SP Concrete Telephone Booths

Here's the result of that laser light show - a lot of Southern Pacific concrete telephone booths. These were placed out at the ends of sidings out in the boonies, and gave the crews a way to contact the dispatcher in the days before radio.

These are great models for 3d printing - they're small, geometrically simple, annoying to scratch build, and rare enough so they're unlikely to be at the hobby shop. (To be fair, there are two manufacturers making the more modern versions of these, so I'm exaggerating a bit... but you get the idea - little, railroad specific details like this are perfect for 3d printing.) I'm not even the first one printing these; someone's selling 3d-printed N scale models on the Shapeways site. Building the 3d model in SketchUp took probably an hour and a half, and I was looking at finished models later that evening. There are even plans and drawings available in the Common Standard Plans books.

3d printing really comes into its own when you need a bunch of these. As the video showed, printing twelve of these wasn't a stretch. The first run had one obvious problem - SketchUp, because it's intended for architectural models, draws curves surfaces as a set of flat facets. By default, it uses 24 faces for a cylinder, or six faces for a 90 degree turn. On the first models, I could see the pattern on the model. Redoing the model with 48 faces/cylinder appears to make surface look perfectly curved. (Hint: when drawing a circle, type "48s" in the text box at the bottom of the window to change a circle to 48 sides.) Even with that problem, the models came out awfully nice, with the doors crisp, and some added coarse detail for hinges, latch, and handle all being visible under the magnifying glass. The models did get the characteristic vent holes in the door, though it's hard to see on the model. Although the upper panel in the door looks solid, it's glass in the real model. Rather than create an opening, I'm planning to paint the panel gloss black to look like glass.

And so now I've got something like 24 telephone booths, when I need maybe four on my layout.

I printed these telephone booths upside down. Because I print the model hollow, printing it from the bottom up would have trapped resin in the body; printing upside down gives the resin a chance to escape. The photo shows the support structure added by the 3d printer to handle the uneven surface; I cut off the support with diagonal cutters and finish with an x-acto knife and file.

Even though I've got twenty-four phone booths, they're not quite right. The second version got rid of the stair-step pattern and made the door more obvious, having it stick out two inches instead of one for better definition. Looking at real photos also shows some problems. This photo, for example, shows strap hinges. It's also obvious that the door's set back into the concrete cylinder. That little detail would be worth adding, but doing so would add the challenge of trying to highlight the separation between the door and the frame. That's the sort of decision that folks worry about in mass-production: what do you need to do to make the detail stand out, or make it easy to paint the model, or make it easy to build? (Think of the exaggerated detail of hood doors on diesel locomotives.) While setting the door and frame into the cylinder is realistic, I'd need to add a line between door and frame that'll need to be out of scale.

I also have to figure out how to finish them appropriately. I'm suspecting I'll be giving these out as party favors for a while, so figuring out to mass-paint a bunch of these would be a big win. I'm out of my normal concrete-gray spray can, so I'll show some painted models after my next trip to the hobby shop. I'm also starting to run out of my favorite Polly-S colors now that Testors stopped making the railroad colors, so I suspect I'll be in the market for new railroad paints soon.

Coming soon: the 3d flat cars are still going; I've tweaked the designs a couple times to match photos, and I've painted and decaled one. Because I had very few spare sets of decals with 1930's weights and dimensions, that decaling was painfully fiddly. Because I know I'm going to print at least 6 or 7 flatcars, I'm hoping to custom-print decals to make the job go faster. More news later...