Articles - Helix
01/05/2003
This article describes how I built a ten-level helix from the visible portion of my N-scale layout down to a storage yard below the layout. This diagram shows the track plan for the top of the helix and for the bottom level. The entire helix was double-tracked. The radius of the outside track is 19 inches (48cm), with an effective gradient of 1.75%. The inside track has a radius of 17 inches (43cm) with an effective gradient of 2.3%. Each level has 23 feet (7m) of track on it. Total track length is 254 feet (77.4m).
Helix
The first diagram shows the top view of one level of the helix. It gives the overall dimensions of the sub-roadbed (luan board) material. We will be cutting two halves and two straight sections.
Helix
This is the side profile of the base frame of the helix. There will be two pieces of 1/2" plywood attached to each other via 1" x 2" stock wood strips. These strips will be spread throughout the structure to provide rigidity to the structure, and to provide ample surface for attaching the vertical posts that hold the sub-roadbed. The strips will be offset 1/4" away from the edges of the plywood so that the vertical posts will not have to have large areas of wood removed (these will "hang over" the edges of the sub-roadbed luan board).
Helix
In the diagram below we have super-imposed the vertical strips made out of high-quality 1" x 2" stock pine. These will have grooves cut into them to support themselves against the base frame and to support the sub-roadbed luan board. The sizes listed next to each strip indicates the relative offset that the sub-roadbed grooves need to be, measured from the top of the base frame. In other words, this is the implementation of the grade of the sub-roadbed. The "entry point" is where the distance says 0" and goes around clock-wise. We came up with these numbers by measuring the distance between the vertical strips and, with the desired grade, calculated the relative rise that needs to occur at each vertical strip location. Some small round-off was included to make measuring these distances manageable (see table below for the values calculated in Excel). The last entry, #8, was just for verifying my logic. The Distance From Entry Point is the inside radius of the curves.
locationDistance from PreviousDistance from Entry PointRise Req'dHeight Delta
00.0000.0000.0000.000
118.50018.5000.3730.373
212.50031.0000.6250.252
312.50043.5000.8770.252
418.50062.0001.2500.373
518.50080.5001.6230.373
612.50093.0001.8750.252
712.500105.5002.1270.252
818.500124.0002.5000.373

Helix
The last design diagram is that of the vertical pine boards that will provide the support of the sub-roadbed. The areas which are indicated by "varies" are where the sub-roadbed level changes are going to be implemented (i.e. implementation of the grade). The boards will all be attached to the base frame a half inch below the frame. The 1/4" grooves will vary vertically based on the spacing indicated in the table above. In the future we will have masonite board to wrap the outside of the helix and that will be attached to the outside vertical boards.
Helix
On April 19th, 2002 I started the construction of the helix. After spending time building the prototype to get a better feel for what I wanted, and, as seen above, spending some more time coming up with a more thought-through design, I'm now starting to build. I started with the base frame, upon which is what the whole helix will be built. The helix is designed to be removable and it is self-supporting. The photo below shows two pieces cut out of 1/2" birch plywood. I chose this wood because of its smooth surface and its high quality. It is also resistant to warping. The photo shows the pieces temporarily clamped together on a piece of particle board.
Helix
The unit has been rotated 90 degrees from the photo above. The three pieces of wood on both straight sections of the oval is what is holding the two plywood pieces together for now. All the various pieces of wood you see here serve two purposes. One is to provide support for the other set of plywood pieces. The other purpose is to provide plenty of mounting surface for the vertical stiles that will hold up the luan sub-roadbed boards later.
Helix
After the glue dried I drove in wood screws for added support and attached the other set of birch plywood boards. After sanding the boards, I'm ready for the next step.
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This photo shows all 16 vertical post boards lined up and ready for the router. The boards are 30-inch, 1" x 2" pine boards that are nice and straight.
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With lots of clamps everywhere, I started by cutting two 1/2-inch grooves. These will take the base frame plywood boards (built above). I took a piece of straight scrap wood and used it as the router's guide for cutting the straight grooves by hand. The pencil marks seen on the boards are where this guide board is placed so that the router is positioned correctly.
Helix
After the two grooves for the base frame were cut, it was time to line up the boards such that they are appropriately staggered. This allows me to cut 1/4" grooves straight across the boards. The grooves are for the luan board sub-roadbed. The boards are staggered to account for the grade changes.
Helix
All the major cutting is complete, so it is time to move the structure into the model railroad room. I decided to dry-fit all 16 vertical boards to the base frame and then install the luan sub-roadbed, AMI Roadbed, and track as I proceed. After it is all in there, I will screw the vertical boards to the base frame. This photo shows the vertical boards loosely installed and the first rung of luan board is in place. I don't have the legs yet so the base frame is supported by four plastic containers, because the vertical boards stick out below the base frame by 1/2 inch.
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Here is a low-angle view of the set-up.
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I decided that before I get too much track on the helix, that I install the legs first. The helix needs to be self-supporting, so I am going to install four legs under the base frame. The legs need to be removable so that I can move the helix out of the room. The photo shows the parts used to connect the legs to the base frame. The bolt that has two threads on it will be mounted in the 2 x 2 poplar legs. The square mounting plate will be permanently attached to the under side of the base frame using the four screws shown. The nut will be screwed on to the bolt of the leg (you will see later).
Helix
On the bottom of the legs I will install this foot. It has an adjustable range of about one inch. This will allow me to make sure the helix is level. I will not install this part until the whole helix is finished. The legs are 36 inches long, but when the track is all built, they will need to be cut to about 33 inches.
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This is a close-up shot of one of the legs installed.
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And this photo shows all the legs installed. I will need to build some cross bracing because right now the helix table is quite wobbly.
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The vertical boards have been installed (they are only snug-fitted to the base frame), and the whole helix has been moved into its position within the room.
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These are the luan boards cut and ready for all the levels.
Helix
This is what it takes to build a ten-level, double-tracked helix: 18 bundles of 18 feet of Micro Engineering code 55 unweathered track, nine rolls of AMI Roadbed, and a collection of rail joiner packages.
Helix
The time has come to start putting track on the helix. This is a big project, with the potential of getting bored with it along the way. I have therefore decided to work exactly one hour each day on the helix. This will allow me to make good progress while not getting burned out on it.

First off I needed to secure the legs of the helix "table" a bit so that it wouldn't rock all over the place. I did this by clamping some 1 x 2 stock to three sides of the table. The fourth side is left open to maintain access to the inside.
Helix
As I'm laying track, I also need to keep moving forward with laying the sub-roadbed plywood. You can't move too far ahead, or you'll block access to the section where you are laying track. Here a half-circle is being glued to a 12-inch straight section with a splice board under the visible plywood. Small clamps provide just enough holding power without being too heavy for the plywood itself.
Helix
When the track is shaped to fit the AMI Roadbed, I pull it off again and spread the glue on the AMI Roadbed. I place the track on it again and put some moderately heavy weights on the track to hold it while the glue dries. By the way, I started using rubber cement for the glue, but while I was about halfway up the helix, the track in these lower levels started to come loose! I switched to using Liquid Nails for the glue. I had to go back to these lower levels afterwards and carefully re-apply Liquid Nails glue. Not fun!
Helix
I decided to attach track feeder wires at the tops of each side of the ovals. Since this track will ultimately not be visible, I decided to simply solder the wire to the side of the rails. To keep from reducing the overhead clearance between helix levels I decided to cut away a bit of the AMI Roadbed and lay the wires under the track instead of routing it through the plywood. Later on I will have heavier gauge power wires run down each of the ends of the oval and connect all these feeder wires to the heavier bus wire.
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Finally, I am approaching the completion of the first rung of the helix. Just as a sanity check, I placed a box car on the lower track and made sure I could lift it out of there in case of trouble. No problems.
Helix
Here is a close-up of the track being glued with Liquid Nails. I used a caulk gun to place a bead down the center line of the AMI Roadbed material, and used a scraper to spread it out thinly before placing the track on it. As shown before, some temporary weights will hold the track firmly in place until the glue dries.
Helix
Even though I have about 4 rungs of track up, I wanted to make sure and do a sanity check. This photo shows two Rivarrossi passenger cars (the longest equipment I run) next to each other on the helix. A tape measure is holding them in position while I took the photo. As you can see, there is plenty of clearance between each other and the vertical boards.
Helix
I wanted to show some additional construction photos of the helix. This one shows how the various levels are held up by the vertical boards. You can also see the spline pieces of luan board used to connect the semi-circles and the 12-inch straight sections that make up the oval shape. By leaving the vertical boards loose while laying the track, they can be moved out of the way to lay and bend the track to fit the AMI Roadbed. The corresponding vertical board on the inside of the helix holds the various levels up while the outside one is briefly removed.
Helix
This is just a photo of the inside of the helix. The luan board sub-roadbed is always at least a half rung ahead of the track. This allows the wood glue to dry that is used to connect the wooden pieces, and for me to place the AMI Roadbed on the next session. There are really four steps to iterate through in a work session. First, I make sure I have installed as much wood sub-roadbed as possible without interfering with track work on the rung below. Next I make sure that as much AMI Roadbed material has been placed as I can. I also check to see if there are any more track feeders to solder into place at the ends of the oval track. And, finally, I lay as much track as I can. There is usually enough work to do to fill up an hour before working on something that hasn't quite dried yet.
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I have marked the inside levels because I got tired of counting. Level 1 means the zeroth rung (no helix track), so the number of rungs is one less than the level indicated on one of the risers.
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I completed the trackwork of the helix on July 26th, 2002 at 1:20pm! I started the trackwork on June 16th. I diligently worked one hour each day with a 4-day break to recover from a foot injury. That is a total of 36 days, or 36 hours of work. The project went smoothly. I highly recommend using Liquid Nails for Projects. I have had to go back and put some Liquid Nails under the track where I used Rubber Cement, because after about 5 weeks some of these areas had come loose. The photo below was taken when the trackwork was done. Rubber bands on the top of the risers keep them in place temporarily. The small clamps on the left hold a temporary straight section of plywood in place. This will be replaced later with plywood that will be custom-fitted to the rest of layout. The helix is not in its final position in this photo. I moved it around so that I could have access to all the areas around the helix.
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Here is a dramatic low-angle shot of the entire structure. The slotted riser method has worked well, and I would highly recommend it. Leaving the risers loose while laying the track allowed me to remove them one at a time to bend the flextrack around the curves. Eventually some of the risers got a little too loose and had to be held in place with rubber bands.
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The risers in the back have the words "tunnel portal" written on them. This is where the track will come out of a tunnel and be visible. This is important because even though Liquid Nails worked great, it is very messy. Not something that you want under visible track. This track will be kept in place with ballast.
Helix
The next big step was to run a train through the helix to test the track. I decided to run a Life-Like C-Liner and six Rivarrossi passenger cars from the top of the helix on the outside track down to the bottom. This locomotive has not been converted to DCC yet, so I used our old starter-set transformer to run the locomotive downhill. This photo captures it in action.
Helix
After the locomotive made it down with absolutely no problems whatsoever, I decided to run the worst-case scenario. I had to test the helix to find out where its limits lie. I put this same train on the inside track on the bottom rung. I made the train go uphill, backwards pushing the six, un-weighted passenger cars. The passenger cars are the longest rolling stock I have. The track had not been cleaned and the full 125 feet of track was being fed only from the bottom-rung connection. This was truly the worst-case scenario! The train made it uphill with no problem at all. The curves are really too tight for the passenger cars, but there was about a hair's width between the cars as they made their way up. It was very satisfying to see the train make it up without a hitch.

After the short victory celebration, it was time to continue the work. My next task is to secure the vertical risers to the rest of the helix structure. I attached them on the bottom with a 2-1/4" screw to the wooden blocks in the helix base. On the top I used clamps to hold the risers in place while I attached the screws. Of course, I made sure the risers were indeed perpendicular to the helix base and that the matching pair of risers lined up with each other across the track. The next step will be to use a pneumatic nailer to drive in some brads between the risers and the luan board sub-roadbed.
Helix
The leg supports you have seen in photos up to now were just temporary. It gave me some time to think about the final design of the leg structure. Since the helix is meant to be removable from this layout, it was built separately from the layout. Because of this, the helix needs some vertical flexibility to make sure it matches the height of the layout. I installed 5/16" tee nuts and matching bolts on the bottom of the legs. The legs, by the way, are made out of 1.5" square poplar. The next photo shows the leg structure in place. I used two 4-foot boards that are bolted to the legs. The scrap pieces left over from trimming 3.5" (~9 cm) off of the legs were used as separators between the cross braces. When installed, this method makes for a very sturdy structure. Three of the four sides of the helix legs are done this way. The fourth is left open to gain access to the inside of the helix. I will trim the boards later. The bolts are 1/4" by 2.5" and 1/4" by 3".
Helix
The fourth side, without the benefit of the cross bracing, will be the weak point of the leg structure. The A-frame shown in the photo below will be used to attach the helix to the rest of the layout's framework and to provide lateral support for the helix itself. There are two of these A-frames.
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This is a CAD drawing of the A-frame, with a second drawing showing the key dimensions.
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I installed the bracket arms/A-frames that I built. The photo below shows a close-up of the bolts connected through the helix base frame and the horizontal member of the A-frame. This is a view from inside the helix.
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Here you can see the two A-frames installed. They don't interfere with the operation of and access to the helix, nor do they interfere with the track that goes around them to the storage yard in the back.
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Even though the design and construction of the A-frames went well, the installation is a problem here. I intended to attach the upper part of the A-frames to the L-girder right where the C-clamps are, but realized that the drill needed to create the bolt holes wasn't going to fit in between the L-girder boards. I need to gain access to a 90-degree, close-quarters drill to drill the holes and install the bolts. I will do that later. For now the clamps are holding things tight.
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I rented the right-angle drill from NationsRent and put the four bolts in as highlighted with the red circles. The drill made easy work of it.
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Now I need to turn my attention to connecting the helix track to the double-track mainline. First I cut a custom-fitted piece of luan board that went between the helix plywood and the existing mainline sub-roadbed. In the photo, a temporary piece of plywood is used to hold up the sub-roadbed plywood that is being glued.
Helix
While the glue was drying, I started the wiring process. I tapped into the mainline feeder bus that runs under the double mainline area and routed a set of wires to the rear of the helix. Here is the snake of connectors. I was dreading this part of the job, but surprisingly things went fairly quick and smooth. The feeder wires are held in place through plastic ties. For fun, I ran a train before installing this feeder bus and after. There is a significant difference in performance. Even though the rails are soldered together in the helix, the resistance of the rail metal is quite obvious over a 125+ foot run!
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I finished applying ballast to the top level of the helix (which will be visible).
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At the other end of the helix, I am attaching another piece of 1/4" luan board to connect the helix to the storage yard below the layout.
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I installed train detection circuitry and its wiring (see Helix Elevator Lights article about that). This is the last view of the interior of the helix, because the next step is to cover it with Masonite board.
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I attached the Masonite board to the vertical posts of the helix. At the front of the helix (right-hand side of the photo), you can make out the LEDs installed into the cover to indicate the train's relative position within the helix. This was not a trivial process.
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Here is the view from the top with the cover installed.
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I applied putty to the screw holes, sanded, and re-filled, and then eventually painted the whole helix cover (and the layout's fascia panels) a dark green color (hard to see in the over-exposed, flash photo).
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I later on built this huge mountain on top of the helix. The track at the base of the helix was a reversing loop I built on top of the helix before building the mountain.
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Why did I make the mountain so tall? Well, this is the inside-the-helix view (I'm laying down on the floor). I can actually stand up in the helix (I'm 6'4") and be able to deal with any derailments or other issues in the helix. I really enjoyed building this helix. If I need another one, this is definitely the method I'll use. I have pretty much sworn off double-deck layouts, though, because of my back. However, I hope this article provided you with some info if you are thinking about building your own.
Helix