Foam Helix Construction
Hi John,
Sure. I've built 3 foam helices and each of them has turned out great. Trains run through them flawlessly. Here's my process. Get a cup of coffee, as I'll try to be as detailed as possible.
Measurements First
Before planning and building the helix, I need to know some numbers. I figured these out when planning my railroad and doing the initial track planning. They are based on my room size, equipment, and operational goals.
- My minimum radius on the main line is 24".
- Maximum train length is 11 40' cars plus a caboose. This is governed by my longest passing siding.
- The maximum grade for my locomotives, figured out by using a test board, is around 3.5% pulling my 11 car train
- The minimum vertical clearance is defined by an NMRA track gauge. Adding the track height, I think it's around 3.5 inches.
Helix Planning
Armed with the above information, I figured out that I can build a 24" radius helix with 4" separation between turns and it comes out to about a 2.65% grade. Even allowing for a little extra drag caused by the curve, I know this works because I've built three of them! If I run longer through trains, I'll need double headed locomotives (but won't that be REALLY AWESOME!) :o)
I enclose all my helixes with fascia and scenery, so they're pretty protected once they're built. Because of this, I figured it was okay to use smaller foam, and that has proved very true. So the foam for the subroadbed is 5/8" inch foam. This means that the separation between subroadbed is 3-3/8", which meets my minimum vertical separation.
Helix Construction - First Level
To actually build the helix, I start by tracing arcs on 4'x8' sheets of 5/8" foam using a yardstick with holes drilled in it. I trace one line at 24" radius, one at 22" and one at 26". This gives me 2" of clearance on each side of the track center line. I also trace the perpendicular line using the ruler. This perpendicular cut line lets you join the sections together easily. I cut out these arcs using a break-off wallpaper knife.
Next I cut strips about 2" wide from a 4'x8' sheet of 1" foam. You could use the 5/8" foam too, but I like the wider foam for stability. I then cut these strips into pieces 3-3/8" long. These are my risers between levels.
All of the construction is done with hot glue.
The first loop of the helix is the most difficult, because you are going from 0 to 4". I start by joining sections of subroadbed with pieces of foam, using hot glue, until I have a 360 degree circle. Butt the ends together and match up the center lines. I use a cardboard template, cut to 24", to make sure I'm getting a smooth curve across the joint and I'm not introducing any kinks.
I glue the beginning of the loop flush with the level of the sub roadbed at the base of the helix and support the joint with foam pieces. Next I glue two risers at the end of one full revolution. I then glue the first loop to the top of these risers. The height of the risers on the rest of this loop depends on what's underneath. If the support underneath is the same level as the beginning of the helix, you can do some math and divide the riser height in half, quarter and three quarter. Then cut and glue risers in place. If it's open benchwork, it's a little harder. I've used a laser level to good effect. I set it at a point 2" above the base of the helix, then supported the helix at that height with risers placed 180 degrees around the first turn. Then I do the same at 1" 90 degrees through and 3" 270 degrees through. Finally I place other supporting risers to stiffen the whole construction.
A note about the risers: They don't have to be perfect. The hot glue takes some space, so I usually cut them a little short and allow the bulk of the glue to make up the difference. Also, you can glue them to the outside of the helix turns, or the inside, and measure the distance between the levels with a ruler or spacer. Then the foam cutting doesn't have to be so exact. Also, make them far enough apart that you can reach in to clean the track.
As I build each level, especially the first, I also use a small level to make sure the sub roadbed is level side to side and not tilting out. A little tilt in is okay and acts as superelevation, but don't get too much. I also use my iPhone to check the grade % and make sure I'm close to what I planned.
When the first level is in, lay the track. Run a train up it to check for vertical kinks, etc. Make sure things run smoothly before proceeding.
Helix Construction - Remaining Levels
The remaining levels are much easier. There will be a constant separation of 3-5/8 (or whatever you figured out) between each level. So the risers are all exactly the same height. Keep adding arcs of roadbed supported by risers, and lay track as you go, running trains up it to check for smooth operation. I like to run an empty train up backward to make sure nothing derails.
When you get to the top, you simply attach it to the subroadbed of your next level and you're done!
Miscellaneous observations
If you make a mistake or need an adjustment, it's EASY! I messed up one of mine and was making my risers 3-1/2 inch instead of 3-3/8" That meant I'd be a full half inch too high at the top! I already had three turns built with track wired and working! What to do? I went through and cut every riser in half. Then I cut a slice out of each one. Then I supported each level at the correct 3-3/8" and glued another piece of foam to the outside of each riser. It took about half an hour, and I had reduced the height of the entire helix. Problem solved!
I place the risers far enough apart that I can reach in to clean. I also stagger some of them between levels. This has an egg-carton effect and the finished structure is surprisingly strong and stable.
Because the foam is inert, it doesn't expand or contract much with changes in temperature and humidity.
Because the structure is stable, I solder all the rail joints. I haven't had any problems with expansion of the rail, but my basement is pretty environmentally stable. If you have big swings in temperature or humidity, you will probably want rail expansion joints. Stagger them so they are not side-by-side in the rail and there's less chance of derailement.
I use four 2"x2" legs with L-Girders to support the bottom level of the helix. The 2"x2" legs go all the way to the top of the helix. These legs are attached to the floor or the wall. I also attach each turn of the helix to these legs for added stiffness.
On one helix, I lined the inside of one of the turns and modeled it like a rock cut. I left a window in the fascia. This allowed operators to see the train halfway through, and it looked pretty cool.
I maintain access to the inside of the helix for track cleaning or derailments.
That's about all I can think of at the moment. If I've missed anything, or you want to see photos of any of these stages in particular, let me know and I'll see what I can dig up.
Thanks for reading!!
