Has anyone ever built a helix directly on foam? My lower level consists of 1/2" ply with 2" foam on top with 2x4 frames. My helix will be 28" radius using 1/4" 5-ply, about 5 turns. Each arc is less than 1/3 of a complete turn so the weight would be more spread out due to overlap? Part of the second level would be supported by the helix as well. It's at the end of a peninsula and will go around the outside. My concern is the 2" foam not being able to support all this and possibly causing 'sinkholes' at the supports. My supports will be wood blocks.
Option 1 Leave it, it will be fine.
Option 2 Cut out holes in the foam for supports to go directly onto the 1/2" ply.
Option 3 Put an initial circle of support with the 1/4" ply, on top of the foam, then build directly onto that.
What are your thoughts/experiences?
hi
I've never built a helix, just thinking of the support issue, I'd probably do #2.
Although you don't mention exactly what the wood blocks are.
Mike.
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I'd have the blocks bearing directly on the bench structure below, and not on the foam.
I think the way to go with a helix is several threaded rods with double nuts and large washers on the underside of each level. Something chases just back off the lock nut and readjust. Then lock it back down again.
There are two things to consider in my opinion:
1: Grade is calculated railhead to railhead depth and diameter of circle.
2: Clearance is depth from railhead to bottom of next circle up. If two inch foam is on top of your plywood that will eat up space that would other wise be clearance. Keeping the same clearance will greatly increase grade unless the diameter is greatly increased.
Even a little sag or hump in a helix can cause a problem, so I personally wouldn’t build on the foam in any way. I’d probably try to support it from the benchwork frame below, but I’m a belt-and-suspenders kind of guy.
¼" plywood is pretty thin for the deck. How will you handle joints between segments of the deck? ¼" laminated into ½" decks with overlapped seams has worked well in HO, but would require more clearance per turn.
Helixes don’t abrogate the laws of physics, unfortunately.
Good luck with your layout.
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I think that's what I'll end up doing. Just seeing if anyone else had experience good or bad of having a helix supported by foam.
The foam is strictly the ground. For the helix, the track will be laid with no roadbed, directly on the 1x4 wood.
I actually made up a crude test helix using 1/8" board. It worked as long as the supports are plentiful. For the real deal I plan on using spacers made from 1x4 cut to 3". While this is a tight fit, it was doable in the mockup I made.
Using 1/4" plywood is flimsy, however, you will need to connect the joints somehow, and this is best done by making twice as many 1/3 circles, and overlapping the pieces and staggering the joints. This will yeild a strong roadbed for your track, However, it will be 1/2" thick. You will find a helix to be quite heavy, particularly if it has to support the upper layout! Mine is a 34" radius with double track and serves 3 levels, so it is bound to be heavier then the one you describe, however, it weights over 200 pounds!
You definately need to suport it with joists underneath it, and not foam. Even if it ends up weighing only 55 or 60 pounds, it will soon warp your structure without proper support. Use the afore mentioned chart to design your helix and don't forget to allow enough space between the top of rails to bottom of next circle of wood, to accomodate your rolling stock.
A helix can be a fun project or it can turn into a nightmare.