Ball-peen hammer
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A ball-peen or machinist's hammer,<ref>Template:Cite book</ref> is a type of peening hammer used in metalworking. It has two heads, one flat and the other, called the peen, rounded. It is distinguished from a cross-peen hammer, diagonal-peen hammer, point-peen hammer, or chisel-peen hammer by having a hemispherical peen.
Etymology
In the word "ball-peen", peen,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}.</ref><ref name="iforgeiron">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="technologystudent">{{#invoke:citation/CS1|citation |CitationClass=web }}.</ref> probably comes from a North Germanic source; compare dialectal Norwegian Template:Lang ("peen"), Danish Template:Lang ("peg"), German Template:Lang ("the peen of a hammer"), Old Swedish Template:Lang ("to pound iron with a hammer").<ref>"Peen" in wikdictionary.</ref>
Uses
Besides peening (surface-hardening by impact), the ball-peen hammer is useful for many tasks, such as striking punches and chisels (usually performed with the flat face of the hammer). The peening face or ball face is useful for rounding off edges of metal pins and fasteners, such as rivets. It can also be used to make gaskets for mating surfaces: a suitable gasket material is held over the surface that needs a gasket, and the operator lightly taps around the edges of the mating surface to perforate the gasket material.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}.</ref>
Crime
The ball peen hammer has been described as “the favourite weapon” of the Hells Angels.Template:Sfn It was also the weapon used by Peter Sutcliffe, dubbed the Yorkshire Ripper, an allusion to the Victorian serial killer Jack the Ripper, to murder at least 13 women and attack a further possible nine.
Variants
Variants include the straight-peen, diagonal-peen, and cross-peen hammer. Instead of a ball-shaped head, these hammers have a wedge-shaped head. The straight-peen hammer has a wedge oriented parallel to the hammer's handle. The cross-peen hammer's wedge is oriented perpendicular to the handle.<ref name="technologystudent"/> The head of a diagonal-peen hammer, as the name implies, has a wedge set at a 45° angle from the handle; it can be a left angle or a right angle, and some peen hammers have a double diagonal wedge<ref name="iforgeiron"/> for ergonomic reasons.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}. See also "Forging the double diagonal peen hammer part 2".</ref> They are commonly used by blacksmiths during the forging process to deliver blows for forging or to strike other forging tools.
Head materials
Ball-peen hammer heads are typically made of heat treated forged high-carbon steel<ref>Template:Citation.</ref> or alloy steel; it is harder than the face of a claw hammer.Template:Sfn Softer brass heads are sometimes used.