I’ll be moving (yeah!) to a house within the next month and getting a 14x24 garage that I’ll share with some shelving and the inevitable lawn mower (I’m trying to negotiate a garden shed).
Anyway, this means that my 2x8 layout will soon have a great deal more room to live in. It’s obvious that I’m going to expand off both ends of it, but I’ve got a problem of some interchanges that really need to go somewhere.
So I decided that my layout needs a basement. It will be pure track - no scenery - just a bunch of staging yards essentially.
The scale is HO.
I now have a number of questions:
What is a recommended height difference between levels? The normal width of the layout is 2 feet wide - it will be up to 4 feet wide at the ends, where on one end there will be an oval helix (more later) and on the other a horseshoe curve. I think that as long as the basement is at a comfortable level off the floor, 1 1/2 to 2 feet should work.
Slope… what is the run/rise for a 2.5% slope? I figure I can get away with that on both the UP interchange track, which will decend from the back of the layout near the middle to one end of the layout, and on the oval helix.
The oval helix - my idea is that I’d like to see if 24" radius curves would work if instead of a pure circle the sloped sections are straight and the curves are level. I think I can fit a 4x6 section (possibly longer) in for this. I can’t quite see dedicating a 5ft square to this in order to get a wider radius curve. I may have to of course… am I nuts, has anyone ever tried an oval helix?
The difference in height on my layout will be something like 18 inches (it varies, as track on both the upper and lower levels is not flat). There are a variety of sources that talk about level separation. Jim Hediger’s Ohio Southern stories in Model Railroader covered his level separation in some detail. I don’t remember the specific article. I think one of the Armstrong track planning books also covered it a little bit. Joe Fugate also talks about level separation in his DVD series on his layout (I don’t remember if it was in volume one or two, but he’ll probably chime in here anyway).
Slope is easy - 2.5% is 2 1/2 inches rise over a run of 100 inches. Just multiply the percent grade by 100 to get the rise in inches over 100 inches of run.For a 24 inch radius helix, you have 150.8 inches of run, roughly, which gives you 3.77 inches of vertical separation between rails from one loop to the next - pretty minimal. You’d have to use very thin material to be able to get trains over the helix!
I don’t think the use of 24" straight sections will allow you to make the semicircles flat - you would be climbing at least four inches in only 48 inches of run - a grade of 8.3 percent! It’s even worse because of the vertical curves at each end of the straights, to come out level with the flat curves. Your actual max grade would more likely be in the 15-16 per cent range! Personally, I’d go with the “oval” with the grade running throught both the curves and straight sections. That gives you 198.8 inches of run per loop, and a separation of 4.97 inches between loops at a 2.5% grade- much more workable. In fact, that’s exactly what I’ve done on my helix plan - I have 24 inch straight sections between semicircles, to ease my grade. (BTW, “oval” isn’t really an accurate term, though it does get the point across. A true oval has no straight lines, just curves of varying radii).
So I’d be looking at 3 1/2 loops on the helix as well. I’m beginning to wonder about the “around the back” path that the other train will be taking as well. If my math is right, I’m looking at over 60 feet of track to decend from one level to another… that isn’t going to happen.
Not a huge difference. Either way, your helix — be it circular, or eliptical — will eat up a large amount of real estate.
By the way, a 24" radius curve is wider than 48" diameter since measurements are to the center of the track. You’ll have to factor in at least a couple additional inches of clearance on each side. That makes a 24" radius helix closer to 52" (or more) in diameter.
I think at this rate I’m going to try and keep it single level… the nice thing about doing the planning mentally is that tossing out the current plan and coming up with another doesn’t waste any paper!
As an aproximate rule of thumb I figure 1" of rise for 8’ of length equals 1 per cent grade (I know I’m 4" short but this isn’t rocket science and my rule of thumb can be worked out in my head). With 60’ of helix my (admitedly rough) calculation make it a 3 1/2 per cent grade to give you 18" of seperation. Steep but doable if you’re not planning on running long trains.
Mouse, everyone already knows pi r round. LOL OK, I’m not getting the math here. Maybe I’m not quite with it today, but where do you get the “plus 48” from. I’ve looked at this for about 15 min. and still haven’t figured it out…(just blind maybe) Wouldn’t one loop just be 3.14 x 48 aka pi r?
Yep, blind! Forgot he is going to do an oval with 2’ straight… Shouldn’t multitask at this time of day. heehee
If you can swing it space-wise, a single deck layout is certainly simpler.
My Siskiyou Line has a deck separation of 12-13". Of course with the mushroom, you are not especially concerned with seeing the upper deck and the lower deck together, so you can take advantage of the raised floor to adjust the viewing height of the upper deck.
But the basic rule is make the lower deck as high as possible and the lower deck as low as possible so you can get between the decks with minimum hidden trackage.
A helix is an abysmal layout construct. It takes a massive amount of space and you can’t scenic that space in any way that’s at all realistic, so it’s layout real estate that you simply have to throw into a black hole and use to get between levels. The fewer tiers it takes to get between levels the better.
My helix for the Coos Bay branch connection to the Siskiyou Line main is pretty modest … a mere two tiers. Yet the helix contains fully 1/3rd of the branch line trackage - yuk! Imagine what we would be looking at if the helix needed 3 or 4 tiers to get between levels!
If you need multiple levels to get everything to fit then the mushroom is a great way to go because the layout doesn’t look double decked, but if you have the space, single deck is the best of all.
I think I’ve given up on the idea of double deck trackage - you’re right, it simply eats too much space and track for the benefit, especially in a smaller area.
Expect an e-mail soon… I’ve got a couple ideas I’d like to bounce off you.