A Timeless History
Water was lifting hammers long before Leonardo. Around AD 20 the Chinese scholar Huan Tan wrote of pounding hammers driven by water. Pliny, in AD 77, knew Italian pestles worked by "wheels which water turns". From the Middle Ages, cams on a water wheel's axle drove forge hammers, ore stamps and fulling mills across Europe. Leonardo's file-cutter of about 1480 is one of his first complete machine drawings.
SourceMuseo Galileo, leonardo//thek@, Codex Atlanticus f. 24 r (ex 6 r-b), c. 1480 — teche.museogalileo.it · Pliny, Natural History XVIII.97 — LacusCurtius, University of Chicago · Needham, Science and Civilisation in China IV:2 (Cambridge, 1965) · Science Museum Group, object 1952-451
Science In Action
A cam is a bump on a turning shaft; the part it pushes is the follower — here, the tail of the hammer • Rotation in, lift out: as the cam comes round it raises the follower, then drops it as it passes • The fall is gravity's job — the shaft only lifts, so the blow lands the moment the cam lets go • More cams, more blows per turn: Agricola in 1556 put two cams on the shaft for every stamp
SourceEncyclopaedia Britannica, "cam" — britannica.com · Agricola, De re metallica (Basel, 1556), Book VIII, Hoover trans. 1912 · Museo Galileo, leonardo//thek@ (Landrus 2013 entry)
Arts
Leonardo drew his hammer as he drew all his machines: in perspective, every peg and lever visible, the note written left to right, the way anyone can read it. The water-driven hammer became a subject for painters too. In Joseph Wright of Derby's An Iron Forge (1772) a tilt hammer, its great wooden helve lit by the white-hot bar beneath it, works at the centre of the picture while the smith's family looks on.
SourceTate, T06670 — tate.org.uk · Museo Galileo, leonardo//thek@, ATL.0047.1 (Landrus 2013)
Applications Today
The cam never went away. In every petrol and diesel engine a camshaft turns with the crankshaft, carrying one cam for each valve; as each lobe comes round it pushes its valve open for a precisely timed instant and a spring snaps it shut — over a thousand times a minute. Cams also drive sewing machines, printing presses and automatic machine tools. The lift-and-release of Leonardo's hammer is the engine's heartbeat.
SourceEncyclopaedia Britannica, "cam" — britannica.com · Library of Congress, FSA/OWI Collection, LC-USE6-D-005039
One more thingAround AD 20 Huan Tan wrote that treading a tilt-hammer made pounding ten times more efficient — and that water power made it a hundred times.
SourceHuan Tan, Xinlun, c. AD 20, quoted in Needham, Science and Civilisation in China IV:2 (Cambridge, 1965)
A water-driven hammer from Holbeam Mill, Devon, forged sickles until 1942; it is now in the Science Museum.
Shui dui tu — a battery of trip hammers on an axle turned by a vertical water wheel (grain-hulling), woodcut illustration — Song Yingxing (Chinese, 1587–1666), Tiangong Kaiwu — 1637 (photograph of the illustration as reproduced in E-tu Zen Sun & Shiou-Chuan Sun's translation, Pennsylvania State University Press, 1966, p. 93) — Wikimedia Commons 'File:Hydraulic-Powdered Trip Hammers.jpg' (933 × 756; the 1280-px Commons rendering used, converted to greyscale, levels, cropped to 4:3, upscaled to 1400 × 1050) — Tiangong Kaiwu, ch. 4 (Cui jing)
