Chisels used in metal work can be divided into two main categories: hot chisels and cold chisels.
Cold chisel A cold chisel is a tool made of
tempered steel used for cutting 'cold' metals, meaning that they are not used in conjunction with heating torches, forges, etc. Cold chisels are used to remove waste metal when a very smooth finish is not required or when the work cannot be done easily with other tools, such as a
hacksaw, file, bench shears or power tools. Cold chisels have a less-acute angle to the sharp portion of the blade than woodworking chisels. This gives the cutting edge greater strength at the expense of sharpness. Cold chisels come in a variety of sizes, from fine engraving tools that are tapped with very light hammers, to massive tools that are driven with
sledgehammers. Cold chisels are forged to shape and hardened and
tempered to a blue colour at the cutting edge. The head of the chisel is
chamfered to slow down the formation of the mushroom shape caused by hammering and is left soft to avoid brittle fracture splintering from hammer blows. There are four common types of cold chisels: • The
flat chisel, the most widely known type, is used to cut bars and rods to reduce surfaces and to cut sheet metal that is too thick or difficult to cut with
tin snips. • The
cross cut chisel is used to cut grooves and slots. The blade narrows behind the cutting edge to provide clearance. • The
round nose chisel is used to cut semi-circular grooves for oil ways in bearings. • The
diamond point chisel is to clean out corners or difficult places. It is also useful for "pulling over" centre punch marks wrongly placed for drilling. Although the vast majority of cold chisels are made of steel, a few are manufactured from
beryllium copper, for use in special situations where non-
sparking tools are required. Cold chisels are predominantly used in
Repoussé and chasing processes for the fabrication of
bronze and
aluminium sculptures.
Hot chisel A hot chisel is used to cut metal that has been heated in a
forge to soften the metal. One type of hot chisel is the
hotcut hardy, which is used in an
anvil hardy hole with the cutting edge facing up. The hot workpiece to be cut is placed over the chisel and struck with a hammer. The hammer drives the workpiece into the chisel, which allows it to be snapped off with a pair of
tongs. This tool is also often used in combination with a "top fuller" type of hotcut, when the piece being cut is particularly large. ==Stone==