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My second layout had a helix that I put together without much insight into how best to do it. The helix was about 24 inches in diameter and was constructed using the same plywood as my benchwork, with the usual cork roadbed. It was only accessible for cleaning from one edge of the layout so there had to be enough room between levels to get my arm through. The result was so steep that it was pretty much one way and, despite my intentions, cleaning the track required a contortionist. This was the weakest piece of my layout.
On my current layout I focused on a low grade (I chose 2%) and easy access (from the center, thank you). I ended up with a reliable and compact helix with a decent grade and with very reachable track. Having toured many layouts in the intervening years I haven't seen any with helices built using the same approach. The reliable ones are large and many are prominently located at the edge of the layout for track access, taking up a big chunk of the most valuable real estate on the layout. So thought I'd try to describe it here for the benefit of anyone who is considering building one.
[IMG]https://www.nscale.net/forums/attach...4&d=1581530278[/IMG]
First off, having access from the center allows you to locate the helix in some corner of the room instead of out in the open. There is no need to provide enough clearance for your hand or arm, so the rise per revolution can be based on NRMA clearance heights instead of your anatomy. Track cleaning is as easy as spinning around in the opening, and you get an access hatch to reach any nearby track. I think most people avoid this due to fear of string lining a train to the floor. This is a real concern, but insurance is simple and cheap, in the form of a foam board on a clip for me.
[IMG]https://www.nscale.net/forums/attach...3&d=1581530278[/IMG]
I've had a train fall once due to a flex track issue described below, and it fell to the board without damage.
On any helix there is a tradeoff between footprint size and grade. To keep the grade down most people make large helices; this one has a 30 by 35 inch footprint including the framing and a 2% grade. The key to lowering the grade and reducing the footprint is to lower the rise per revolution. Things that bloat the rise per revolution are thick subroadbed and thick roadbed, including cork and Unitrack-style rail. Best to go with the thinnest possible sub roadbed, no cork, and code 55 flex track. The sub roadbed that I used is a countertop laminate (like Formica) which is very stiff, strong, not too hard to work with, and (most importantly) maybe a sixteenth of an inch in thickness. You can get an N scale NMRA height clearance (1 9/32 inches) above your rail with a little over an inch and a half rise per rev.
Because the helix exit determined the relative heights of my layout level, I built it before adding upper level benchwork. I included a continuation below layout grade in case I want to add staging below the layout later.
The frame is a 1x4 box with carefully cut gussets above and below each corner. Each corner gusset has three facets, the center being at 45 degrees and the other two being at 22.5 and 67.5 degrees. These facets are key to attaching uprights, to which the laminate sub roadbed gets attached.
[IMG]https://www.nscale.net/forums/attach...8&d=1581532830[/IMG]
I am fortunate enough to have a decently equipped wood shop with a bandsaw and a radial arm saw instead of a table saw. (Radial arms have been superceded by power miter saws). The bandsaw was used to cut those facets, and a table saw or power miter saw is capable of making repeatably spaced cuts in plywood. Frame construction is shown here, apologies for the quality of the drawing:
[IMG]https://www.nscale.net/forums/attach...9&d=1581532830[/IMG]
Note I chose an oval shape - not critical but those straight sections are handy for turnout placement.
There are many ways to make uprights. I cut evenly-spaced kerfs on plywood at a slight angle on my radial arm, then ripped crosswise into 18 individual uprights. The kerfs are way wider than the laminate thickness. It might be easier to use unkerfed 1x4s for uprights and glue wood blocks to them to provide a gluing surface for the laminate, although this would make the frame dimensions bigger. Carefully construct the lowest level then stack and glue blocks as you go to construct the next level up. You could use 1x2 trim cut into blocks, which would give you 1 5/8 inch clearance above as you stack them on the lower revolution of laminate. At any rate, take extreme care locating and attaching the uprights to the frame; squarely vertical and that those kerfs have to increment upward just right to make a full rise in one rev.
I cut the laminate using a band saw (a hand held jig saw would work) in sort of J shapes for nesting; they can be seen here in this from-the-floor shot. Choose a finer-tooth blade to avoid chipping. Laminate comes in large sheets that they will roll up to fit in your car.
[IMG]https://www.nscale.net/forums/attach...6&d=1581530278[/IMG]
Round off the sharp edges on the inside with a file so you don't cut yourself later, then glue them with an expanding urethane glue like Gorilla Glue.
[IMG]https://www.nscale.net/forums/attach...5&d=1581530278[/IMG]
Install that first level with care; the rise has to be right. Once you get the first level in, install the track and wire it before adding the next level. Stack spacers on the rail top to hold up the next level and glue that in. Note with glue drying times you get one level done per day: glue and solder the track, wire it, then add spacers and glue in the next level's laminate. Also note how wire is routed to the inside rail by going thru a gap in the ties on the outside rail. Make sure you can do this with your flex; otherwise you will need to route under the laminate, which requires more rise per rev for clearance...
I have a couple of turnouts in the helix, not the best place for maintaining them so make sure you have these working solidly before you hide everything under landscaping. They will probably require remote turnout motors.
Here is a shot of the now-hidden helix, looking down from a stool.
[IMG]https://www.nscale.net/forums/attach...0&d=1581538586[/IMG]
I added a forest cap so no plywood or foam would be visible from eye level.
[IMG]https://www.nscale.net/forums/attach...1&d=1581538586[/IMG]
One lesson learned was from the only derailment that I had in the helix. I used Atlas code 80 flex - not ideal as it has more height than code 55, but there is a gotcha with this type of rail. On Atlas (vs ME) one of the rails is loose. As was explained to me by very helpful folk here on NS.net, when you install this rail you want to install it so that that loose rail is on the outside of the curve. The thread: https://www.nscale.net/forums/showth...ex+gauge+helix
And when planning your helix, consider the effect that curves have on pulling trains up hill. There is a calculator here but I can't vouch its accuracy. For example the formula doesn't seem to account for how long the curve is - a quarter turn shouldn't be as tough as a 360 helix. http://railroadboy.com/grade/
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