A small air engine I machined from scraps of metal for a class, using measurements and tolerances provided by the professor, and a variety of lathes, milling machines, and other smaller tools

There is really no practical use for it, but if you hook an air compressor hose up to the brass inlet about three-fourths up the device, it does at least run like an engine.

Built by myself as part of a physics project competition (which my group won), after my group made a smaller model to test the design

Though it cannot launch a 90kg projectile over 300 meters, it can easily launch a softball over 70 meters

Hewed from a hickory log

Carved with a draw knife