Tinkerer extrordonaire Kurt Bjorn built this miniature 9-cylinder radial engine from plans in his home machine shop. He thought of an improved cylinder head design that he wanted to try out, so he built a foundry furnace and taught himself metal casting in order to fabricate the heads.
Kurt has also built a miniature turbine engine complete with homebuilt ECU. He publishes serialized accounts of these and numerous other equally amazing acts of model engineering under the 5 Bears Research moniker.
I have been watching Kurt’s site for a few years and have been inspired to construct my own foundry furnace.