Tunnels Are Boring

Posted on June 17th, 2017, by Michael Rountree

Where my main line enters a helix between Oxmore and Trellisville, I needed to dress up the entry and exit as tunnel portals. In the past I’ve just used a portal casting and nothing else, but it doesn’t look realistic to not see the walls of the bored out tunnel behind the portal. I decided to fabricate some liners for the first few inches of track, and this is how I did it.

My primary building material is a sheet of polystyrene, which came in the form of a “For Sale” sign bought at the hardware store. This is cheap, but the drawback is that it has printing on one side, and that ink must be sanded off anywhere you need to make a glue joint.

Sheets and sprues

In addition, I used old sprue material for reinforcing, as well as some Lego blocks. I use Legos as a way to build subassemblies that snap together. The plastic that Legos are made of will soften with glue meant for styrene, you just have to pre-apply glue to soften it first, then apply glue again when ready to make the joint.

Braced arches

I just used nippers to cut the sprues and didn’t bother cleaning things up much, except that I had to make minor corrections in order to leave room to add a few blocks of square styrene for a better joint; you’ll see those later. I cut these arches to be full height, but you’ll see later that the side walls are cut 1/2″ less each side.

Laying out the walls and arch roof

For the main walls and the arched roof, I cut out most of the arch past the first few inches. This will allow the tunnel walls to flex in order to follow the curvature of the track. The big sheet here is going to become side wall, arch, and side wall… but then there are two 1/2″ strips above it that will become the very bottom of the side walls.

Assembly in a Lego cradle

I built a little jig of Legos to hold the side walls while gluing things up. The sheet has a lot of springiness to it and will resist taking the arch shape. In a previous version (for the other portal), I didn’t use sprues for bracing the arch, and it proved inadequate to hold the shape. The walls bowed outward and bent the arch into crazy shapes!

Squeezing the Lego cradle

The cradle makes gluing much easier. I had drawn a centerline on both the arches and the roof sheet, so I just aligned that line, and then used the Lego cradle as a way to squeeze the sheet into the arch form. On the lower portal with the red ink showing, you can see the square rod that I added in places in order to get a lot of glue surface area. Just glue everything up and hold it tightly until the glue cures.

Now it’s time for those 1/2″ strips, which will become the base of the liner. I used a Lego block to make a nice perpendicular joint to a footing pad. I made a pad for each end; the one at the front is longer since it will mate up with Legos at each of the stiffening arches. But there’s no magic to the sizes of these, I just used scraps from cutting the sheet.

Another Lego footing pad

The far / deep end of the liner just has one Lego connection and a smaller footing pad. The blue Legos are glue to the upper wall, and the green Lego is glued to the lower wall.

Finished front footing

After the first Lego is firmly glued in, you can position the wall over it in order to locate the second one, which wants to fit up tight to the second arch. The way the arch extends down is a way to align the parts, though maybe it isn’t truly necessary since the Legos hold things so well.

Footings in place

So why bother making separate footings? This arrangement lets me have access inside the tunnel, to ballast the track, with the ballast going right up to the wall. Plus, it makes it a bit easier to align the curves of the wall to match the track.

Inserting the roof

With the footings glued down firmly (I used a 2-part epoxy), all I have to do is snap the roof in place. The height of the deep walls was cut to be just below the plywood of the helix subroadbed, so there wasn’t going to be room for an arched roof there anyways, but the ability to curve the walls is great, too.

Finished portal assembly

And here is how it all looks once assembled. The portal casting is just loose in this shot, but you can see that I made my arches to match the size of the portal’s arch. The slight light leak at the joint between upper and lower walls will hopefully disappear once this is all dark and under a mountain, but I might just use some tape on the back side to be sure. This portal is the first iteration and you can see how the rear arch (in red and black) is all warped. The Legos hold it in shape, though, and in this case I added an additional Lego buttress (the grey block in the middle). I also learned from this that you don’t want to spray paint without masking off the Lego nubs, because they are engineered to such tight tolerance that even a bit of paint can make it hard to snap back on!

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