Some chisels are made of beryllium copper so they will never spark
Almost every cold chisel for cutting metal is hardened steel. But where a single spark could be disastrous, toolmakers use beryllium copper instead. It is one of many small adaptations that turn a simple wedge on a handle into dozens of specialised tools for wood, metal, stone and leather.
A chisel is a wedge-shaped edge driven into material by hand pressure, a mallet, a hammer or, in industry, a hydraulic ram or trip hammer. Woodcarvers typically start with large tools and work down to small ones for detail. At the big end sits the slick, used in timber framing and wooden shipbuilding. Mortise chisels have thick, rigid blades for cutting joints, and woodturners' tools get extra-long handles to resist the downward pull of wood spinning on a lathe.
Metalworking chisels come in hot and cold versions. A cold chisel cuts unheated metal and is ground to a blunter angle than a wood chisel, trading sharpness for strength. It is forged, then hardened and tempered until the edge turns blue, while the striking end is chamfered and left soft so it will not shatter under hammer blows but slowly mushrooms instead. Variants include the round nose, which cuts oil grooves in bearings, and the diamond point, which can nudge a misplaced centre-punch mark. Blacksmiths use a hot chisel called a hardy, set edge-up in the anvil, so the hammer drives glowing metal down onto the blade.
Stoneworkers cut bricks with a bolster, tapping a groove along the line and then striking the centre hard to crack it. Sculptors favour a bent spoon chisel bevelled on both sides. Masonry chisels for demolition are deliberately dull so they wedge and break rather than slice, and leatherworkers use a pronged chisel that punches a row of stitching holes at once.
Gouges, chisels with curved blades, are graded by a sweep number that describes how much of a circle the edge covers, from No. 1, nearly flat, to No. 9, a semicircle, with a U-shaped No. 11 and V-shaped parting tools numbered higher still.
Source: Chisel
