 4 turns , that get me up 9 3/4 " using all thread and plywood.
    I cut mine in 4 circles (2 sheets of plywood ) using no cork.

    Attached Files:

  10. marc gast

    marc gast Member

    Helix Hoss


    The first thing to consider is, what type of rolling stock, motive power and lenght/weight of trains you will be running. You need to remember that basically, a 1% grade robs you of at least 25% of your pulling power, plus you are negociating curves which robs you of even more pulling power. You should also decide how high you need to go, etc. A helix is great if you have the room, however, I prefer to see long runs up the mountains, etc. I am not a helix fan as I believe they take up more room than necessary. However, that is my oppinion. A 22 in radius is not bad in N scale and I would suggest no more than a 1.5% grade which would be a 1.80 inch rise with in a 120 inch lenght.
    This would be a 44 inch diameter circle which is approximately 100 inches of track (figure your guzintus-the Jethro Bodine method). Now take into consideration you need subsupport for the track, clearance between the levels of helix, etc. your grade becomes steeper. For N scale, I wouldn't think more than 1/4 inch plywood would be necessary unless you plan on taking a hike someday. Like Mike mentioned in the previous Thread, use Ready Rod, etc. to link the levels together. This way the levels are not permanent and can be adjusted.
    We all remember the cartoon Helix the Cat? LOL
    Hope this helps you out.
  11. Hoss

    Hoss Member

    Re: Helix Hoss

    Marc, again thank you for your comments.

    Let me clarify a little bit by showing the picture below and then following up with the clarification.


    The above is the track plan I have begun construction on. The maroon track you see towards the bottom...the one that disappears into a tunnel (or something)...will go to a helix that will go DOWN to a lower level used strictly for staging. If you look at the "stop sign" portion of the layout, the 22" radius helix will be directly beneath the lake and tracks in that location. In other words, it won't be taking up any room on the layout because it will be UNDER the layout. The heightest level of the helix is approximately 3.5" lower than the lowest mainline track in this location. Go HERE if you want to see the track elevations...but keep in mind the drawing at this link shows an 18" radius helix instead of a 22" radius (I was too lazy to change it and post it again).

    By my calculations, a 22" radius at a 2% grade will leave approximately 2-1/8" or so clearance if I use 1/2" plywood. This should be plenty of room for N scale. I will be dropping probably about 18"...maybe as much as 24"...to get down to the staging.

    The trains I will be running will probably be between 8' and 10' long in length. They will generally be powered by 2-3 Kato or Atlas 6 axle locos. I think the locos will pull the trains up the grade easy enough. I'm more worried about couplers letting go than anything else, but I guess we'll see what happens.

    Clear as mud??
  12. A possible 'easy way'?

    there is a company called 'Noch' that sells premade N-scale Helixes at 22.5" radius.

    Trainscape makes a similar product called 'Easy-Helix'

    these of course cost more money than building your own
  13. fifer

    fifer Active Member


    ScrewySquirrel has a very good point.
    If I had it to do over I think I would go with a pre-made.
    I had also thought about using Aurora or Tyco Model racecar track,but couldn't find enough for a little cash.
    If I were to do it again I would also consider Plexiglass.
    The splice plates on each loop have to be very thin, I used steel splice plates and screw's and roofing joiners on the edges.
  14. lock4244

    lock4244 Member

    When my father built our first n scale layout 16-17 years ago, his masterpiece was the double tracked helix. He claims it was built to 19" minimum radius on the inner track and 2% grade (I have never calculated either of these). The track was laid right on the plywood... no roadbed. It's about 3-1/2' to 3-3/4' across. The record I set was a 60 car train the the helix (filled roughly three turns), but typical was 30-40 car trains with 2-3 Kato 6 axles (SD40 & U30C). Funny, but the helix is about all thats left of that layout.

    The problem with the helix was it could not take double stacks or multilevels as the was slightly too little clearance... someone never thought to accomodate them! Pigs on 89' flats no problem, but nothing taller. There was never any problems as far as derailments are concerned... you did however have to know you car fleet and know which cars were restricted to the rear of the train. Such restrictions are annoying, but the prototypes have the same considerations in mountainous trackage, so you could say it adds some realistic operating considerations.

    Make you helix the easiest trackage to access on the whole layout... trust me! After clearing your first major wreck, you'll thank me. Ours was a P.I.T.A. to access 50% of the track. Judging by your design, you've got that part covered.

    The layout I'm now planning (a few years down the road) includes a helix that is also located on an island. But it'll be 5' in diameter (two to three tracks) so I'll have plenty of room in it. I'm trying to have ample overhead clearance, nice gentle curves, and a gentle grade. Here in Ontario, CN & CP don't like putting too much power on their trains (singles are very common on CP), so I don't want to overwork the locomotives. I'll post picks in about 5 or 6 years! :)

  15. marc gast

    marc gast Member

    Helix Hoss


    Thanks for the update on the helix. Yes, with the disign of the helix going under the area which is already part of the layout, it makes sense. Good planning!

  16. Hoss

    Hoss Member

    SS, I'll have to look into those pre-made jobs. I was unaware that anyone made such a thing. If you happen to run across a web link somewhere on them please post it. In the meantime I'll start searching to see what I can find.

    Fifer, the plexiglass is a good idea, although I'm not sure how easily it would cut.

    Lock, 30-40 car trains are probably about the longest I'll ever be running, so HOPEFULLY I won't have any (or many) problems. I had thought about putting some kind of runaway track between the helix and the yard though.....allowing a runaway train to either divert onto the runaway track or completely derail before crashing back into the full staging yard. Don't know if that would work or not, but it's something I thought about.

    Marc, no problem. Thanks for your comments.....to everyone.
  17. lock4244

    lock4244 Member

    I never had any runaway problems on my helix. If a train came apart, they cars would free-wheel for a bit, but would stop long before they became a problem. These were micro-trains equipped cars. If you have Accumate trucks on your cars then your going to have some damage! Those things roll too well. And as many on this list know, if your using Accumate couplers then you WILL have unwanted uncoupling on the helix and disasterous runaways. The MT's were so reliable that a runaway track never even crossed my mind.

  18. Hoss

    Hoss Member

    Well, so far I have both Atlas and MT cars, so I have both Accumate and MT trucks (and couplers). I may get around to changing them out....or I may not....who knows. I'm nowhere near that stage in the game yet.

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