Power hammer. By Joe the Builder. 10:48 video:
https://www.youtube.com/watch?v=DNixCN2HF5M
Previously:
https://www.homemadetools.net/forum/...369#post154516
https://www.homemadetools.net/forum/...058#post137994
https://www.homemadetools.net/forum/...100#post115522
https://www.homemadetools.net/forum/...6821#post84414
https://www.homemadetools.net/forum/...1314#post74161