Stirling engines provide a way to turn heat into linear, then rotary motion. They were invented around the time of the steam engine, but never took off to the same degree; nowadays they’re making a comeback as a way of turning heat from the sun into something more harvestable. This example, with its incredibly small 0.02cc engine, won’t be powering a sustainable future for us, but it does give us a brilliant insight into just how accurately a skilled machinist can make things out of metal. You really have to watch the video to get a sense of the scale of the engine. We watched fairly unimpressed for a few minutes until a giant pencil hove into view, suddenly giving us a sense of scale and wonder. For example, the pins that connect the beam of the engine to the piston is made from 0.8 mm piano wire. That’s impressive, but even more impressive is the fact that one of those pins had to be cross-drilled and fitted with an even smaller 0.4 mm pin.