Helix Construction Ideas
To Separate Model Railroad Decks

Many model railroaders turn to helixes to gain altitude and provide separation between decks in order to gain a longer mainline.

While on the 2012 Muskoka Tour I visited the HO layout being built by Roger Moses in Innisfil south of Barrie, Ontario.

He is at the tracklaying stage now that his basic benchwork is completed. I was very impressed with the neatness of his construction and the way he has incorporated a helix into the layout.

His idea is similar to mine but he has done a far superior job. He has used threaded rods to keep the spacing exact as the roadbed climbs. This provides a constant, adjustable grade. He used expensive plywood for stability to avoid shrinkage and warpage.

threaded rod helixThreaded rod helix
cloeup of helix threaded rodsCloseup of helix construction

A helix takes up a lot of space. Depending on the scale this can eat up a lot of your modeling space. In HO scale, to keep the grades reasonable and to minimize derailments, it's advisable to use a radius of 36 inches or greater. That's a big chunk of real estate.

Fellow modeller John Houghton worked out the math for our new club layout where a helix will be required. 

Minimum height rise needed for a helix that goes once around on itself to clear HO NMRA gage is 3-1/4”.

Assuming a maximum 2% grade, this means a circular helix requires 13’-6” circumference or 26” Radius. A 2% grade rises .24” in 1 foot.Leaves no room for fingers to get over a car in case of derailment.

To allow for additional height for fingers, the following indicates what we need. This is assuming a Circular Helix.

  • 4” rise (3/4” finger clearance) : 16’-7” circumference : 32” Radius
  • 5” rise (1-3/4 finger clearance) : 21’-0” circumference : 40” Radius
  • 6” rise (2-3/4” finger clearance) : 25’-0” circumference : 48” Radius

I took a different approach to helix construction. I had salvaged a helix I had built on an earlier layout and had moved it in pieces to my previous home. I decided to build a scenicked, non-traditional helix by adding splices into the original subroadbed helix construction.  This allowed the track to climb the mountain without always being directly over itself. Where the track is directly below a lower loop it can't be seen. 

offset helix constructionMy offset helix construction

Helix rings offset so that a lower track is outside the next loop. Note the lower loop tunnel portal in the upper right of the photo.

scenicked helixSeparation of two loops on the visible side of the mountain facing the aisles.

The grade was not constant on this reincarnation of my Utopia Northern nor was the radius. Operators had to be on their toes to maintain a constant speed.

It also meant helpers were sometimes required, especially on steam trains. It made for some interesting mountain scenery with the track going through cuts or hanging on the cliff edges.

I found this more satisfying than just having the trains disappear into a hidden helix tunnel. My railroad used single track on the offset helix with trackside signals to control train movements between Underhill South Jct. and Buffalo Peak station at the top of the Big Hill. A helper could be parked at the bottom or top of the grade.

styrofoam helix sceneryInside the helix construction. Scenery is stacked blue styrofoam

I could still get inside the helix for maintenance or in the case of derailments. Yes, it happens!  And one still has to crawl under the layout to get in there.

Grade separation

I had to use 13 inch separation because I had a G scale deck above my previous HO layout. The HO layout only had upper decks in the center peninsula, not around the walls.

The G scale layout went around the walls with a 20 inch separation from the HO layout.  I found 16 inches comfortable to work with. This still left room for a valence to hide wires, switch machines and lights under the upper deck. A foot is a little too tight.

To John's point above, even in N scale because you often need to reach in with your hands and they are not N scale size.

It certainly limited use of the staging tracks under North Point. However, model railroading is a series of compromises so you work with what you've got! I've seen HO layouts with 5 inch separation between staging and the next deck. This can be a hassle for finding or rerailing cars and for mounting switch machines.

fascia platesFascia plates

Roger had an interesting way of mounting fascia plates to the plywood benchwork. The screws are similar to ones that can be used when installing acrylic guards on the edges of benchwork to avoid cracking the plastic.

threaded rod decking supportThreaded rod support

I also used the threaded rod technique to hold up part of the G scale sub roadbed. This was in the city of Utopia. I had planned to disguise the rod inside a building or chimney but never got to it before dismantling this layout in 2014 due to a move to a new home.

There have also been some articles with helix construction ideas in Model Railroad Hobbyist, the free Internet magazine. Check their archives.

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