25/10/2021.

Like many, I live in a flat, even if this flat is a bit atypical: first and only floor (so no galloping on the head…), a 40 m2 terrace, well much less if you take away the veranda and the multiple potted plants.

And like many, I was frustrated not to be able to run my train models. You will tell me that a few square meters are enough for that. Yes, as long as you are satisfied with short trains in a rather rural environment. But I prefer long international trains! So several years ago I started thinking about an outdoor circuit on the terrace. Of course, the big disadvantages would be the weather and the need to bring it in for the winter.

Would the tracks be able to withstand the exposure to humidity (because of course I was still planning on a tarp for when it was not in use)? Would the structure itself withstand the stresses, and for that matter, what materials should be used? That’s what I’d like to tell you here.

## First project: trial and error

For storage reasons, the circuit naturally had to be dismantled into several sections, which I will call modules. On the other hand, I wanted a looped circuit, to be able to run trains as long as necessary. Indeed, I had from the beginning the intention to make videos; it was therefore necessary to be able to make several takes without interfering in the running of the trains.

But there was no question of making an oval, which would take up too much space. I therefore chose the “dog bone” formula, which made it possible to follow two edges of the terrace without taking up too much of the middle. Of course, the extreme modules, which I call rackets, would necessarily take up more space. By the way, what would be the minimum allowable track radius? Since I was planning to use plywood panels, the maximum width was 1.20 m, which would lead to a radius of about 0.50 m.

Finally, the circuit would consist of five modules: from left to right, a racket A, a straight line module B, a module C of curves in the corner (planned parabolic curves), another straight line D, then the other racket E.

The first straight line module B should have several tracks to store some trains. A balloon loop was planned.

Here is the plan of this first project.

The length of the route is approximately 20 metres. The minimum bending radius of module C is 1100 mm.

The modules have 10 mm plywood sides. The visible side is 10 cm high and flush with the board; the opposite side is 15 cm high and protrudes beyond the surface to make a fall protection parapet. I forgot to mention that the circuit height is about 90 cm, and that material falling from this height onto the concrete slabs would look very bad.

The sides are fixed to the board by means of 20 mm cleats screwed into the corners. For the rackets, the visible side is curved. So I have to bend the plywood, and fix it with a cleat notched every 20 mm or so to follow the curve. The underside of the rackets is also reinforced with larger cleats. Unfortunately, the weight becomes quite important: I can hardly move them by myself.

### The interfaces

A big problem is the fixing of the modules together. Here again, I use cleats in the form of crosspieces connecting the sides. Precision is necessary, but not easy to obtain with wood that plays with humidity! I used stove type bolts that have an anti-rotation square under the head.

In this first project, single-leg supports for narrow modules, or two-leg supports otherwise, are sandwiched between the module crosspieces:

This assembly will prove complicated to implement and, above all, unstable. On the other hand, a well-made terrace has a slope for water drainage. This is the case here; so a means to adjust the height of the legs is necessary…

The connection of the tracks is done with sliding rail joiners that are retracted for dismantling and storage.

## Evolution of the project

The junction of the tracks in module B is not satisfactory: the trains twist in an inelegant way at the end of the curve in module C. In fact, this arrangement was intended to allow modules B and D to be combined in a straight line, without passing through the curve of module C. But, given the configuration of the site, this possibility was never used. So I’m moving the turnout area to module C, with curved turnouts, which will unfortunately force me to cheat on the track transition curves. But the tracks will be longer and the diversions more elegant.

An inspection trap door, mounted on a piano hinge, is cut out of module A. Module E is split into two parts, also mounted on hinges, which allows the smaller part to be folded down to facilitate circulation on this side, as this module is flush with the veranda, as can be seen in a photo.

### Some photos

View of module A.

You can see the embryo of the control panel, with toggle switches for the turnouts and push-buttons for the routes. For the programming of these routes, I refer you to the article Automation for train models.

View of module B.

View of module C.

Note the arches for market gardening tunnel which are used to support the protective tarp. In use, they are “planted” in the circuit board.

View of modules D and E.

### New supports for the modules

To replace the wobbly legs, I now use shelf supports on racks, fixed into the walls, and extended by cleats. One drawback is that they are made of steel which, although lacquered, will eventually rust, especially at the section of the racks I have cut out. I’ll give them a coat of rustproofing.

Detail of a rack support:

The tarp is now made of a sandwich of a survival blanket to prevent the greenhouse effect, and a polyethylene film for waterproofing, all joined by double-sided carpet adhesive tape. The last will age prematurely under the attack of UV rays: it is not made for this! I don't forget to leave openings for air circulation; this prevents condensation forming on damp mornings.

But frankly, it’s a pain to have to fold up the tarp every time I want to use the circuit, and to put it back on in the evening, unless I’m perfectly sure it won’t rain at night, which is quite rare…