first step was to design the 3D printed underframe and figure out how to build the top half from sheet brass. The second step was adding all those rivets before a quick third post with the metal top posed on a 3 bar slab wagon to give a rough idea of the final model. The final piece of the puzzle was actually printing the underframe.
This is the first model I've designed in which I've combined a 3D printed part with parts from another material and I'm really happy with how it's turned out. I could have tried to 3D print the whole model but the upper body would have been way too chunky; I used 0.12mm brass but the thinnest I could have printed the parts would have been 0.3mm and I'd probably have had to have the side walls at 0.6mm as they would have been unsupported during printing.
The use of two materials did leave me wondering if it was worth making the model available to others or not though; painting a 3D printed model is much easier than fabricating half the model from a flat sheet of brass. In the end I've decided that the top is easy enough to make (see my nice detailed instructions) that most people should be able to make up the part without any issues. I've made up quite a few of them now to check the instructions and to find the best order of the folds etc. that I'm fairly certain that anyone with a sharp pair of scissors a modelling knife and something to help make the folds could make the part almost without thinking. So if you fancy a go (just to prove me wrong) then I'll happily sell you an underframe or three.