Cut an eight-foot board into one-foot pieces and you only get seven
Try slicing an eight-foot plank into one-foot lengths with a saw that removes an eighth of an inch per cut. You end up with seven good pieces and an eighth that falls short by seven-eighths of an inch. The culprit is the kerf, the slot of wood every blade turns into sawdust.
Kerf width depends on more than blade thickness. Most saw teeth are bent slightly outward, alternately left and right, a feature called set, so the cut is wider than the blade and it does not jam. Wobble widens it further, which is why an overly thin blade can paradoxically waste more wood. Flush-cutting saws keep one face perfectly flat, with teeth bent only the other way, so they can trim a dowel level with a tabletop without marring it. Tooth spacing has its own quirk: counting points per inch always gives one more than teeth per inch, because both ends of the inch are counted.
The first saws were naturally jagged things: flint, obsidian, shells and shark teeth. Serrated tools with traces of woodcutting from Pech-de-l'Aze cave in France date to between 90,000 and 30,000 BCE. Egyptians were using copper pull saws by the Early Dynastic Period, and a tomb from King Djer's reign in the 31st century BC held many of them; tomb paintings show carpenters at work. Iron Age smiths learned to stretch thin blades taut in frames, and the earliest known sawmill, at Roman Hierapolis in the third century AD, cut stone.
Chinese legend credits the saw to Lu Ban, while Ovid gave the honour to Talos, the nephew of Daedalus. Much later, Sheffield's crucible steel, hard and springy with a fine polish, made the English city the world's saw capital; by the 1820s it housed over half of Britain's saw makers, until American mechanisation and tariffs overtook it.
Before water-powered mills spread in colonial North America, planks came from pit saws worked by a man in a pit beneath the log and another standing above. Those sawyers were among the best-paid labourers of the era. Today most handsaws are cut by laser, with flame-hardened teeth that stay sharp until the saw is simply replaced.
Source: Saw
