During December 2005, I was working on a model railway. It's something that happens to me occasionally - I make so much terrain that I decide I should make a model railway. I never finish them.
This time, something different happened. Sure, I never finished it. But I ended up with a 40K railway instead.
As a joke, my brother gave me a $15 toy train set he got from Toys'r'us. It's 'O' gauge, which looks right for 40K. He never though of it that way. I though of it that way right from the start.

The first thing to do was to 40K-ify the engine. There was plenty of detail on it to start with, so I didn't want to cover any of it. The wheels looked a bit toy-like (especially the ones with rubber tyres for extra grip). I figured big side skirts looked very 40K, so that fixed that.

The engine came with piston assemblies, and fake drive rods. Since all of that would be hidden behind the skirts, I removed it. I refitted the pistons after modification. Big smoke deflector plates where attached at the front. Somehow, they make the steam engine look futuristic. I also used a big imperial guard bulldozer blade, reshaped into a 'V' for the cow catcher look.

The biggest change was converting the engine from a Tender engine (i.e.: one which tows around a coal wagon) to a Tank engine (one which carries fuel in tanks down the sides of the boiler). The engine already had tanks in place, but the set included a tender. I didn't like that look to much, plus the engine had a different kind of couple on it. So I chopped off the last 2 cm of the tender, and grafted them to the back of the cab.

With some judicious and cunning plastic work, I was able to incorporate the right kind of coupler mechanism, and still allow the battery cover to be removed. This allowed me to retain the electric motor, sound and light so the engine could still run.

A few Imperial Icons, an a coat of green paint rounded out the engine. I also added identification numbers using Letracet. Time to start on the rolling stock.