Page 16 - May June 2012

Circles on the mind – or building a helix Keith Webb
I was never a fan of multi-deck layouts; this is quite possibly because they are not comfortable to use when you are vertically challenged! However, following a failed attempt at moving house, resulting in the complete removal of a partially built layout, I found that I had to consider redesigning and rebuilding my layout with the view to it being moveable. Added to this I wanted to run reasonably long trains and include some switch- ing, but I also wanted it to be more than just a tail-chaser and if possible have a little purpose in its operation. So modular (not to be confused with NMRA modular), multi-level and inno- vative it would have to be.
I currently have a room that is approximately 10' × 24' at my disposal, of which the original build occupied close to 10' × 17' of this area. The original layout was pretty much a series of ovals with all the hidden storage buried behind removable sce- nery. This meant that there was virtually no switching and no operation. The new design occupies a reversed ‘J’ shape, with a multi-level helix at the end of the hook of the ‘J’ behind the entry door, and will have two separate helixes above each other at the top of the ‘J’.
Base of main helix showing section which includes lead-in and first turn)
Unfinished lower helix at ‘top of J’
This leaves approximately 18" of space left to the remaining end wall. This space was left for various reasons, but mainly to leave room to get to at least one window. However it does provide an opportunity for future add-ons and a line to the workbench.
The two helixes at this end will just take the track up (or down) one level, but even so, with 4" separation (for double-stacks). This still involves two and a half turns of the lower helix to allow reasonable access to the storage yard. The original plan was for 8" separation difference between these two levels, but with 3" supporting timbers being used it didn’t leave much room to get an arm in. We are all aware that there is a natural law that says: if you can’t get to it, then that’s where it’s going to fall off!
The upper helix may end up only going around 11⁄2 turns as the level of separation between the ‘high-line’ and ‘low-line’ is not quite as important – it’s all scenic, and there will be the option to have most of the ‘high line’ with a grade on it throughout its length.
Having cast around for a helix construction method to suit my situation, I found nothing conclusive to follow. So I decided instead to assimilate all the styles and information I had seen and gathered, and began to design and build my own style of helix. First I had to decide what the important criteria of the helix were. These turned out as: a gentle grade, modular con- struction, double track at a minimum 30" radius (to allow for tight passenger car connections and 2-10-4 Selkirks).
A gentle grade was going to work out as about 2.12 degrees (according to the 3rd PlanIt software tool). More of an incline than I’d hoped, but this can only be changed by lengthening the helix turn (larger radius or made oval). The only alternative is to lower the distance between levels. This would only be possible if I was only going to run 1950s era. However the cur- rent grade does not appear to look too steep to the eye, and fitted in with what other helix builders had achieved. If I do find that trains are struggling, I am quite prepared to use pushers, and this will add a little more operation and fun to the whole layout.
Double track, because on the main helix, the inside track would need to extend from Level 1 (storage) all the way to Level 4. The outside track would join Levels 3 and 2. The two other helixes would then link Levels 1 to 2 and 3 to 4 respectively. These two were originally planned to be single track, but I quickly realised that on the combined scenic levels of 3 and 4 there was the strong possibility of two trains passing, and I would also need somewhere to facilitate the removal of push- ers. Seeing as there is also a chasm planned with two single- track bridges across at the bottom of the J, a full-length passing siding was not going to happen unless I utilised the helix. The lower-level helix was doubled up to provide the same passing ability through the town.
Modular construction. As stated before, the whole layout is built with this in mind, as when I move, I do not want to have to start from scratch. There are mainly two reasons for this; cost of rebuilding, and time. Having a modular system allows for minimal remodelling if required. However, my initial plan of a couple of turns of the helix being itself a modular section that could be ‘rolled out’, went out of the window when I tried to ‘roll in’ the base for the first one. I had measured all the doorways it had to go through, but not the distance between the stairs and the end of the downstairs ceiling. Who would suspect this as being smaller than a doorway? So now each half- turn is a section, and once split, the two halves of each of the ‘smaller’ helixes will be removable as a complete half a helix.
Construction of the first and trial helix – the helix base
I first marked and cut a sheet of 3⁄4" ply into eight curved sections at least 1" wider than the helix sections. This is de- signed to form a sturdy base to the helix and will lie directly on the framework. I used a homemade trammel and my old tech- nical drawing set-squares to mark out the sections on the 4' × 8' sheet, then cut them out with a hand saw and a jigsaw. I found the jigsaw was not a good tool to cut straight lines, so used the hand saw for these. The sheet was marked so that the sections were laid out lengthways in an S-shape. A little wasteful, but I needed these sections to be complete (if marked out across the sheet, a good 11⁄2"–2" triangle was lost from each outside corner).
I then dowelled and glued these sections together in pairs, just relying on the dowels and mending plates for the other joints. Fixing a temporarily length of ply across the centre using more mending plates, I marked the centre and used the trammel again to draw two predetermined circles on the completed base. After making a large divider (using a piece of 5/8" square hardwood and the blue parts in photo 3), I marked out the hole centres for the studding that was going to hold the whole thing
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