I hope it works out to be interesting!

I've recently converted a small motorcycle to electric power and would like to have a go at making a streamlined electric trike next year. One way to make the body would be to machine slices of thick extruded polystyrene into rings, then glue the rings together to make the body. The foam can then be covered in epoxy/glass (or maybe kevlar) composite, to produce a complex 3D foam sandwich monocoque. The idea is to use the body shell as the chassis, with bonded in hardpoints for suspension mounts etc.

A CNC router would be an ideal way to accurately make these mould slices, as (with luck) I should be able to just take the slice layouts from Rhino and pass them to Mach 3 to drive the machine. My plan is to build something with a working volume of around 750mm x 600mm x 300mm, with a fair degree of accuracy but without any need to be able to cut heavy materials.

I've already tried hand-held hot wire cutting foam, but it's challenging to get a fair enough shape; the hand-held hot wire leaves a lot of small ripples that need to be sanded out, even when used with guide templates.

Having made a few foam composite parts now (by hand) I'm impressed with the technique. I can see why Burt Rutan (of Scaled Composites fame) developed this technique for his home-built aircraft projects, as it's well within the bounds of a normal DIY skills, yet produces light, stiff and remarkably strong structures.

Jeremy