Tanktainers In N Scale

I’ve always been fascinated by the seemingly endless design variety and livery variation of tank containers.

VOTG 2CT6 by Col André Kritzinger – Own work, CC BY-SA 3.0, from Wikimedia Commons, View Image

So I decided it was finally time to have a go at creating some CAD models and produce my first 3D prints…

The process started by finding some good reference photographs and picking a container to model. I managed to get some time on the Internet while house-sitting and found a number of websites with good reference shots. The best reference for my first attempt was the website of a company called Meeburg ISO Tanks & Containers. Meeburg sell refurbished and second-hand containers and their website includes pictures of most of the containers they sell from nearly every angle. Very useful.

I eventually decided upon an 8 x 8 ISO tanktainer with a fairly simple frame.

Next I had to scale these images down to N scale; luckily that isn’t too difficult as ISO containers are fixed widths. The height and length can vary but it’s usually possible to determine these dimensions using the type code and other markings on the side of the container. These known dimensions can act as a scale to help determine other unknown dimensions in the photographs in a similar way to the method described in this post.

The only problem that I ran into while scaling images is that even a fairly face-on photograph of a large object such as a container is likely to have some perspective distortion. The part of the object furthest from the camera is likely to appear smaller and this can really play havoc with your calculations if you’re not looking out for it. If I don’t have a definite measurement I tend to make an educated guess based on other known measurements and in some circumstances it’s possible to use the average between two conflicting measurements.

Once I had scaled the major measurements, I was able to start creating my CAD drawing. I use a program called FreeCAD. It looks complicated but it’s fairly straight forward once you’ve spent a little time playing with it.

With FreeCAD you use a series of 2D drawings called sketches to create a 3D object. Although 3D printing allows us to create complex objects as a single piece rather than as a series of separate pieces (required by most manufacturing techniques) when using FreeCAD it’s helpful to think about the item you are creating as a block of wood or metal. Your first 2D sketch creates the rough outline of your block (height and width). This is then turned into a 3D object by adding length/depth (a process known as padding). Subsequent sketches can then be attached to any face of this initial shape and can change it by adding new material or removing unwanted material. It’s a hard concept to describe but there are lots of helpful tutorials that explain the steps and once you see it in action it’s fairly self explanatory.

I ended up producing the model in two parts: the frame and two ends as one model and the tank itself as another model.

Frame and ends joined by sprues.

Tank with ends joined by sprues.

3D printers can’t use CAD files directly. So I used FreeCAD to produce a mesh file (.stl) that 3D printers can use and uploaded it to 3D printing service Shapeways.

I was very pleased with the overall result of this first attempt. The model I received back from Shapeways is very detailed and the material is actually quite flexible (I was worried it would be very fragile) and the frame and tank went together as planned. Unfortunately, something did go wrong and I found that the tank I received was solid rather than hollow. An expensive mistake that I made while creating the mesh file. I somehow didn’t notice when uploading the model to 3D printing service Shapeways.

Of course there are a couple of changes that I can make to produce an even better model. I’ll talk about these in another post, when I’ve got a camera to get some pictures but all in all it was a very satisfying project and I’m already working on more. I also need to look at producing some decals and also etches for very fine details that won’t print well such as ladders and walkways.

Watch this space…

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