Chapter 7 - Sawing, Chisels and Files

Abstract

A saw consists of a series of narrow single cutting edges (teeth), arranged either along a straight edge (reciprocating hand saw or continuous band saw) or around the circumference of a disc (circular saw). Specialist saws include hole (trepanning) saws where the teeth are arranged around the end of a tube; the corresponding “hole knife” is the cork borer, apple corer, or hollow cheese sampler. The cutting edges of saw teeth are perpendicular or oblique to the direction of motion of the saw and this distinguishes saws from knives. In plan view, saw teeth are bent (set) sideways alternately to right and left, and therefore cut a path slightly wider than the thickness of the blade. This reduces contact between blade and workpiece, hence reducing friction, heat generation, possible overheating, and damage of the blade. A chisel is a type of knife but unlike a hand-held knife where “sawing” often occurs, the principal motion is perpendicular to the cutting edge. Bolsters are chisels splayed out at the edge for cutting bricks. Different materials respond differently to chisels: a large piece of timber can be split down the grain by a blow from a chisel but it is impossible to split a block of metal by hand with a cold chisel owing to the much higher toughness of metals and the fact that the deformation is in the ductile range.