I recently got a metal lathe. The first project I planed was a oscillating engine. Since I have not worked much on a lathe before I decided to make a wooden prototype to get to know the machine. Also, if I messed up, I would only waste a few pieces of scrap wood. Luckily for me I have lots of scrap wood since a dead tree fell over in our garden. I am quite impressed how easy it was to use the lathe (on wood) and the engine works quite well.
The engine runs on a small air pump that I have in the shop (or on lung power). The next engine will be the real deal made from metal and run on steam. I plan to build a small brass boiler to generate the steam in. The whole mechanism will be mounted on one of my models to make it run via steam power. Stay tuned to see the progress of this idea.